•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

We report on the design of ultraviolet (UV) emitting persistent (PersL) materials. Understanding the luminescence mechanism of Bi3+ ions, the occupation rules of sites, the density functional theory (DFT) calculations and an empirical energy level scheme guided us to select the most appropriate emitters, host and traps. Finally, the NaLuGeO4:Bi3+,Eu3+ phosphor was successfully designed. The experimental results indicated that the NaLuGeO4:Bi3+,Eu3+ material is indeed able to emit excellent UV PersL, which can be recorded for more than 63 h. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Accordingly, the excitation temperature-dependent and fading thermoluminescence experiments were conducted, and the trap properties were deeply studied by the initial rising method. The results reveal the PersL mechanism and the significant role of Eu3+ codopants as foreign traps. On the basis of this work, the UV PersL of the as-designed NaLuGeO4:Bi3+,Eu3+ material is certainly promising for some potential multifunctional applications, and the design concepts of this work are indeed effective and feasible for the design of PersL materials.

•Chemical exfoliation changes the surface electricity of g-C3N4.•The partial destruction occurred during acid exfoliation.•High conjugation degree was kept in g-C3N4-PAM.•Delocalized π-system was extended in g-C3N4-PAM.•g-C3N4-PAM exhibits higher photocatalytic activity.Single layer g-C3N4 could be obtained from a protonic acid treatment of g-C3N4 or a new sandwich-like orientation growth of melamine. Through the self-assembly of melamine and polyacrylamide by hydrogen bonds and electrostatic interactions, g-C3N4, with extended planarized atomic single layer, exhibits superiority in both photocatalytic hydrogen evolution and photocatalytic degradation under visible light irradiation. Besides low efficiency, the acid exfoliation will destroy the delocalized π-system by inducing O atoms. The decrease of conjugation degree increases the optical gaps, making it hard for g-C3N4 to capture photons. On the contrary, the facile sandwich-like orientation growth of melamine highly keeps the conjugation degree of g-C3N4 and extends its delocalized π-system. Such single layer g-C3N4 is more active even better than N-doped TiO2 under visible light irradiation.Download high-res image (201KB)Download full-size imageBecause of the superiority on conjugation degree and delocalized π-system, single layer g-C3N4-PAM exhibits excellent photocatalytic activity not only on organic degradation but also on H2 evolution.

•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.

Phosphors are efficient luminescent materials that are being extensively used in lighting and displays in today's world. However, the serious emission loss at high temperatures due to thermal quenching effects is still one of the most significant challenges that limit the application of phosphors. Herein, we report a unique thermal sensitizing effect of the Na2CaGe6O14:Pr3+ phosphor, in which the red emission of Pr3+ is significantly enhanced with the increase in temperature, even upto 250 °C. Moreover, the emission of the phosphor still keeps increasing over time at high temperatures. This thermally induced emission increase originates from the generation of more defect levels and more efficient energy transfer from the defects to Pr3+ at higher temperatures. This significant discovery may enlighten a new strategy to minimize or even completely eliminate the serious thermally induced emission loss of the phosphors.

A new concept of a “Persistent Photocatalysis (PersP)” effect is defined for the first time according to the observation that the black peony-like BiOCl material is able to efficiently degrade Rhodamine B dye after removing visible light irradiation, just as in persistent luminescence of phosphors. The discovery of the PersP effect provides a potential solution to realize full-time photocatalytic applications. The PersP effect was justified through a series of decomposition experiments, and its potential prospect for full-time application was evaluated by experiments as well. On the basis of the results, a possible PersP mechanism of the black peony-like BiOCl material has been proposed.

An excellent persistent luminescence (PersL) phosphor NaCa2GeO4F:Mn2+,Yb3+ has been synthesized by traditional solid-state reaction. By controlling the occupation sites of Mn2+ emitters, the PersL color of this phosphor can be optionally tuned in the red to green-yellow region, and the maximum spectral shift is more than 50 nm. Significantly, the red PersL can be measured for approximately 13 and 3 h (0.32 mcd/m2) and can be observed for more than 20 and 5 h with dark-adapted vision after exposure to ultraviolet irradiation and artificial sunlight, respectively. The crystal/electronic structure and photoluminescence/PersL properties of this phosphor have been investigated in detail. A series of the excitation temperature-dependent thermoluminescence experiments and the initial rising method have been conducted to study the trap properties of this phosphor. It reveals the reasons for the variation of PersL color, excellent red PersL, and degradation of green-yellow PersL. According to the results, the as-prepared NaCa2GeO4F:Mn2+,Yb3+ can be considered as an excellent red PersL phosphor, and it also has potential for application in optical storage.

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.

A novel phosphor of un-doped SrZrSi2O7 material with blue long lasting phosphorescence which could be recorded for about 5400 s (0.32 mcd/m2) was developed. It revealed that both the emission centers and traps levels were related to the oxygen-deficient defects which were induced in reducing atmosphere. The filling and fading experiments indicated that the traps levels in SrZrSi2O7 were continuous in distribution. The influence of shallow traps on deep traps was investigated and the important role of the bridge effect was revealed. The un-doped SrZrSi2O7 material obtained in reducing atmosphere showed potential application as a cheap blue long lasting phosphorescence phosphor.LLP mechanism of the un-doped SrZrSi2O7 material synthesized in reducing atmosphere

•The blue long lasting phosphorescence of Sr5(PO4)3Cl:Eu2+ is first reported.•Filling and fading experiments are carried out for revealing natures of traps.•The afterglow mechanism for independent traps of Sr5(PO4)3Cl:Eu2+ is proposed.A novel blue emitting long lasting phosphorescence phosphor Sr5(PO4)3Cl:Eu2+ is synthesized by solid state method at 1223 K in reducing atmosphere. The afterglow emission spectrum shows one broad band centered at 441 nm due to the 5d–4f transition of Eu2+ at six coordinated Sr(II) sites and the color coordinates are calculated to be (0.149, 0.095) which is close to the light blue region. The excitation band is in 240–430 nm and partly overlaps the solar irradiation on Earth's surface. The long lasting phosphorescence of the optimal sample doping by 0.1 mol%Eu2+ can be recorded for about 1040 s (0.32 mcd/m2). Thermoluminescence shows that there are at least three types of traps corresponding to peaks at 340 K, 382 K, 500 K, respectively. The filling and fading experiments reveal that the traps in Sr5(PO4)3Cl:Eu2+ are independent. The shallow traps (340 K) essentially contribute to the visible long lasting phosphorescence, while the deep traps (382 K and 500 K) are proved to be very stable. Thus, the Sr5(PO4)3Cl:Eu2+ material shows potential applications as not only a long lasting phosphorescence phosphor, but also an optical storage material.

•Violet-blue afterglow luminescence is first observed in non-doped SrZrO3.•Afterglow of SrZrO3 partly overlaps absorption of commercial photocatalyst TiO2.•SrZrO3 may be applied to keep photocatalytic activity of TiO2 at night.Non-doped SrZrO3 material is synthesized by solid state reaction at 1300 °C in air. The violet-blue afterglow luminescence of SrZrO3 centered at 395 nm is firstly observed. The afterglow emission band (300–550 nm) of SrZrO3 partly overlaps the absorption (200–400 nm) of commercial photocatalyst TiO2 (P25). Thus, the SrZrO3 shows potential application to support photocatalytic activity of TiO2 even at night. The decay curve indicates that the afterglow luminescence of the present SrZrO3 can last less than 100 s (0.32 mcd/m2) and thus the present SrZrO3 still needs further improvement for practical application. The thermoluminescence indicates that at least two types of deep traps exist in the SrZrO3 and the depths of traps are roughly calculated to be as deep as 0.98 eV and 1.76 eV. It reveals that the short afterglow time of the SrZrO3 is not due to the lack of enough traps but the traps in SrZrO3 being too deep. Therefore, decreasing the depth of traps in SrZrO3 is our following emergency work.

•Self-activated green afterglow is first observed in non-doped Ca2ZrSi4O12.•Thermoluminescence related to traps in Ca2ZrSi4O12 are studied and calculated.•Contributions of the traps with different depths on afterglow are revealed.•Afterglow luminescence of rare earth doped Ca2ZrSi4O12 is also investigated.Un-doped Ca2ZrSi4O12 material is prepared using a solid state reaction and it emits intense green afterglow luminescence peaking at 490 nm. The afterglow luminescence can be recorded for about 4800 s (0.32 mcd m−2). The thermoluminescence revealed that at least four types of traps existed in the Ca2ZrSi4O12 material and the depths of these traps were calculated. The contributions of these traps on the afterglow luminescence were also investigated in detail. Accordingly, a possible afterglow mechanism of Ca2ZrSi4O12 was proposed. Moreover, Ca2ZrSi4O12 was also doped by rare earth or metal ions for developmental purpose and we arrived at some useful conclusions according to the experimental results.

In order to interpret the origin of two emission quenching concentrations and a sharp increase of afterglow at certain Sm3+ doping concentration in Ba2SnO4:Sm3+ phosphor, the Eu3+ is used as a probe and it reveals that the Sm3+ ions occupy Sn4+ sites at low Sm3+ concentration and then the Ba2+ sites at a high concentration. The Sm3+ centers at different sites lead to two quenching processes and the two quenching concentrations effect. The thermoluminescence reveals that the substitution of Sm3+ for Ba2+ sites will induce a large amount of shallow hole traps and it should be mainly responsible for the sharp enhancement of the afterglow.Highlights► We observe the effect of two quenching concentrations in Ba2SnO4:Sm3+. ► Ba2SnO4:Sm3+ shows a sharp increase of afterglow time at certain Sm3+ content. ► Both the effects are related to the occupancy sequence of two sites for doping Sm3+. ► We present a feasible interpretation for our observations.

The Mg2SnO4:Eu3+ phosphor with reddish photoluminescence, green afterglow and photostimulated luminescence is obtained by the solid state method. The host related afterglow is greatly enhanced by doping of Eu3+ and it can last nearly 6 h when the Eu3+ concentration is 1 mol%. The photostimulated luminescence is found to be weakened by doping of Eu3+. It was revealed that all the shallow traps and a part of the deep traps are involved in afterglow. The majority of deep traps are responsible for photostimulated luminescence. The impact of doping Eu3+ on the afterglow and photostimulated luminescence is investigated and we propose a feasible interpretation.Highlights► Novel Mg2SnO4:Eu3+ with red PL, green AG and PSL is obtained. ► Doping of Eu3+ increases the host related AG and decreases PSL. ► Effect of doping Eu3+ on luminescence of Mg2SnO4 is clarified. ► Oxygen vacancies are revealed to be the key factors.

The ultraviolet irradiation degradation of lamps using BaMgAl10O17:Eu2+,Mn2+ phosphor is investigated. The X-ray photoelectron spectra demonstrate that the oxidation of Eu2+ is taking place during ultraviolet irradiation in air. The experiment in nitrogen indicates that the oxidation of Eu2+ is directly related to the oxygen in air and should be mainly responsible for the degradation of Eu2+. It reveals that the Mn2+ centers always remain stable during irradiation but its emission is involved in the energy transfer of Eu2+→Mn2+. Thus, the oxidation of Eu2+ also leads to the degradation of Mn2+.Highlights► Ultraviolet irradiation damage of lamp using BaMgAl10O17:Eu2+,Mn2+ is studied. ► Oxidation of Eu2+ is the main reason for the ultraviolet irradiation damage. ► Oxygen in air is the crucial factor for oxidation of Eu2+ by irradiation. ► Mn2+ centers always keep stable during the ultraviolet irradiation. ► Degradation of Mn2+ is involved in the energy transfer of Eu2+→Mn2+.

The novel SnO2:Sm3+,Zr4+ afterglow phosphor is synthesized by solid state reaction. The SnO2:Sm3+ doesn’t show afterglow. But, after co-doping Zr4+ in SnO2:Sm3+, the red afterglow luminescence of Sm3+ is firstly observed and the important role of Zr4+ on the afterglow is investigated. The photoluminescence shows that the doping of Zr4+ increases the emission lines of Sm3+ and decreases the emission band due to trapped hole center. The thermoluminescence reveals that the co-doping of Zr4+ induces the increase of shallow traps corresponding to the thermoluminescence peak at 48 °C. The depth of the traps is calculated to be 0.61 eV. The positron annihilation indicates that the traps are due to negatively charged tin vacancies and they play the important role on the afterglow of Sm3+ as hole traps.Highlights► A novel red afterglow phosphor SnO2:Sm3+,Zr4+ is obtained. ► The important role of Zr4+ on the afterglow is revealed. ► The defects in SnO2 are first studied by positron annihilation.

Ca2GeO4:Eu3+ phosphors were synthesized by the solid state method. The ultraviolet and vacuum ultraviolet excited photoluminescence properties were investigated in detail. It revealed that the emission of Ca2GeO4:Eu3+ comprised two parts: the red emission of Eu3+ and host defect emission in 330–550 nm. Ca2GeO4:Eu3+ presented intense excitation intensity at 163–200 and 466 nm, which suggested the potential applications in plasma display panels and light emitting diodes. The excitation spectra were studied to identify the photoluminescence mechanisms of Ca2GeO4:Eu3+. First principles calculation within the local density approximation of the density functional theory was applied to calculate the electronic structure and linear optical properties of Ca2GeO4.Research highlights► Emission of Ca2GeO4:Eu3+ comprised of emissions of Eu3+ and host emission. ► Ca2GeO4:Eu3+ exhibited different colors such as red, pink, blue and purple. ► Excitation intensity of Ca2GeO4:Eu3+ at 466 nm was 1.7 times of that at 301 nm. ► Ca2GeO4:Eu3+ is a potential candidate applied in LEDs, PDPs or free-Hg lamps.

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.

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.

We report on the design of ultraviolet (UV) emitting persistent (PersL) materials. Understanding the luminescence mechanism of Bi3+ ions, the occupation rules of sites, the density functional theory (DFT) calculations and an empirical energy level scheme guided us to select the most appropriate emitters, host and traps. Finally, the NaLuGeO4:Bi3+,Eu3+ phosphor was successfully designed. The experimental results indicated that the NaLuGeO4:Bi3+,Eu3+ material is indeed able to emit excellent UV PersL, which can be recorded for more than 63 h. This exciting result is sufficiently encouraging for the initiation of a more thorough investigation. Accordingly, the excitation temperature-dependent and fading thermoluminescence experiments were conducted, and the trap properties were deeply studied by the initial rising method. The results reveal the PersL mechanism and the significant role of Eu3+ codopants as foreign traps. On the basis of this work, the UV PersL of the as-designed NaLuGeO4:Bi3+,Eu3+ material is certainly promising for some potential multifunctional applications, and the design concepts of this work are indeed effective and feasible for the design of PersL materials.