•A novel red phosphor Li2MgTi3O8:Mn4+ was prepared by the soft chemical method.•Li2MgTi3O8:Mn4+ gives a deep red emission with a good QE and thermal resistance.•Li2MgTi3O8:Mn4+ can act as a novel potential red phosphor for warm white LEDs.We describe the preparation of a novel red-emitting Li2MgTi3O8:Mn4+ nanocrystalline phosphor by a soft chemical method. Li2MgTi3O8:Mn4+ phosphor gained our attention and interest due to its low-cost and unique luminescent properties. The deep red emission from Li2MgTi3O8:Mn4+ shows an abnormal broad band at 680 nm, with a quantum efficiency (QE) of 34%, and good thermal resistance of ΔE = 0.214 eV Li2MgTi3O8:Mn4+ phosphor exhibits the most intense excitation absorption in the blue region which matches the emission wavelength of the blue LEDs, indicating its potential to enhance the color rendering performance of white LEDs. The deep red emission originates from the 2Eg → 4A2g transition of Mn4+. The spectral features are well explained by the Tanabe-Sugano diagram, with crystal-field and Racah parameters of Dq = 2.06 × 103 cm−1, B = 0.76 × 103 cm−1 and C = 3.00 × 103 cm−1. A device was fabricated in which this red phosphor Li2MgTi3O8:Mn4+ was used to coat the blue LEDs. The fabricated device demonstrated that the prepared material can act as a novel potential red phosphor for warm white LEDs.

A single-phase white-light emitting phosphor LuNbO4:Dy3+ was synthesized using the solid state method in air for the first time. X-ray diffraction (XRD) along with excitation spectra, emission spectra, decay times and thermal stability were exploited to characterize the asprepared phosphors. Under ultraviolet (UV) excitation (261 nm), the self-activated emission of the LuNbO4 host is peaked at 402 nm with a broad emission band ranging from 320 nm to 600 nm, ascribing to the charge transfer in NbO43− groups, which has spectral overlapping to the excitation of f–f transitions of Dy3+ in LuNbO4:Dy3+ phosphors. They show both the broad host emission and sharp emission lines due to the characteristic f–f transitions of Dy3+ ions, which exhibit tunable white light emissions due to the energy transfer from the NbO43− groups in the host to Dy3+ with increased Dy3+ content. The optimal chromaticity coordinates and Correlated Color Temperature (CCT) in LuNbO4:Dy3+ are (x=0.336, y=0.311) and 5299 K, respectively, which occur when the doping Dy3+ is 0.01. The decrease of decay lifetime for host emission in LuNbO4:Dy3+ with raised Dy3+ content demonstrates the energy transfer from the host to Dy3+. The energy transfer mechanism in LuNbO4:Dy3+ phosphors was determined to be a resonant type via dipole–dipole mechanism. Moreover, good thermal stability was also identified in Lu0.99NbO4:0.01Dy3+ and its emission intensity was reduce to 85% of its initial value at 100 °C and 62% at 200 °C, the chromaticity color coordinate values of Lu0.99NbO4:0.01Dy3+ had a slight shift with raised temperature. The current research suggests that LuNbO4:Dy3+ could potentially serve as a single-phase white-light emitting phosphor in solid-state lighting and display fields.

Novel green emitting long lasting phosphorescence (LLP) Li1.14Zn1.43SiO4:Mn2+ (LZS: Mn2+) was prepared successfully through a conventional solid-state reaction. Phase purity was checked by X-ray diffraction. The photoluminescence and afterglow properties of as-prepared phosphors were studied systematically by diffuse reflectance spectra, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence glow curves measurements. The photoluminescence spectra and LLP spectra indicated that LZS: Mn2+ phosphors exhibits green emission center at 526 nm originated from 4T1→6A1 transition of Mn2+. The duration of Mn2+ doped Li1.14Zn1.43SiO4 phosphors can last about 1 h. Thermoluminescence glow curves indicated that the LLP of LZS: Mn2+ phosphor was generated by the suitable trap depth. Based on the experimental results, a model was constructed to discuss the mechanism of afterglow briefly.

Red-emitting long-persistent phosphor Mg2GeO4: Mn4+ was prepared by a high-temperature solid-state reaction. The photoluminescence and afterglow properties of Mg2GeO4: xMn4+ phosphors were studied systematically. Furthermore, to improve the afterglow performance, co-doped Re3+ (Re = Pr, Er, Nd and Yb) ions into Mg2GeO4: 0.001Mn4+ separately to adjust the trap depth or increase the trap density was performed. The duration of Mg2GeO4: 0.001Mn4+ can be observed 30 min by naked eyes, and the initial brightness and afterglow duration are significantly improved after Re3+ ions are doped respectively. Especially, the afterglow emission of Mg2GeO4: Mn4+, Yb3+ can last for 2 h. This investigation shows up a rare Mn4+-doped long-afterglow phenomenon, and provides a new and efficient red afterglow material for potential application.

Focusing on the improvement of persistent duration, we used photoluminescence and thermally stimulated luminescence measurements to study the influence of different codopants M3+ (M3+ = Tm3+, Ga3+, Pr3+, Yb3+, Nd3+) on the luminescent quantum efficiency and traps distribution of Cr3+-doped stannate-baded long persistent phosphors (Zn2SnO4:Cr3+). This work reveals that Tm3+ is the most suitable codopant for enhancing the luminescent intensity and providing optimal trap depth for room temperature afterglow. This afterglow dependency toward the luminescent quantum efficiency of activator and traps distribution in host give us an important enlightenment, that is, when setting up a strategy of designing a long persistent phosphor, it is must integrally investigate the influence of these two factors.

Novel Eu2+ and Mn2+ doped fluorapatite-type Sr3YLi(PO4)3F powder materials have been synthesized via high temperature solid state reaction. The samples are characterized by X-ray diffraction (XRD), scanning electric microscopy (SEM), photoluminescence (PL) and photoluminescence excitation (PLE) spectra. Eu2+ single doped Sr3YLi(PO4)3F host displays a blue emission ranging from 400 to 550 nm centered at 439 nm, and exhibits a broad excitation band varying from 225 to 425 nm which matches with commercial n-UV LEDs (360–410 nm). Under near-UV light irradiation in the range from 270 to 410 nm, Eu2+ and Mn2+ co-doped Sr3YLi(PO4)3F phosphors show two emission bands centered at 439 and 565 nm, respectively. The relative intensity ratio of Eu2+ and Mn2+ can be changed by increasing the amount of Mn2+ ions, the emission color can be regulated from blue to white. The energy transfer process from Eu2+ to Mn2+ has been proved to the resonant type through the quadrupole–quadrupole interaction mechanism. It is important that the white light emission can be gained by modulating the relative contents of Eu2+ and Mn2+ ions in Sr3YLi(PO4)3F host. Base on the obtained results, the as-prepared phosphors might be applied as a candidate for white LEDs.

Herein, novel photochromic materials, Sr3YLi(PO4)3F:Eu2+,Ln3+, have been prepared by a conventional high-temperature solid-state reaction. Eu2+ singly doped Sr3YLi(PO4)3F showed reversible colorless-magenta photochromism when alternately irradiated by UV and visible light (or thermal treatment). Thus, Sr3YLi(PO4)3F:Eu2+ might be a potential candidate in various fields such as in imaging, sensors, photo-switches, and erasable optical storage media. The optimal Eu2+ doping concentration is experimentally determined to be about 0.5 mol%. The coloring and bleaching processes are attributed to electron trapping accompanied by the generation of F-centers and detrapping by different traps, respectively. Thus, these processes open a window for us to design a simple way to regulate and control the photochromic performance just by adjusting the doping concentration of Eu2+ ions or co-doping Ln3+ ions. On the basis of thermoluminescence, a schematic of a photochromic mechanism has also been proposed.

A novel Na3Y(VO4)2:Eu3+ phosphor was synthesized by the conventional solid-state reaction method. The phase formation and particle morphology were characterized through X-ray diffraction and scanning electron microscope, respectively. Photoluminescence (PL) characteristics such as excitation, emission, diffused reflectance spectra and decay curves, as well as temperature dependence of the PL spectra were investigated. Under the excitation of near ultraviolet (near-UV, 395 nm) and blue (466 nm) light, the Na3Y(VO4)2:Eu3+ phosphor can emit intense red emission, and the optimal doping concentration of Eu3+ ions is about 50 mol %. The major concentration quenching mechanism is determined to be the dipole–dipole interaction. The emission intensity of Na3Y0.5(VO4)2:0.5Eu3+ phosphor is much superior to the commercial Y2O3:Eu3+ under the near-UV excitation, and the luminescence intensity at 200 °C remains 74 % of T = 25 °C. The obtained results suggest that Na3Y(VO4)2:Eu3+ might serve as a promising red phosphor in white-light emitting diodes and display application.

In this work, we report a bifunctional phosphor Sr3Sn2O7:Eu3+ which shows red luminescence and photochromism properties. All as-prepared Sr3Sn2O7:Eu3+ samples were studied systematically by X-ray diffraction, photoluminescence spectra, diffuse reflection spectra, thermoluminescence glow curves. The optimum doping concentration of Eu3+ for the PL emission was determined to be 0.2. Concentration quenching and thermal quenching in photoluminescence (PL) emission were discussed in detail. Meanwhile, the material can change its surface color from white to brown under ultraviolet (UV) (254 nm) irradiation. The colored sample is bleached by blue light (400 nm) irradiation or heat treatment. The coloration-bleaching process is reversible, which makes it potential to be used in the field of photo switchers, erasable optional memory medial and sensors. Finally, a model is proposed on the basis of experimental results to discuss the mechanism of photoluminescence and photochromism in Sr3Sn2O7:Eu3+ in detail.

•Tb3+ doped Y3Al2Ga3O12 phosphor presents a white long persistent luminescence.•Trap depths, distribution and types was studied deeply.•The persistent luminescence mechanism of Y3Al2Ga3O12:Tb3+ is illustrated and discussed in detail.A novel white long persistent phosphor of Y3Al2Ga3O12:Tb3+ was prepared by the soft chemical method. Y3Al2Ga3O12:Tb3+ presented a white long persistent luminescence when the doping concentration of Tb3+ was just 0.1% and the afterglow time was able to last more than 2 h. The persistent emission of Tb3+ in Y3Al2Ga3O12 consisted of all color emissions in the visible spectrum from an identical luminescent center (Tb3+); meanwhile, the white-light color won't vary as the afterglow time goes on. The mystery behind this phenomenon was studied deeply including trap depths, distribution and types. The trap depths was calculated from 0.65 to 1.15 eV by the initial rise method analysis, highly corresponding to the ideal energy for trapping and releasing at room temperature. What's more, the estimated trap structure was proved to be a continuous trap distribution by varying the thermal cleaning temperature. The persistent luminescence mechanism of Y3Al2Ga3O12:Tb3+ was illustrated and discussed in detail on the basis of the experimental results. This work provides a promising approach for the development of white long persistent phosphor.

A series of Eu2+ and Mn2+ co-doping Sr3GdLi(PO4)3F phosphors have been synthesized through high temperature solid state reaction. Eu2+ single doped Sr3GdLi(PO4)3F phosphors have an efficient excitation in the range of 230–430 nm, which is in good agreement with the commercial near-ultraviolet (n-UV) LED chips, and gives intense blue emission centering at 445 nm. The critical distance of the Eu2+ ions in Sr3GdLi(PO4)3F is computed and demonstrated that the concentration quenching mechanism of Eu2+ is mostly caused by the dipole-dipole interaction. By co-doping Eu2+ and Mn2+ ions in the Sr3GdLi(PO4)3F host, the energy transfer from Eu2+ to Mn2+ that can be discovered. With the increase of Mn2+ content, emission color can be adjusted from blue to white under excitation of 380 nm, corresponding to chromatic coordinates change from (0.189, 0.108) to (0.319, 0.277). The energy transfer from Eu2+ to Mn2+ ions is proven to be a dipole-dipole mechanism on the basis of the experimental results and analysis of photoluminescence spectra and decay curves. This study infers that the obtained Sr3GdLi(PO4)3F:Eu2+, Mn2+ phosphors may be a potential candidate for n-UV LEDs.

Multifunction and high integration has always been a goal worth pursuing when important breakthroughs of multidisciplinary researches in the fields of thermo-luminescent, opto-electronic, photo-magnetic interaction, etc., are emerged. Other significant considerations for a multifunctional strategy proposed in a single-material system are low-cost components and processing, universal applicability, and widespread popularity. Herein, we developed an all-purpose material with a tunable light emission property and controllable optoelectronic and optothermal response process. We showed a disappearance of emission behavior under the excitation of UV light by building a mid-gap host (Bi2O3) along with a rare earth (Sm3+) ion, with multiple energy level configurations, as an emission center. We also demonstrated that this scheme realized the successful imbedding of higher energy level Sm3+ into the conduction band and led to increased current under the excitation of visible light and the depopulated redistribution of the excited state level near the conduction band at higher temperatures. Thus, this phosphor is expected to open up the possibility of potentially free choice of light shielding, temperature sensing, and photodetection in a single-material system.

A series of novel red-emitting Na2Ca3 − xSi2O8:xEu3+ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na2Ca3Si2O8:Eu3+ were characterized. Na2Ca3Si2O8:Eu3+ with self-compensated and alkali metal ions charge compensated approaches (2Ca2+→Eu3+ + M+, M = Li+, Na+, K+) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y203S:Eu3+. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.

Here we report a series of multifunctional Cr3+-doped magnesium gallogermanate particles. Several minutes of ultraviolet (UV) light excitation can lead to strong near-infrared (NIR) long persistent luminescence (LPL) at 600–850 nm with a long lasting time of at least 25 h. After the disappearance of LPL, NIR photostimulated persistent luminescence (PSPL) can be rejuvenated repeatedly several times by an external photostimulus (visible or NIR light). Meanwhile, the material shows photochromic (PC) properties, i.e., the surface color can change reversibly between white/pale green and rosybrown with high fatigue resistance by alternating UV and visible light irradiation. When the temperature is increased to 300 °C, the induced rosybrown surface color can also be bleached. This new multifunctional material has potential applications in a wide range of fields, such as in vivo bio-imaging, optical information write-in and read-out media, erasable optical memory media and optical sensors. The continuous trap distribution and modulation were characterized. The optimum trap depth was determined to be 0.51–0.86 eV. In addition, we gained insight into the mechanism of multifunctional properties and the interconnection between them.

A series of Sr3Lu(PO4)3:Eu3+ phosphors were successfully prepared via the solid-state method, and their luminescence properties were investigated. The excitation and emission spectra show that this phosphor can be effectively excited by near ultraviolet (NUV) light, and produces strong and prevailing red emissions at 612 nm belonging to the 5D0→7F2 electric dipole transition. Eu3+ ion was heavy doped in Sr3Lu(PO4)3 host and the optimal concentration of Eu3+ was found as 0.8. The critical transfer distance of Eu3+ was determined to be 8.5 Å. The concentration quenching was demonstrated to be caused by the energy transfer among the nearest-neighbor ions in the Sr3Lu(PO4)3:Eu3+ phosphor. Under excitation of 394 nm, the integral emission intensity of Sr3Lu0.2(PO4)3:0.8Eu3+ is about 6 times that of Y2O3:Eu3+. The CIE color coordinates of Sr3Lu0.2(PO4)3:0.8Eu3+ was (0.636, 0.354) located in red region. In addition, good thermal stability was also identified in Sr3Lu0.2(PO4)3:0.8Eu3+ and its emission intensity was reduced to 88% of its initial value at 100 °C and 70% at 200 °C. The current research suggests that Sr3Lu(PO4)3:Eu3+ could be a promising red phosphor for white LEDs and display devices.

•Li2CO3 plays a critical role in producing persistent luminescence.•40 % excess of Li2CO3 makes the largest enhancement on persistent luminescence.•The optimal doping concentration of Eu2+ was experimentally to be 1mol %.•Possible mechanism for persistent luminescence was discussed.An orange emitting long persistent phosphor LiSr4(BO3)3:Eu2+ was prepared successfully using a conventional solid state reaction method. The luminescent and persistent luminescence properties were studied using fluorescence spectra, decay curves, persistent luminescence spectra and thermoluminescence (TL) glow curves. The effects on the fluorescence and persistent luminescence properties by the dosage of Li2CO3 were explored. The relationship between the Eu2+ contents and persistent luminescence properties were studied. The optimal doping concentration of Eu2+ was experimentally to be 1 mol%. The detailed processes and a possible mechanism were also discussed.

•A high color purity deep red emitting phosphor SrGe4O9:Mn4 + was prepared successfully.•The concentration quenching of Mn4 + mainly occurs due to electric multipolar interaction mechanism.•The fluorescence of Mn4 + in SrGe4O9 shows good thermal stability.•SrGe4O9:Mn4 + may be a potential red phosphor matching with blue LED for warm w-LEDs.The discovery of non-rare-earth doped oxide red phosphor, particularly excitable by light in the wavelength from 380 to 480 nm, is of great interest in the field of energy-efficient w-LED lighting. Here, we report a potential candidate of red phosphor for warm w-LEDs. Mn4 +-doped SrGe4O9 phosphors that show deep red emission upon blue excitation were prepared by a solid-state reaction route. The luminescent performance is characterized by steady-state photoluminescence (PL) spectra, fluorescence decay curves and temperature-dependent photoluminescence measurements. The concentration quenching phenomenon is clarified. The resistance of Mn4 + photoluminescence to thermal impact after a cycle experiment by heating and cooling the sample between 35 °C and 210 °C has also been studied. It proves that SrGe4O9:Mn4+ possesses good thermal stability. Based on configuration coordinate schematic diagram, the thermal quenching mechanism is discussed. It may be a potential red phosphor which is applied to the package of a blue LED for warm w-LEDs.

New non-rare-earth red phosphor BaGe4O9:Mn4+ was prepared successfully via the traditional solid state reaction method. The luminescent performance was investigated by the steady-state photoluminescence (PL) and temperature-dependent PL/decay measurements. The excitation band of BaGe4O9:Mn4+ phosphor covers a broad spectral region from 250 nm to 500 nm, which matches well with the commercial near-UV and blue LEDs. The concentration quenching of Mn4+ in BaGe4O9:Mn4+ occurs at a low content of 0.5% due to the dipole–dipole interaction. We gained insight into the temperature-dependent relative emission intensity of BaGe4O9:Mn4+ phosphor, and determined the luminescence quenching temperature and the activation energy for thermal quenching (∆E) to be ~150 K and ~0.17 eV, respectively.

Photochromic materials have attracted increasing interest as optical switches and erasable optical memory media. Here, we report on a novel reversible colorless-cyan photochromic powder material Sr3YNa(PO4)3F:Eu2+. The photochromic properties including coloring and bleaching are characterized by reflectance spectra after the powder is irradiated by different wavelengths of light for different irradiation times or processed by thermal treatment. The results show that it can be colored by short wavelength light (200–320 nm) and bleached by longer wavelength light (320–800 nm) or thermal treatment at 240 °C. The optimal doping concentration of Eu2+ is determined to be about 0.5 mol%. It shows high fatigue resistance in photochromism performance. Electrons in 4f ground levels excited by short wavelength irradiation to higher 5d states of Eu2+ and then captured by traps are responsible for the coloring process. Correspondingly, the release of trapped electrons from two kinds of traps with different depths causes the initially fast and later slow bleaching processes. The critical role of charge carrier motions between two different traps is discussed. The colorless-cyan photochromism can be explained semi-quantitatively on the basis of obtained results. A tentative model was proposed to illustrate the PC mechanism.

The pink persistent phosphor La3GaGe5O16:Pr3+ was prepared successfully via a traditional solid state reaction method. In this paper, the La3GaGe5O16 host is proved to be a new self-activated luminescent host lattice on the basis of excitation and emission spectra. The La3GaGe5O16 host gives a blue emission under excitation at 260 nm. In the emission spectrum for La2.99GaGe5O16:0.01Pr3+, two dominant peaks arise from a 3P0 → 3H4 transition in the blue region and a 1D2 → 3H4 transition in the red region, respectively. However, concentration quenching of Pr3+ in La3GaGe5O16:Pr3+ occurs at a low Pr3+ content of 0.02 in this work, which is mainly due to a dipole–dipole interaction. La3GaGe5O16:Pr3+ phosphors exhibit pink persistent luminescence after short UV-irradiation. The optimal concentration of Pr3+ for the long persistent luminescence in the La3GaGe5O16 host is experimentally about 0.01. The long persistent luminescence of La3GaGe5O16:Pr3+ is discussed in accordance with the afterglow decay and thermoluminescence analysis. A model is proposed based on the experimental results to explain the mechanisms of the photoluminescence and afterglow phenomenon.

New non-rare-earth red phosphor La3GaGe5O16:Mn4+ was prepared successfully via the traditional solid state reaction method. In this paper, we reported this red phosphor La3GaGe5O16:Mn4+ as a promising red converter for warm white light under excitation at UV or blue light. The phase and microstructure of this red phosphor were characterized with aids of the XRD and SEM; the luminescent performance was investigated by the diffuse reflection spectra, photoluminescence (PL) spectra, and temperature-dependent PL/decay measurements. The excitation band of La3GaGe5O16:Mn4+ phosphor covers a broad spectral region from 250 nm to 500 nm, which match well with the commercial near-UV and blue LEDs and can give intense bright red emission. The crystal field strength (Dq) and the Racah parameters (B and C) are calculated to evaluate the nephelauxetic effect of Mn4+ suffering from the La3GaGe5O16 host. The concentration quenching of Mn4+ in La3GaGe5O16:Mn4+ occurs at a low content of 0.25% due to the dipole–dipole interaction in this work. We gained insight into the temperature-dependent relative emission intensity of La3GaGe5O16:0.25% Mn4+ phosphor, and we also reported the luminescence quenching temperature and the activation energy for thermal quenching (ΔE). In future, WLEDs will be made when this red phosphor was applied to the package of a UV/blue LED chip and YAG:Ce.

•We investigate the energy transfer from the host to activators Tb3+ ions and concentration quenching for CdGeO3:Tb3+.•CdGeO3:Tb3+ gives a green long persistent luminescence.•We compared it with the commercial phosphor SrAl2O4:Eu2+, Dy3+.A novel green persistent phosphor CdGeO3:Tb3+ is prepared successfully via the traditional solid state reaction method. The phase purity and morphology of CdGeO3:Tb3+ samples are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.Energy transfer from host to activators Tb3+ occurs efficiently under excitation into the host absorption. CdGeO3:Tb3+ phosphors show a bright green luminescence under excitation with 311 nm. However, concentration quenching of Tb3+ in CdGeO3:Tb3+ occurs at a low content of 0.01 in this work. After the short UV-irradiation, CdGeO3:Tb3+ phosphors present excellent long persistent luminescence at room temperature. The optimal doping concentration of Tb3+ for the long persistent luminescence is about 0.005. The persistent luminescence mechanism of CdGeO3:Tb3+ is illustrated and discussed in detail on the basis of the experimental results.

•The phosphors show emitting from Ce3+ and Tb3+ with excitation wavelength of Ce3+.•There is high transfer efficiency with the maximal value 48.2% from Ce3+ to Tb3+.•The energy transfer mechanism from Ce3+ to Tb3+ is dipole–dipole interaction.A series of Ce3+ or Tb3+ doped and Ce3+/Tb3+ co-doped CaMgP2O7 phosphors were prepared by the solid state reaction method. The fluorescence and energy transfer property of samples were studied in details. CaMgP2O7:Ce3+, Tb3+ shows both an ultraviolet (UV) emitting (300–450 nm) from Ce3+ and a yellowish-green emitting (543 nm) from Tb3+ with considerable intensity under UV excitation (278 nm). The energy transfer mechanism from Ce3+ to Tb3+ ions was proved to be dipole–dipole interaction. The Ce3+ and Tb3+ co-doped CaMgP2O7 phosphors are potential UV-convertible candidates with green light emitting in UV-LEDs for the high efficient energy transfer from Ce3+ to Tb3+ ions.

•Y2WO6: Sm3+ is a single-phase, color-tunable, broadband-excited white light-emitting phosphor.•Energy transfer from the host to Sm3+ is mainly performed by exchange interact.•The chromaticity coordinates and color temperature can be tuned by changing the doping concentration of Sm3+.Un-doped and Sm3+ doped Y2WO6 were synthesized with solid state reactions. X-ray diffraction measurements show that all the samples present single-phase Y2WO6. The combination of blue emission in a broad band from the host and several groups of emission lines in yellow, orange, and red spectral region results in a desired white light. The chromaticity coordinates and color temperature can be tuned by changing the doping concentration of Sm3+. The mechanisms of energy transfer were analyzed. The present results prove Sm3+ doped Y2WO6 is a promising single-phase, color-tunable, broadband-excited white light-emitting phosphor based on AlGaN-based ultraviolet light-emitting diodes.

•The persistent luminescence in CaAl2Si2O8:Eu2+,R3+ was reported.•CaAl2Si2O8:Eu2+,Pr3+ shows the best performance.•All the tested R3+ codopants have a positive influence on the afterglow intensity.We investigated the persistent luminescence in europium-doped CaAl2Si2O8 upon codoping with auxiliary rare earth ions (Pr3+, Nd3+, Dy3+, Ho3+ and Er3+). The persistent phosphors were synthesized via a solid-state reaction method under flowing N2+H2. Under UV irradiation, broad-band emission persistent luminescence located at 430 nm was observed in all the phosphors at room temperature. The effects of auxiliary rare earth ions on CaAl2Si2O8:Eu2+ were discussed according to the decay curves and thermoluminescence spectra. Although all the selected codopants can improve the performance of CaAl2Si2O8:Eu2+, CaAl2Si2O8:Eu2+,Pr3+ shows the best performance.

The blue emitting long persistent phosphor (LPP) Li2ZnGeO4 and green emitting LPP Li2ZnGeO4:Mn2+ were newly prepared by a high temperature solid-state reaction method. The blue and green afterglow with duration of 5 and 8 h were confirmed to originate from host emission and d–d transitions of Mn2+ ions, respectively. The density of traps with suitable depth was significantly increased with the incorporation of Mn2+ ions. The energy transfer from host emission to Mn2+ ions was observed. The motion of charge carriers and a possible LAG mechanism based on a tentative model were illuminated and discussed in detail.

Stoichiometric phosphors LiGd1−xEux(PO3)4(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO3)4. Eu3+ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state 5D0 to ground states 7F1 and 7F2, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu3+ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu3+ doped samples. Present research indicates that LiGd1–xEux(PO3)4 is a promising phosphor for white light-emitting diodes.

•The persistent luminescence in Ca3−xMg3(PO4)4:xEu2+ was reported.•Ca2.99Mg3(PO4)4:0.01Eu2+shows the best performance.•An energy level scheme was depict to elucidate the trapping and detrapping processes.Ca3−xMg3(PO4)4:xEu2+ persistent phosphors were successfully synthesized by solid-state reaction method. The persistent phosphors were investigated by XRD, diffuse reflectance, photoluminescence, persistent luminescence and thermoluminescence spectra. When irradiated in advance with ultraviolet light, this phosphor shows a broad-band persistent luminescence located at ∼433 nm at room temperature. The effects of the concentration of Eu2+ ions on the photoluminescence as well as persistent luminescence of Ca3−xMg3(PO4)4:xEu2+ were investigated. An energy level scheme was constructed to convey reasonable trapping and detrapping processes in the material.

•Zn2GeO4:Bi3+ phosphors were synthesized by solid-state reaction method.•The photoluminescence and persistent luminescence of Zn2GeO4:Bi3+ were investigated.•The photoluminescence and persistent luminescence mechanism of Zn2GeO4:Bi3+ was illustrated in detail.Bi3+-doped Zn2GeO4 were prepared by the high temperature solid-state reaction method. The phase purity and crystallinity of Zn2GeO4:Bi3+ samples were characterized by X-ray diffraction (XRD). The Photoluminescence and persistent properties of Zn2GeO4:Bi3+ phosphors were investigated through the excitation spectra, the emission spectra, the persistent luminescence, the persistent decay curves and thermoluminescence spectra. Excitation into the host absorption, Zn2GeO4:Bi3+ gives a blue broadband emission; a bluish-green emission of Zn2GeO4:Bi3+ is obtained for the direct excitation of Bi3+ under 300 nm excitation. Zn2GeO4:Bi3+ shows a weak persistent luminescence after irradiation by 254 nm UV light for 3 min. The photoluminescence and persistent luminescence mechanism of Zn2GeO4:Bi3+ were discussed in detail.

•The photoluminescence of R3+ ions (R = Eu, Sm, Dy, Tb and Pr) doped BaZrSi3O9 were studied.•The long afterglow with different color from R3+ ions were observed for the first time.•The energy transfer from the host to the activators was confirmed.•The mechanism of long afterglow for R3+ ion doped BaZrSi3O9 was discussed in detail.Undoped and R3+ ions (R = Eu, Sm, Dy, Tb and Pr) singly doped BaZrSi3O9 phosphors were synthesized by a traditional solid state reaction method. All samples were studied by X-ray diffraction, photoluminescence spectra, afterglow decay curves, long persistent luminescence (LPL) spectra and thermoluminescence (TL) glow curves. The different characteristic emissions and LPL from these R3+ ions were obtained by the same UV excitation. These phenomena were derived from the energy transfer that originates from BaZrSi3O9 host. The nature of trapping centers was studied with TL glow curves. The incorporation of R3+ ions into host lattice produced some new traps. Accordingly, the mechanism of long afterglow in BaZrSi3O9:R3+ was also discussed.

•Known Eu2+-activated phosphate persistent phosphors are listed.•The influence of codopants is compared with aluminates and silicates.•The concentration quenching of persistent luminescence is discussed.Recently, as a novel class of persistent phosphors, Eu2+-activated phosphate persistent phosphors have received considerable attention. In this review, we focus on new reported phosphate persistent phosphors. Their wavelength maximum, trap filling source, optimal codopant, etc., are compared. Furthermore, the mechanism behind this phenomenon, including energy level scheme, the influence of codopant and concentration quenching are discussed.

•A novel orange emitting long afterglow phosphor Ca3Si2O7:Eu2+ was synthesized successfully.•The orange afterglow can be greatly enhanced by co-doping with Tm3+, Dy3+ and Er3+ ions.•The details of influence on afterglow by Tm3+, Dy3+ and Er3+ were studied.•Accordingly, the afterglow and enhancement mechanism was discussed in brief.A novel orange emitting long afterglow phosphor Ca3Si2O7:Eu2+ was prepared successfully via a traditional high temperature solid-state reaction method. The co-doping of Tm3+, Dy3+ and Er3+ ions into Ca3Si2O7:Eu2+ separately can increase the trap density and/or produce new traps with suitable depth. They can enhance the brightness of afterglow and prolong the afterglow duration significantly. The duration of Eu2+ solely doped and Eu2+, Tm3+ co-doped Ca3Si2O7 phosphors can last 100 s and more than 15 min, respectively. Both the samples co-doped by Dy3+ and Er3+ can last more than 10 min. The mechanism of afterglow was discussed briefly.

•ZnB2O4:Bi3+ is an effective purplish blue phosphor.•ZnB2O4:Gd3+ is an effective ultraviolet phosphor.•This work indicates that ZnB2O4 is a promising host for display applications.A series of Bi3+ and Gd3+ doped ZnB2O4 phosphors were synthesized with solid state reaction technique. X-ray diffraction technique was employed to study the structure of prepared samples. Excitation and emission spectra were recorded to investigate the luminescence properties of phosphors. The doping of Bi3+ or Gd3+ with a small amount (no more than 3 mol%) does not change the structure of prepared samples remarkably. Bi3+ in ZnB2O4 can emit intense broad-band purplish blue light peaking at 428 nm under the excitation of a broad-band peaking at 329 nm. The optimal doping concentration of Bi3+ is experimentally ascertained to be 0.5 mol%. The decay time of Bi3+ in ZnB2O4 changes from 0.88 to 1.69 ms. Gd3+ in ZnB2O4 can be excited with 254 nm ultraviolet light and yield intense 312 nm emission. The optimal doping concentration of Gd3+ is experimentally ascertained to be 5 mol%. The decay time of Gd3+ in ZnB2O4 changes from 0.42 to 1.36 ms.

•Novel Ca3WO6:Eu3+ phosphor has been synthesized by the solid-state reaction method.•Ca3WO6:Eu3+ is suitable for blue light wavelength conversion.•The co-doped effects of alkali-metal ions on the luminescence properties for Ca3WO6:Eu3+ phosphors are discussed.Novel Ca3WO6:Eu3+ phosphor has been synthesized with different Eu3+ doping concentrations through the solid-state reaction method, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectra and decay curve. The results of XRD and SEM show that all Ca3WO6:Eu3+ samples are single phase and have irregular morphology. In the excitation spectrum of Ca3WO6:Eu3+ phosphor, the broad excitation band centering at 310 nm is due to the combination of charge transfer from Eu3+ to O2− and W6+ to O2−. The intense red emission can be obtained under excitation into the 5D2 state with 465 nm, which corresponds to the emission wavelength from blue light-emitting diodes (LEDs). The co-doped effect of alkali-metal ions (Li+, Na+, and K+) on the luminescence behavior of Eu3+-doped Ca3WO6 has been discussed in this paper. The luminescence properties suggest that novel Ca3WO6:Eu3+ phosphor may be a potential red phosphor for white LEDs.

The Eu3+ doped MWO4 (M=Ca, Sr, Ba) phosphors were synthesized via high temperature solid state reaction. The crystal phases of these phosphors were identified by X-ray diffraction. Shifts of the peaks in the structure were observed when Ca2+ sites in the host were completely occupied by the Sr2+ ions or Ba2+ ions. As a result of this replacement, the charge-transfer (CT) band exhibited a blue shift from CaWO4: Eu3+ to SrWO4: Eu3+ and BaWO4: Eu3+. This blue shift could be interpreted with the decreases of the bond covalence between the ligands (L) and the central ion (M) in matrix. In this work, red afterglow originated from the 5D0–7FJ (J=0,1,2,3,4) transitions of Eu3+ could clearly be observed after samples were excited at 254 nm. The thermoluminescence (TL) spectra showed that there were five traps levels in CaWO4: Eu3+ sample and two traps levels in CaWO4: Eu3+ and CaWO4: Eu3+ samples, respectively. The possible explanation of this afterglow phenomenon was also discussed in detail.Highlights► The red afterglow of Eu3+ in MWO4 (M=Sr, Ba) matrix is first observed. ► The blue shift of the charge-transfer band appears and its proposed explanation is discussed. ► The feasible mechanism of the afterglow is presented.

The novel green light emitting phosphors Ca2SnO4:Tb3+ were synthesized via a traditional solid state reaction method. All as-prepared phosphors were studied systematically by X-ray diffraction, scanning micrograph images, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence glow curves. The cross-relaxation of two adjacent Tb3+ ions led to the main emission peaks locate at 483 and 545 nm under excitation of 255 nm. The CIE chromaticity coordinates are x=0.197 and y=0.279. The intensities of photoluminescence and afterglow are dependent on the concentration of Tb3+ ions. The optimal concentration of Tb3+ ions for the best afterglow characteristic was experimentally to be 0.1 mol%. After irradiation by 254 nm, the duration of afterglow can last more than 3 h. The mechanism of long afterglow in Ca2SnO4:Tb3+ is also discussed.Highlights► The photoluminescence properties of Ca2SnO4: Pr3+ was investigated systematically. ► The long afterglow was observed in Ca2SnO4: Pr3+ phosphor for the first time. ► The optimized concentration of Pr3+ ions was experimentally to be 0.3 mol%. ► The mechanism of long afterglow was discussed in detail.

A novel red light emission long persistent phosphor, Ca2SnO4:Pr3+, was prepared by a high temperature solid-state reaction method. All as-prepared phosphors were studied systematically by X-ray diffraction, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence (TL) glow curves. Four main emission peaks of afterglow spectrum locate at 496, 605, 625 and 658 nm corresponding to CIE chromaticity coordinates of x = 0.506, y = 0.355. The intensities of photoluminescence and the performance of afterglow are dependent on the concentration of Pr3+ ions. The traps with depth of 0.79–0.82 eV are the origination of long afterglow (LAG). The optimal concentration of Pr3+ ions for the best afterglow characteristic was experimentally to be 0.3 mol%. After irradiation by 254 nm, the duration of red afterglow can last about 20 min. The mechanism of LAG in Ca2SnO4:Pr3+ was also discussed in detail.Highlights► The photoluminescence properties of Ca2SnO4:Pr3+ was investigated systematically. ► The long afterglow was observed in Ca2SnO4:Pr3+ phosphor for the first time. ► The optimized concentration of Pr3+ ions of afterglow was experimentally to be 0.3 mol%. ► The mechanism of long afterglow was discussed in detail.

A novel Sm3+-doped CaO phosphor was synthesized by a traditional high temperature solid-state reaction method. The luminescence properties were studied and orange long afterglow was observed for the first time. The dependence of photoluminescence (PL) and long afterglow (LAG) properties on Sm3+ contents were investigated systematically. The optimal concentrations of Sm3+ ions for the best PL and LAG properties were experimentally to be 0.4 and 0.3 mol%, respectively. After irradiation by 254 nm for 3 min, the duration of orange afterglow can last nearly 40 min. The traps caused by the incorporation of Sm3+ ions are responsible for the generation of orange LAG. The mechanism of LAG was also illustrated briefly.

The red afterglow phosphors of CaWO4 doped with Eu3+, Zn2+ or (and) Si4+ were prepared by solid state reaction. All crystalline phases were identified by the X-ray powder diffraction (XRD). The photoluminescence spectra and decay curves as well as thermoluminecence (TL) curves of all samples were also investigated. In comparison to CaWO4:Eu3+ phosphor, the luminescence and afterglow properties could be improved greatly after being doped with Zn2+ or (and) Si4+ ions.Graphical abstractEmission spectra (λex = 254 nm) of Ca0.99WO4:Eu0.013+, Ca0.98WO4:Eu0.013+,Zn0.012+, Ca0.98WO4:Eu0.013+, Si0.012+ and Ca0.97WO4:Eu0.013+, Zn0.012+, Si0.012+ samples.Highlights► Co-doping Zn2+ and Si4+ ions in CaWO4: Eu3+ could enhance the intensity of the charge band of WO42−. ► Co-doping Zn2+ and Si4+ ions in CaWO4:Eu3+ could make the energy transfer from WO42− to Eu3+ more efficiently. ► Co-doping Zn2+ and Si4 in CaWO4:Eu3++ is beneficial for the improvement the afterglow property.

Highlights•Novel Zn3(BO3)2:Eu3+ phosphor has been synthesized by solid-state reaction method.•The co-doped effects of alkali-metal ions on the luminescence properties for Zn3(BO3)2:Eu3+ phosphors are discussed.•The volume compensation and the equilibrium of mole number can be taken into consideration by charge compensation (CC) approaches.A series of the Zn3(BO3)2:Eu3+ without or with alkali metal ions doping at a low sintering temperature were synthesized by the solid-state reaction method. The XRD pattern shows that all samples exhibit Zn3(BO3)2 crystalline phase. The samples co-doped with alkali metal ions have better crystallinity compared with the un-compensated ones. The different charge compensation approaches have no influence on the shape and position of the emission and excitation spectra. However, the luminescent intensity of samples has been obviously enhanced with different alkali metal ions co-doping. The introduction of Li+ can increase the red emission of Eu3+ compared with the others. Thus, the volume compensation and the equilibrium of mole number can be taken into consideration by charge compensated (CC) approaches.

A series white-amethyst photochromic materials, Ba5(PO4)3Cl:Eu2+,R3+ (R = Y, La–Nd and Sm–Lu) are synthesized. These materials are sensitive to electromagnetic waves from short UV to X-ray. The materials change their color from white to amethyst by short UV or X-ray irradiation. The photo-colored samples can be bleached by green light irradiation or heat treatment. A model that involves ionization of the 5d electron of Eu2+ to conduction band states and subsequent trapping by a positive lattice defect is proposed for the photochromism in these compounds.Graphical abstractHighlights► The material changes its body color upon short UV or X-ray irradiation. ► After green light irradiation or heat treatment the colored samples can be bleached. ► No degeneration was observed after many coloration ↔ bleaching processes. ► A model was proposed for the photochromism in this compound.

•The optimal concentration of Pr3+ ions in CaO was experimentally calculated to be 0.05 mol%.•The energy transfer process from host to Pr3+ ions was discussed.•The reddish orange emitting long afterglow that can last nearly 1 h was observed in CaO:Pr3+ for the first time.•The mechanism of long afterglow was discussed in detail.A novel reddish orange emitting long persistent phosphor CaO:Pr was prepared by a high temperature solid-state reaction method. All as-prepared phosphors were studied systematically by X-ray diffraction, photoluminescence (PL) spectra, decay curves, afterglow spectra and thermoluminescence (TL) glow curves. The intensity of PL and the performance of afterglow are dependent on the concentration of Pr3+ ions. The trap depth in the range between 0.5 and 0.7 eV is suitable for long afterglow (LAG). The optimal concentrations of Pr3+ ions for the best characteristic PL emission and afterglow were experimentally calculated to be 0.05 mol%. After irradiation by 273 nm for 3 min, the duration of reddish orange afterglow can last nearly 1 h. The decay processes and mechanism of LAG in CaO:Pr3+ were also discussed in detail.

A series of Eu3+–Sm3+ co-doped CaWO4 phosphors were synthesized by the high temperature solid-state method. The crystal structure of the obtained samples was identified by XRD, and the results showed that all the phases were indexed to scheelite structure. The effect of the doping concentration of Sm3+ on the luminescent properties of the obtained products was investigated, and the optimal Sm3+ concentration was experimentally determined to 0.5%. The photoluminescence properties indicate that there is an efficient energy transfers from Sm3+ to Eu3+. The energy-transfer process between Sm3+ and Eu3+ was also given. Red long afterglow originating from the 5D0–7FJ (J=0, 1, 2, 3, 4) transitions of Eu3+ was observed after samples were excited by 254 nm, and the duration of the optimal sample can last more than 35 min in dark with naked eyes. The proposed explanation for the afterglow property was also discussed.Highlights► The afterglow of Eu3+ and its enhancement by Sm3+ co-doping in CaWO4 is studied. ► An optimal Sm3+ doping concentration for the Eu3+ afterglow properties was found. ► The mechanism of energy transfer between Sm3+ and Eu3+ is presented, and the proposed cause of long afterglow was discussed.

The spectroscopic characterization of yttria, singly and doubly doped with Ln3+ (Ln=Sm, Eu, Dy, Er, Ho) and Bi3+ ions, is performed through excitation spectra, emission spectra and decay time measurements. The obtained spectroscopic data clearly indicate that energy transfer takes place from Bi3+ to Ln3+ ions. The energy transfer efficiency of Bi3+→Ln3+ and quantum efficiency of Ln3+ were calculated. Upon excitation of 370 nm (Bi3+ excitation band), the quantum efficiency of Ln3+ varies from ∼4% to ∼44%. The energy transfer efficiency increases continuously with increasing Ln3+ concentrations, whereas the variation of the quantum efficiency of Ln3+ is complicated. The quantum efficiency of Ln3+ is discussed in terms of electron transfer and cross relaxation.Highlights► Photoluminescence of Y2O3 doped with Sm, Eu, Dy, Er, Ho and/or Bi was reported. ► Energy transfer from Bi to Sm, Eu, Dy, Er and Ho was discussed. ► Lanthanides with lower reduction potentials greatly quench Bi3+ emission.

A series of Bi3+/Eu3+ singly and doubly activated Ca4YO(BO3)3 phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. Under UV excitation Bi3+ and Eu3+ show a high light output. Ca4YO(BO3)3:Eu3+ has potential application as a phosphor for fluorescent lamps. The luminescence of Bi3+ and Eu3+ in Ca4YO(BO3)3 resembles more that in the rare earth oxides than that in borates. The free oxygen ion in the host lattice, which is not bonded to any boron ions seems to be responsible for that. In this host lattice energy migration between linear Eu3+ chains occurs. The emission of Bi3+ is completely quenched when Eu3+ is co-doped. A model was proposed to explain it.Highlights► The photoluminescence of Bi3+ and Eu3+ singly/doubly doped Ca4YO(BO3)3 was reported. ► Ca4YO(BO3)3:Eu3+ is a promising lamp phosphor. ► The quenching of Bi3+ at Eu3+ presenting was attributed to electron transfer.

Aluminate phosphors SrMgAl10O17 codoped with Eu2+ and Mn2+ ions were prepared by solid-state reaction. The phase structure and photoluminescence properties of the as-prepared phosphors were characterized by powder X-ray diffraction, photoluminescence excitation and emission spectra. Upon excitation of UV light, two broad emission bands centered at 470 and 515 nm were observed, and they were assigned to Eu2+ and Mn2+ emissions, respectively. The emission color of the phosphors can be tuned from blue to cyan and finally to green by adjusting the concentration ratios of Eu2+ and Mn2+. Effective energy transfer occurs from Eu2+ to Mn2+ in the host due to the spectral overlap between the emission band of Eu2+ and the excitation bands of Mn2+. The energy transfer mechanism was demonstrated to be electric dipole–quadrupole interaction. The energy transfer efficiency and critical distance were also calculated. The phosphors exhibit strong absorption in near UV spectral region and therefore they are potentially useful as UV-convertible phosphors for white LEDs.Highlights► The strong absorption of phosphors matches well with the emission band of UV LED. ► The energy transfer from Eu2+ to Mn2+ in SrMgAl10O17 was investigated in detail. ► The emission color can be tuned by adjusting the content of Eu2+ and Mn2+. ► Two methods were employed to calculate the critical distance of energy transfer.

The europium (Eu2 +) and dysprosium (Dy3 +) codoped melilite (Sr2MgSi2O7) long afterglow phosphors are synthesized with H3BO3 and Li2CO3 fluxes, respectively. The XRD analysis demonstrates similar crystal structure and crystal size of the samples. The SEM presents a better crystallization of samples with flux, other than the one without flux. The excitation and emission spectra of the samples are similar but the decay processes of the afterglow are different. The afterglow properties are enhanced by H3BO3 while they are suppressed by Li2CO3, due to the different concentrations and depths of traps. The sample without flux has a low trap concentration because of the greater surface. Li+ ions reduce the concentration of Sr2 + vacancies and then the trap depth becomes smaller. B3 + ions break the potential balance in oxygen vacancies then the attraction to trapped electron is enhanced.Highlights► Two opponent influences of fluxes on luminescent properties are investigated. ► Smooth surface on samples are beneficial to the luminescence. ► A substitution of B3 + for Si4 + deepens the trap depth and prolongs the afterglow.

A series of Eu3+ activated K3Y1−xEux(PO4)2 phosphors were synthesized by the solid-state reaction method. The structures and photoluminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic K3Y(PO4)2 or K3Eu(PO4)2. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370–410 nm) light. The orange emission from transition 5D0–7F1 is dominant, and the peak value ratio of 5D0–7F1/5D0–7F2 is 1.44. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x=0.63, y=0.36), which is due to the 5D0–7FJ transitions of Eu3+ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The absence of concentration quenching of Eu3+ was observed in K3Y1−xEux(PO4)2. K3Eu(PO4)2 has potential application as a phosphor for white light-emitting diodes.Highlights► The photoluminescence properties of K3Eu(PO4)2 were investigated in detail. ► We demonstrated that Eu3+ activated phosphor based on NUV LED should be heavy doped. ► The energy levels 5L6,7 and 5GJ of Eu3+ form a quasi-broad band in our phosphor.

In order to develop high efficiency red emitting phosphors, Ca0.76MoO4: Eu0.243+ samples are investigated via sol–gel and solid state reaction. The XRD analysis reveals that both methods can synthesize phosphors with tetragonal CaMoO4 phase successfully. Smaller crystal size of samples prepared by sol–gel can be observed, and the grain size of these samples are around 100–200 nm, which is also smaller than the one prepared by solid state reaction. All phosphors present a red emission at 616 nm wavelength and one sol–gel synthesized sample exhibits the strongest emission intensity because of the higher quantum efficiency. It is attributed to the removal of lattice defects by sol–gel, in which way luminescent efficiency is enhanced. This can be reflected by the longer fluorescent lifetime of phosphors.

The Ca2Al2SiO7 samples doped with Ce3+ and Eu2+ are synthesized via a high temperature solid-state reaction. Ca2Al2SiO7: Ce3+ emits a strong UV–violet emission while Ca2Al2SiO7: Eu2+ emits a blue–green emission. The Stokes shift of the latter is greater due to a stronger crystal repulsion from ligands to Eu2+ ions. Ca2Al2SiO7: Ce3+ exhibits a stronger initial intensity and longer duration of afterglow due to the higher liberated probability of the trapped carriers. The thermoluminescence curves reveal that at least three traps exist in the phosphors. Ca2+ vacancies may enhance the electron trapping and then lead to a stronger afterglow. A possible explanation will be provided.Highlights► Long afterglow phenomenon of Eu2+ in Ca2Al2SiO7 is first reported in the present work. ► Thermoluminescence of both Ce3+ and Eu2+ in Ca2Al2SiO7 is investigated in detail. ► Crystal field theory is employed to explain the Stokes shift.

In the present paper, phosphors with the composition Y3−x−yAl5O12:Bi3+x, Dy3+y were synthesized with solid state reactions. The luminescence properties of Bi3+ and Dy3+ in Y3Al5O12(YAG) and the energy transfer from Bi3+ to Dy3+ were investigated in detail. Bi3+ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states 3P0, 1 to ground state 1S0. Dy3+ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state 4F9/2 to ground states 6H15/2 and 6H13/2. The co-doping of Bi3+ enhances the luminescent intensity of Dy3+ by ∼7 times because Bi3+ can transfer the absorbed energy to Dy3+ efficiently. The mechanism of energy transfer was also discussed.Highlights► Energy transfer from Bi3+ to Dy3+ was observed in Bi3+ and Dy3+ co-doped Y3Al5O12. ► Luminescent intensity of Dy3+ can be enhanced by ∼7 times by co-doping of Bi3+. ► Mechanism of energy transfer from Bi3+ to Dy3+ was discussed.

A series of phosphors with the composition Y3−xMnxAl5−xSixO12 (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn2+ and Si4+ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn2+ in Y3Al5O12 emits yellow–orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn2+ and Si4+ co-doped samples emit yellow–orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18 min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content.Research Highlights►Mn2+ and Si4+ co-doped Y3Al5O12 phosphors emit yellow–orange light in a broad band. ►These phosphors have longer persistent luminescence. ►There are two kinds of different traps showed by thermoluminescence in the phosphors.

Mn2+ is an excellent luminescent ion with variable color from green, yellow to red in different hosts and has been widely utilized in recent years. The luminescent intensity of Mn2+ in many hosts is so low that the correlative application is restricted. In the present paper, two methods, i.e. employing a charge compensator and introducing a sensitizer, were adopted to enhance the luminescence of Mn2+ in Y3Al5O12 (YAG). By employing Si4+ as a charge compensator, the doping content of Mn2+ (x) in Y3MnxAl5−2xSixO12 can be lifted up to 0.4. Mn2+ in YAG emits orange light in a broad band. The peak wavelength shifts from 586 to 593 nm with the increasing x. The luminescent intensity of Mn2+ reaches its maximum when x = 0.1. Co-doping Tb3+ into Mn2+ doped YAG, the sensitization effect of Tb3+ on Mn2+ was observed clearly. The resonance energy transfer from Tb3+ to Mn2+ occurs because there is a well overlapping between emission spectrum of Tb3+ and excitation spectrum of Mn2+. A reasonable explanation for the sensitization effect of Tb3+ on the luminescence of Mn2+ was brought forward.Graphical abstract▶ Tb3+ in YAG can emit two groups of lights which correspond to the transitions from 5D3 and 5D4 to 7FJ (J = 6, 5, 4, 3), respectively. Mn2+ in YAG has several excitation bands corresponding to the transitions from ground state 6A1 (6S) to excited states 4T2 (4G), 4A1 (4G), 4T2 (4D), 4E (4D), 2A1 (4D), and so on. From above figure, the transition of Mn2+ from 6A1 (6S) to 4E (4D) or 2A1 (4D) has equal energy with the transition of Tb3+ from 5D3 to 7F5, so does the transition of Mn2+ from 6A1 (6S) to 4T2 (4G) with the transition of Tb3+ from 5D4 to 7F6. The perfect energy matching between the emission of Tb3+ and the absorption of Mn2+ results in the occurrence of the energy transfer from Tb3+ to Mn2+ which enhances the luminescence of Mn2+ in YAG remarkably.Highlights► The solubility of Mn2+ in Y3MnxAl5−2xSixO12 can be lifted up when Si4+ exists as a charge and volume compensator. ► Mn2+ in Y3MnxAl5−2xSixO12 emits broadband orange light (peak wavelength varies from 586 nm to 593 nm). ► Tb3+ in phosphors Y3−yTbyMnxAl5−2xSixO12 can enhance the luminescence of Mn2+ remarkably. The energy transfer from Tb3+ to Mn2+ occurs and the reasonable explanation is given out.

Eu3+ doped ZnB2O4 without or with different charge compensation (CC) approaches (co-doping Li+, Na+, K, decreasing the content of Zn2+) were prepared by solid state reactions. The phosphors can strongly absorb 393 nm ultraviolet (UV) light which is coupled well with the emission of currently used InGaN-based near UV light emitting diodes (LEDs) and emit red light with a good color purity. The luminescent intensity of phosphors can be remarkably enhanced with any of CC methods. However, the shape and position of excitation and emission spectra keep unchanged. The introduction of Li+ can enhance the red emission intensity of Eu3+ by ∼4 times with the optimal effect. Red emission of Eu3+ can also be enhanced with the other three CC approaches but the effects are not as good as Li+ because the volume unbalance in Li+ compensation approach is the smallest while net positive charge was offset. The results of this work suggest that volume compensation and equilibrium of mole number should also be taken into account when a CC approaches is selected.Highlights► The introduction of Li+ in Eu3+ doped ZnB2O4 can enhance the red emission intensity of Eu3+ by ∼4 times. ► Volume compensation should also be taken into account when a charge compensation method is selected. ► The emission intensity of Eu3+ increases with the increasing crystallinity of the host.

The Sr1.99MgSi2O7: Eu2+0.01, and Sr1.97MgSi2O7: Eu2+0.01, R3+0.02 (R: Dy, Er) are synthesized via high temperature solid-state reaction. The sample without codoping shows the highest luminescent efficiency, leading to the strongest emission intensity. Both Dy3+ and Er3+ enhance the afterglow properties. Compared with Dy3+, sample doped with Er3+ shows a longer afterglow duration because of a deeper trap and it may be the optimum codopant for Sr2MgSi2O7: Eu2+ long afterglow phosphors.

A series of Eu3+ activated Li6Y1−xEux(BO3)3 (0.05 ⩽ x ⩽ 1) phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic Li6Gd(BO3)3. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370–410 nm) light. The red emission from transition 5D0→7F2 is dominant. The emission spectra exhibit strong red performance (CIE chromaticity coordinates: x = 0.65, y = 0.35), which is due to the 5D0−7FJ transitions of Eu3+ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The concentration quenching occurs at x ≈ 0.85 under near UV excitation. Li6Y(BO3)3:Eu3+ has potential application as a phosphor for white light-emitting diodes.Highlights► The photoluminescence properties of Li6Y(BO3)3:Eu were investigated in detail. ► The high quenching concentration mechanism was discussed. ► Demonstrated that Eu3+ activated phosphor based on NUV LED should be heavy doped. ► The energy levels 5L6,7 and 5GJ of Eu3+ form a quasi-broad band in our phosphor.

The long afterglow phosphors Sr1.97−xBaxMgSi2O7:Eu2+0.01, Dy3+0.02 (x=0, 0.4, 0.8, 1.2, 1.6 and 1.97) were synthesized via high temperature solid-state reaction. The phase identification reveals that the crystal plane spacing becomes greater with the decrease in the Sr/Ba ratio. Phase transition occurs when x=1.97. A nonlinear relationship between the emission peak and the crystal plane spacing is obtained with the decrease of the Sr/Ba ratio. This ascribes to the splitting of the 5d level of the Eu2+ and the change of the crystal field strength. The duration of the afterglow becomes shorter with the decrease of the Sr/Ba ratio. It may ascribe to deeper trap depth, lower trap concentration and the embarrassment of the transfer of carriers.Highlights► Tunable luminescent color has been achieved by adjusting the Sr/Ba ratio. ► Crystal field theory is used to explain the mechanism of the changing wavelength. ► Shortened afterglow duration with increasing Sr/Ba ratio due to the change of traps.

In this work, we report the high temperature solid-state synthesis of red phosphors Sr2MgSi2O7: Eu3+ with various Eu3+ concentrations. Their luminescent properties at room temperature are investigated. The X-ray diffraction patterns indicate that the red phosphors powder conforms to the tetragonal Sr2MgSi2O7. Impurity structure appears when more than 20% Eu3+ is doped. The samples show a strong emission line at 615 nm and the intensity increases with the increase of Eu3+ concentration until concentration quenching occurs. Charge compensation assists in the reduction of the impurity structure and vacancies; hence the luminescent intensity is enhanced. The decay measurement indicates that the lifetime of Eu3+ emission is about 2–3 ms. Some of the Eu3+ can be reduced to Eu2+; this is also discussed.

Sr2MgSi2O7:Eu2+, Dy3+ (SMED) and Ba2MgSi2O7:Eu2+, Dy3+ (BMED) were synthesized with the solid-state reaction. The SMED shows long afterglow while the afterglow of BMED is not visible at room temperature. When the environmental temperature is 150 °C, the afterglow of SMED is not obvious while the BMED shows the long afterglow. The decay curves measured at different temperatures conform to this phenomenon. It ascribes to the different trap depths of different samples. The thermoluminescence (TL) curves of SMED peaks at 80 °C. BMED has two TL peaks peaking at about 80 and 175 °C respectively. The low temperature peak is weak and its density is small. The high-temperature peak reveals that one trap of BMED is deeper than the one of SMED. The afterglows of the phosphors strongly depend on the environmental temperature since the lifetime of the trapping carriers is temperature-dependence. BMED is a potential optimum long afterglow phosphor for the purpose of high-temperature application.

The M2MgSi2O7: Eu2+, Dy3+ (M: Sr, Ca) long afterglow phosphors are investigated by substituting the Ho3+ ions for the Dy3+ ions. The emission intensity is about 3 times and 30% enhanced with this substitution in the Sr2MgSi2O7 and Ca2MgSi2O7 host, respectively. The emissions of the europium ions and the holmium ions are observed. Both emissions attribute to the 5d → 4f transition, indicating that some of the Ho3+ ions are reduced to the Ho2+ ions. The Ho3+ ions or the Dy3+ ions aggregate with the cation and the oxygen vacancies forming the traps. The traps induced by the clusters with Ho3+ ions are shallower than those induced by the clusters with Dy3+ ions. The traps’ concentration of the Ho3+ cluster is lower. The probability of retrapping of the released carriers decreases with the Ho3+ ions co-doping. The combination effect of the shallow traps and the non-retrapping process gives rise to a greater intensity of the initial emission and a shorter duration of the afterglow.

The modification effect of the doping of Yb3+ ions, as an auxiliary activator, onto the luminescent properties of SrAl2O4:Eu2+, Dy3+ phosphor was studied for the first time. The phosphorescent nanoparticles were prepared by the combustion method. The experimental results indicate that the appropriate doping of Yb3+ ions largely improves phosphorescence of the phosphors with more intense luminescence, higher brightness, and no change in emission spectrum peaked at 513 nm. Meanwhile the decay speed of the phosphor nanoparticles rises increasingly with the doping ratio of Yb3+ ions, whereas an excessive Yb3+ ions doping leads to the disappearance of the pure monoclinic phase of SrAl2O4 and the appearance of the weak diffraction lines of the YbAlO3 phase. The phosphorescent mechanism of the phosphors could be well understood based on the hole, thermally released from the trap levels of Dy3+ and Yb3+.

•The phosphors were synthesized via the solid state reaction at 800 °C.•Sr3Al2O5Cl2:Pr3+ phosphor gives a blue green afterglow luminescence.•Sr3Al2O5Cl2:Eu2+, Pr3+ phosphor present an orange red afterglow luminescence, lasting for 300 min.The Sr3Al2O5Cl2:Eu2+, Pr3+ phosphor has been synthesized via high temperature solid state reaction. The X-ray powder diffraction confirms that the obtained samples are pure orthorhombic Sr3Al2O5Cl2 phases, with a space group of D24-P212121. Blue green emission is observed when the sample is doped with Pr3+ ions and an orange red emission with Eu2+ ions doping. Both of the samples show obvious afterglow emission. The intensity and lifetime of such afterglow can be substantially enhanced in the case of Pr3+-Eu2+ co-doped, whose afterglow can last for approximately 300 min in the dark and the intensity is five times higher than the sample single doped with Eu2+. According to the thermoluminescence glow curves, the trap depth of these double-doped samples is about 0.95 eV, which is suitable for the generation of afterglow luminescence. And Pr3+ ions help to enhance the traps concentrations and modify the trap depth, which contributes to prolong the afterglow duration and increase the afterglow intensity of the phosphors. Finally, a feasible explanation of this afterglow generation is also discussed in this work.

A series of Eu2+ and Tb3+ doped Sr3YNa(PO4)3F phosphors have been synthesized via a high temperature solid state reaction method. Eu2+ activated Sr3YNa(PO4)3F phosphors can be efficiently excited by light in the range of 220–420 nm, which matches well with the commercial n-UV LEDs, and show intense blue emission centered at 456 nm. The optimal doping concentration of Eu2+ is determined to be 1 mol%. The concentration quenching mechanism of Eu2+ in SYNPF host is mainly attributed to the dipole-dipole interaction. Energy transfer from Eu2+ to Tb3+ is observed when Eu2+ and Tb3+ are co-doped into Sr3YNa(PO4)3F host. Under excitation of 380 nm, the emission color can be varied from blue to green along with the increase of Tb3+ doping concentration. Based on decay curves, the energy transfer from the Eu2+ to Tb3+ ions is demonstrated to be a dipole–dipole mechanism. According to thermal quenching study by yoyo experiments of heating-cooling, Sr3YNa(PO4)3F:Eu2+, Tb3+ shows good thermal stability. The thermal quenching mechanism is also discussed. The results indicate that as-prepared samples might be of potential application in w-LEDs

A series of Bi3+/Eu3+ singly and doubly activated Ca4YO(BO3)3 phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. Under UV excitation Bi3+ and Eu3+ show a high light output. Ca4YO(BO3)3:Eu3+ has potential application as a phosphor for fluorescent lamps. The luminescence of Bi3+ and Eu3+ in Ca4YO(BO3)3 resembles more that in the rare earth oxides than that in borates. The free oxygen ion in the host lattice, which is not bonded to any boron ions seems to be responsible for that. In this host lattice energy migration between linear Eu3+ chains occurs. The emission of Bi3+ is completely quenched when Eu3+ is co-doped. A model was proposed to explain it.Highlights► The photoluminescence of Bi3+ and Eu3+ singly/doubly doped Ca4YO(BO3)3 was reported. ► Ca4YO(BO3)3:Eu3+ is a promising lamp phosphor. ► The quenching of Bi3+ at Eu3+ presenting was attributed to electron transfer.

Inorganic photochromic materials have attracted growing attention in recent years. Here, a reversible white-purple photochromic powder material Sr3GdLi(PO4)3F:Eu2+ was synthesized by conventional solid-state method. The surface color shows reversible white-purple changes after irradiated alternatively by UV and visible light (or thermal treat). Diffuse reflectance spectra were used to characterize the photochromic properties including coloring and bleaching. The results indicated that the optimal Eu2+ doping concentration was found to be about 0.5 mol%. Several cycles measurements including photo- and thermal-induced bleaching indicates that Sr3GdLi(PO4)3F:Eu2+ posses high fatigue resistance in photochromism performance. Based on thermoluminescence curves, the photochromism property related factors that the critical role of traps and the motion of charge carriers between traps were discussed. Finally, a schematic diagram for illustrating the photochromic mechanism was proposed.

•The photoluminescence properties of SrSnO3:Sm3+ was investigated systematically.•The long afterglow was observed in SrSnO3:Sm3+ phosphor for the first time.•The mechanism of long afterglow was discussed in detail.SrSnO3:Sm3+ persistent phosphor was successfully prepared by high temperature solid–state reaction method. The persistent phosphor was systematically studied by XRD, diffuse reflectance, photoluminescence (PL), persistent luminescence and thermoluminescence (TL) spectra. When irradiated by 254 nm ultraviolet light in advance, this phosphor shows a red-orange persistent luminescence dominated at ∼596 nm at room temperature. The dependence of Sm3+ contents on the PL and persistent luminescence properties were investigated. The TL and potential afterglow mechanism of the SrSnO3:Sm3+ phosphor was also discussed in this paper.

The Ca2Al2SiO7 samples doped with Ce3+ and Eu2+ are synthesized via a high temperature solid-state reaction. Ca2Al2SiO7: Ce3+ emits a strong UV–violet emission while Ca2Al2SiO7: Eu2+ emits a blue–green emission. The Stokes shift of the latter is greater due to a stronger crystal repulsion from ligands to Eu2+ ions. Ca2Al2SiO7: Ce3+ exhibits a stronger initial intensity and longer duration of afterglow due to the higher liberated probability of the trapped carriers. The thermoluminescence curves reveal that at least three traps exist in the phosphors. Ca2+ vacancies may enhance the electron trapping and then lead to a stronger afterglow. A possible explanation will be provided.Highlights► Long afterglow phenomenon of Eu2+ in Ca2Al2SiO7 is first reported in the present work. ► Thermoluminescence of both Ce3+ and Eu2+ in Ca2Al2SiO7 is investigated in detail. ► Crystal field theory is employed to explain the Stokes shift.

Here we report a series of multifunctional Cr3+-doped magnesium gallogermanate particles. Several minutes of ultraviolet (UV) light excitation can lead to strong near-infrared (NIR) long persistent luminescence (LPL) at 600–850 nm with a long lasting time of at least 25 h. After the disappearance of LPL, NIR photostimulated persistent luminescence (PSPL) can be rejuvenated repeatedly several times by an external photostimulus (visible or NIR light). Meanwhile, the material shows photochromic (PC) properties, i.e., the surface color can change reversibly between white/pale green and rosybrown with high fatigue resistance by alternating UV and visible light irradiation. When the temperature is increased to 300 °C, the induced rosybrown surface color can also be bleached. This new multifunctional material has potential applications in a wide range of fields, such as in vivo bio-imaging, optical information write-in and read-out media, erasable optical memory media and optical sensors. The continuous trap distribution and modulation were characterized. The optimum trap depth was determined to be 0.51–0.86 eV. In addition, we gained insight into the mechanism of multifunctional properties and the interconnection between them.

Photochromic materials have attracted increasing interest as optical switches and erasable optical memory media. Here, we report on a novel reversible colorless-cyan photochromic powder material Sr3YNa(PO4)3F:Eu2+. The photochromic properties including coloring and bleaching are characterized by reflectance spectra after the powder is irradiated by different wavelengths of light for different irradiation times or processed by thermal treatment. The results show that it can be colored by short wavelength light (200–320 nm) and bleached by longer wavelength light (320–800 nm) or thermal treatment at 240 °C. The optimal doping concentration of Eu2+ is determined to be about 0.5 mol%. It shows high fatigue resistance in photochromism performance. Electrons in 4f ground levels excited by short wavelength irradiation to higher 5d states of Eu2+ and then captured by traps are responsible for the coloring process. Correspondingly, the release of trapped electrons from two kinds of traps with different depths causes the initially fast and later slow bleaching processes. The critical role of charge carrier motions between two different traps is discussed. The colorless-cyan photochromism can be explained semi-quantitatively on the basis of obtained results. A tentative model was proposed to illustrate the PC mechanism.