Eu3+ doped Mg2Al4Si5O18 phosphors were prepared by the solid-state reaction. The first principles calculation, XRD, diffuse reflection spectra, photoluminescence spectra and thermal quenching are carried out to investigate the electron structure, crystal structure, photoluminescence and thermal properties. The calculation results show that Mg2Al4Si5O18 possesses the direct band gap of about 5.1 eV. With the introduction of Eu3+, the energy gap becomes obviously smaller due to the discontinuity of exchange-correlation energy. Between HOMOs and LOMOs, a series of f orbitals of Eu3+ can be observed, which is the essential condition to realize the efficient 4f–4f transitions of Eu3+. The experimental results indicate that the samples can efficiently absorb the UV-light and emit the red light with the highest peak at 614 nm. With the co-doping of Bi3+ as sensitizer, the emission intensity of Eu3+ increases by about 49% due to the energy transfer between Bi3+ and Eu3+. With the introduction of Li+/Na+/K+ as charge compensators, the emission intensities of Mg2Al4Si5O18: Eu3+ are enhanced by about 22%, 18% and 5%. With the temperature increase, the emission intensity of all samples, especially the Bi3+ doped samples, dramatically declines, which reveals two important effects: one is that the Eu3+ emission is very sensitive to temperature, and other is that the complex energy transfer process among the excited and ground states of Eu3+, Bi3+ or host absorption occurs. To explain the degradation, the mechanism based on the configurational coordinate diagram is proposed and this model could be helpful for the understanding of the energy transfer mechanism among the various energy levels in the process of temperature change.

•Sufficient long persistent luminescence was firstly induced in amorphous SiO2.•Nano-sphere SiO2 was calcinated with carbon to induce persistent luminescence.•Blue Persistent luminescence of optimal sample can last for 1 h (0.32 mcd/m2).Intense blue persistent luminescence (PersL) with sufficiently long duration time was firstly observed in SiO2 particles after calcination with carbon. In indicates that the intense PersL of the optimal SiO2 sample calcinated with carbon (1:2) at 600 °C can be recorded for about 1 h (0.32 mcd/m2) and is actually visible for even more than 3 h by the dark-adapted vision in darkness. It reveals that the defects formatted during the calcination with carbon should be associated with oxygen vacancies and they play very important roles as emitters and traps, contributing to the PersL. The depth of the dominant traps in the optimal SiO2 sample is calculated to be about 0.71 eV, which is in a suitable range for PersL (0.5–0.8 eV).Figure optionsDownload full-size imageDownload high-quality image (146 K)Download as PowerPoint slide

•LiGaSiO4:Mn2+ shows green PersL for 2.1–6 h after UV or sunlight irradiation.•Crystal and electronic structure of LiGaSiO4 and Mn2+ sites are investigated.•Trap distribution and roles of traps are studied dependent on TL experiments.A novel orthosilicate persistent phosphor LiGaSiO4:Mn2+ has been developed by solid state reaction method. The refined crystal structure of the LiGaSiO4 is solved. The photoluminescence and persistent spectra, decay curve and thermoluminescence have been investigated in details. It reveals that the Mn2+ at Li+ sites in the LiO4 tetrahedron are able to show intense green persistent luminescence, which can be measured for approximately 6 h and 2.1 h (0.32 mcd/m2) after exposure to ultraviolet and artificial sunlight irradiation. The trap distribution of phosphor is studied by using a series of excitation temperature dependent thermoluminescence experiments based on initial rising method. The different roles of the shallow and deep traps on the persistent luminescence have been revealed by the thermoluminescence fading experiments.

We combine nonequivalent substitution and charge-induced emitter-migration approaches and design an efficient method to optionally tune the spectral and duration properties of NaCa2GeO4F:Mn2+ phosphor. A series of representative codopants have been investigated in detail and classified into two categories: RA (RA = Li+, Al3+, N3–, Ga3+, B3+) and RB (RB = Mg2+, F–, Bi3+, Zn2+, Cd2+, Sc3+, Tm3+). Results reveal that the nonequivalent substitution of RA codopants would induce foreign negative defects and stabilize Mn2+ emitters at octahedral Na/Ca sites for red emission. In constrast, the RB codopants would generate foreign positive defects and make Mn2+ emitters migrate to tetrahedral Ge4+ sites for green-yellow emission. At the same time, the RA codopants are in favor of the generation of intrinsic positive traps with shallow trap depth and thus efficiently improve the duration properties of phosphors. On the basis of the experimental results, a possible nonequivalent substitution and charge-induced emitter-migration model has been proposed, and we can optionally tune the spectral (568 ↔ 627 nm) and the duration (minutes to more than 6 h) properties according to this model.

An energy level scheme of the NaCa2GaGe5O14:Ln3+/Ln2+ phosphors has been constructed by collecting spectroscopy data. The energy level positions of Ln2+/Ln3+ can be used to gain insight into the photoluminescence and long persistent luminescence properties of the NaCa2GaGe5O14:Ln3+/Ln2+ phosphors and the ability of Ln3+ codopants as foreign electron traps. All the theoretical predictions have been confirmed by the experimental results. For this case, this energy level scheme is reliable and can be used as a transferable empirical tool to study the luminescent properties of known phosphors, and even guide the further development of new phosphors.

•A color-tunable phosphor is firstly synthesized by the solid state reaction.•The energy transfer mechanism between Ce3+ and Tb3+ is carefully studied.•The phosphor shows an interesting temperature-dependent luminescence behavior.•By configurational coordinate diagram, thermal regression mechanism is explained.A series of phosphosilicate phosphors Sr8La2(PO4)3.5(SiO4)2(BO4)0.5BO2: Ce3+, Tb3+ are synthesized by solid-state reaction for the first time. The XRD Rietveld refinement presents that the compound crystallizes in a trigonal crystal system with space group P3¯ (No. 147). Under the excitation of 340 nm, commonly blue and yellowish green emissions from Ce3+ and Tb3+ are detected and can generate the color-tunable light with chromaticity coordinates from (0.188, 0.095) to (0.351, 0.517) by changing the ratio of Ce3+/Tb3+. By the photoluminescence spectra, decay times and energy transfer efficiency, the mechanism of energy transfer between Ce3+ and Tb3+ has been carefully investigated. With the increase of temperature, the Ce3+ or Tb3+ single doped sample shows an excellent thermal property, but when the Ce3+ and Tb3+ are co-doped into the host, the thermal property of sample seriously degenerates. This result indicates that the change of temperature can affect the energy transfer between Ce3+ and Tb3+ strongly and based on the configurational coordinate diagram, this phenomenon is explained reasonably.

We successfully tailor the properties of a well-known commercial lamp with the Zn2SiO4:Mn2+ phosphor as a novel, highly efficient, long-lasting green phosphor by using the co-doping method. The long-lasting phosphorescence (LLP) of the optimal Zn2SiO4:Mn2+,Yb3+ sample can be recorded for approximately 30 h (0.32 mcd m−2) and is visible for even more than 60 h in the dark by using dark-adapted vision. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Several classical methods of investigation including decay curves, thermoluminescence, fading experiments, multi-peak fitting based on general-order kinetics, and first-principles calculations are used in this study to examine the LLP properties, the effects of such co-dopants and the nature of traps in detail. The important retrapping and tunneling effects, combined with a kinetics investigation, are discussed. A modified law concerning the influences of co-dopants on the traps around the Mn2+(3d5, d → d type) centers and the LLP properties are summarized. Finally, the LLP mechanism of the Zn2SiO4:Mn2+,Yb3+ phosphor is proposed.

A single-phase white-light emitting phosphor MgY4Si3O13:Dy3+ was synthesized using the solid state method under reducing atmosphere and in air for the first time. Upon ultraviolet light excitation, the phosphor exhibits intense warm white light emission with optimal CIE chromaticity coordinates of 0.432 and 0.421 and a correlated color temperature value of 3160 K. The emission intensities of samples synthesized under the reducing atmosphere are superior to those in air due to the sensitization of host to Dy3+. With the increase in temperature, MgY4Si3O13:Dy3+ presents satisfactory thermal properties and based on the configurational coordinate diagram, the energy transfer mechanism between the host and Dy3+ is carefully investigated. All the results indicate that MgY4Si3O13:Dy3+ could be a promising phosphor for warm white UV-LEDs.

•The influence of the doping of Ca2+ on the PL spectra was carefully investigated.•The trace doping of Al3+ and P5+ with Y3+ and K+ can enhance the PL intensities.•Thermal quenching phenomenon was explained by configurational coordinate diagram.The yellow–orange phosphors Sr1.99−x−yCaxMySi1−yZyO4: 0.01Eu2+ (M = Y3+, K+, Z = Al3+, P5+, 0 ⩽ x ⩽ 0.9, 0 ⩽ y ⩽ 0.01) were synthesized by the solid state reaction. X-ray diffraction and photoluminescence spectra were utilized to characterize the samples. The results indicate that the phosphors can be efficiently excited by the UV–blue light and show a broad band emission from about 425 to 700 nm. Ca2+ plays an important role in the red-shift of the emission band in Sr1.99−xCaxSiO4: 0.01Eu2+. When the Ca2+ concentration x = 0.7, the emission peak under the excitation of 450 nm reaches a maximum at about 600 nm, which implies that the samples Sr1.99−xCaxSiO4: 0.01Eu2+ could serve as a red phosphor for the blue LEDs. The trace doping of Al3+ and P5+ with Y3+ and K+ as charge compensation significantly enhances the emission intensities of Sr1.29Ca0.7SiO4: 0.01Eu2+. In addition, thermal properties of typical samples are also carefully investigated.A simple solid-state route was adopted to synthesize a series of phosphors Sr1.99−x−yCaxMy(Si1−yZy)O4: 0.01Eu2+. The PL spectra indicate that Ca2+ plays a significant role in enhancing red-emitting component. The trace doping of Al3+ and P5+ with Y3+ and K+ as charge compensation obviously enhances the emission intensities of Sr1.29Ca0.7SiO4: 0.01Eu2+. Based on the configurational coordinate diagram, the thermal quenching phenomenon of typical samples is also reasonably explained.

A single phase emission-tunable Ce3+,Mn2+ co-doped phosphosilicate Sr7La3[(PO4)2.5(SiO4)3(BO4)0.5](BO2) phosphor was synthesized by a solid-state reaction. Commonly blue and orange broad band emissions from Ce3+ and Mn2+ are detected under excitation at 351 nm. Combined with the crystallographic data from Rietveld refinements, the blue and orange bands can be fitted by the Gaussian function in accordance with the three different sites. By adjusting the ratio of Ce3+/Mn2+, warm-white light is generated with a correlated color temperature of 2500–4500 K. The mechanism of energy transfer between Ce3+ and Mn2+ has also been carefully investigated by the photoluminescence spectra and decay times. The thermal properties from 20 to 250 °C present an abnormal changing trend. With the increase in temperature, the Ce3+ or Mn2+ single-doped samples show excellent thermal properties, while for the Ce3+ and Mn2+ co-doped sample, the thermal properties are severely degenerated. Based on a configurational coordinate diagram, an underlying mechanism for thermal quenching is proposed which can reasonably explain the phenomenon. What is more, the mechanism could be helpful for understanding the thermal properties of phosphors co-doped with multiple activators as a reference.

A series of Mg2−xAl4Si5O18:xDy3+ (0 ≤ x ≤ 0.18) samples were synthesized, for the first time, by a solid state method both in a reducing atmosphere and in air. XRD, diffuse reflectance spectra, excitation spectra, emission spectra, decay times and thermal quenching were used to investigate the structure, photoluminescence, energy transfer and thermal properties. The results show that Mg2Al4Si5O18:Dy3+ can efficiently absorb UV light and emit violet-blue light in the range of 400 to 500 nm from oxygen vacancies in the host as well as blue light (∼480 nm) and yellow light (∼576 nm) from the f–f transitions of Dy3+. The emission intensities of the samples obtained under a reducing atmosphere are far superior to those of the samples obtained in air due to an efficient energy transition from oxygen vacancies in the host to Dy3+. An analysis of the thermal quenching shows that the phosphor Mg2Al4Si5O18:Dy3+ has excellent thermal properties. The emission intensities of typical samples synthesized in a reducing atmosphere and in air at 250 °C are 70% and 81% of their initial intensities at 20 °C, respectively. In addition, the emission colors of all of the samples are located in the white light region and the optimal chromaticity coordinates and Correlated Color Temperature are (x = 0.34, y = 0.33) and 5129 K, respectively. Therefore, these white Mg2Al4Si5O18:Dy3+ phosphors could serve as promising candidates for white-light UV-LEDs.

Europium-doped apatite Ca10(SiO4)3(SO4)3F2 (CSSF) has been successfully synthesized by solid state reaction. The crystal structure of CSSF:0.006Eu2+ is refined by the Maud refinement method. Optical properties of the prepared samples are found to depend on the rare-earth metal–oxygen distances and lattice iconicity. The excitation spectra of the CSSF:Eu2+ phosphors centered at 350 nm and covered the range from 250 to 450 nm. Under 350 nm excitation, the emission spectra of CSSF:Eu2+ phosphors show a blue (centered at 420 nm) and a green (centered at 525 nm) emission band, respectively. Meanwhile, the concentration quenching and energy transfer mechanism have been investigated via the configuration coordinate diagram. The key parameters, such as the temperature-dependent photoluminescence and CIE values of the CSSF:Eu2+ phosphor have also been studied.

•A new Ca2La8(GeO4)6O2 (CLGO) compound has been synthesized for the first time.•The crystal structure of CLGO has been refined by Maud refinement method.•Photoluminescence spectra of CLGO:RE3+ were firstly investigated.A new Ca2La8(GeO4)6O2 (CLGO) compound has been synthesized via solid-state reaction process for the first time. The crystal structure of CLGO was refined and determined by Maud Program. The photoluminescence spectra (PL), cathodoluminescence spectra (CL), and lifetimes as well as temperature dependence of photoluminescence of CLGO:RE3+ (RE3+=Eu3+, Tb3+, Dy3+, Sm3+, Tm3+) were investigated in detail. Under the excitation of ultraviolet, CLGO:RE3+ (RE3+=Eu3+, Tb3+, Dy3+, Sm3+, Tm3+) show red, green, yellow, orange, violet emission, respectively.

A warm-white emitting persistent luminescence phosphor Lu3Al2Ga3O12:Pr3+ was synthesized by solid state method at 1600 °C in air. The refined crystal structure of Lu3Al2Ga3O12 host was solved by X-ray diffraction (XRD). The photoluminescence spectra, decay curve and thermoluminescence were investigated. It was revealed that the persistent luminescence originated from the f-f transitions of Pr3+ emitters at Lu3+ sites in LuO8 polyhedrons, and it showed white color due to the 3P0→3H4, 3P1→3H5, 3P0→3H5, 3P0→3H6, 3P0→3F2, 3P0→3F3 and 3P0→3F4 transitions of Pr3+ emitters in a wide range. The persistent luminescence of Pr3+ in this host could be promoted by f-d transition (278 nm) but f-f transitions, due to the different thermal activation energy. The persistent luminescence of the optimal sample could be actually recorded for 3 h by the definition of 0.32 mcd/m2 and was visible for more than 7 h by dark-adapted vision in darkness. The initial depth of the dominant shallow traps was calculated to be about 0.56 eV, which is suitable for persistent luminescence. The different roles of the shallow and deep traps on the persistent decay process were investigated. Accordingly, the persistent luminescence processes and mechanism of the as-synthesized Lu3Al2Ga3O12:Pr3+ phosphors were proposed.

A single phase emission-tunable Ce3+,Mn2+ co-doped phosphosilicate Sr7La3[(PO4)2.5(SiO4)3(BO4)0.5](BO2) phosphor was synthesized by a solid-state reaction. Commonly blue and orange broad band emissions from Ce3+ and Mn2+ are detected under excitation at 351 nm. Combined with the crystallographic data from Rietveld refinements, the blue and orange bands can be fitted by the Gaussian function in accordance with the three different sites. By adjusting the ratio of Ce3+/Mn2+, warm-white light is generated with a correlated color temperature of 2500–4500 K. The mechanism of energy transfer between Ce3+ and Mn2+ has also been carefully investigated by the photoluminescence spectra and decay times. The thermal properties from 20 to 250 °C present an abnormal changing trend. With the increase in temperature, the Ce3+ or Mn2+ single-doped samples show excellent thermal properties, while for the Ce3+ and Mn2+ co-doped sample, the thermal properties are severely degenerated. Based on a configurational coordinate diagram, an underlying mechanism for thermal quenching is proposed which can reasonably explain the phenomenon. What is more, the mechanism could be helpful for understanding the thermal properties of phosphors co-doped with multiple activators as a reference.

We successfully tailor the properties of a well-known commercial lamp with the Zn2SiO4:Mn2+ phosphor as a novel, highly efficient, long-lasting green phosphor by using the co-doping method. The long-lasting phosphorescence (LLP) of the optimal Zn2SiO4:Mn2+,Yb3+ sample can be recorded for approximately 30 h (0.32 mcd m−2) and is visible for even more than 60 h in the dark by using dark-adapted vision. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Several classical methods of investigation including decay curves, thermoluminescence, fading experiments, multi-peak fitting based on general-order kinetics, and first-principles calculations are used in this study to examine the LLP properties, the effects of such co-dopants and the nature of traps in detail. The important retrapping and tunneling effects, combined with a kinetics investigation, are discussed. A modified law concerning the influences of co-dopants on the traps around the Mn2+(3d5, d → d type) centers and the LLP properties are summarized. Finally, the LLP mechanism of the Zn2SiO4:Mn2+,Yb3+ phosphor is proposed.