Duration Of Persistent Luminescence Research Articles

Persistent ultraviolet luminescence and photocatalytic properties of SiO2-Zn2SiO4:Ga,Pb nanoparticles

Persistent phosphors possess unique afterglow optical properties. In this paper, a class of ultra-violet (UV) persistent luminescence nanoparticles were developed for catalytic photodegradation applications. UV persistent luminescence nanoparticles of SiO2-Zn2SiO4:Ga and SiO2-Zn2SiO4:Ga,Pb were successfully synthesized by using a mesoporous template method. The UV persistent luminescence intensity of SiO2-Zn2SiO4:Ga at 405 nm was enhanced up to ca. 3.5 times by co-doping with Pb2+ (396 nm), along with longer persistent luminescence duration. The photodegradation results indicate that it is useful to introduce UV persistent luminescence property into SiO2-Zn2SiO4:Ga,Pb to obtain enhanced catalytic activity of SiO2-Zn2SiO4 with a bigger catalytic oxidation reaction kinetic constant (up to ∼4 times). This kind of UV persistent catalysis strategy may become a potential feasible method for better catalytic photodegradation activity. The UV persistent photocatalyst has potential applications in the photooxidation of organic molecules in high chroma and/or turbidity aqueous systems.

Continuous tuning of persistent luminescence wavelength by intermediate-phase engineering in inorganic crystals

Multicolor tuning of persistent luminescence has been extensively studied by deliberately integrating various luminescent units, known as activators or chromophores, into certain host compounds. However, it remains a formidable challenge to fine-tune the persistent luminescence spectra either in organic materials, such as small molecules, polymers, metal-organic complexes and carbon dots, or in doped inorganic crystals. Herein, we present a strategy to delicately control the persistent luminescence wavelength by engineering sub-bandgap donor-acceptor states in a series of single-phase Ca(Sr)ZnOS crystals. The persistent luminescence emission peak can be quasi-linearly tuned across a broad wavelength range (500–630 nm) as a function of Sr/Ca ratio, achieving a precision down to ~5 nm. Theoretical calculations reveal that the persistent luminescence wavelength fine-tuning stems from constantly lowered donor levels accompanying the modified band structure by Sr alloying. Besides, our experimental results show that these crystals exhibit a high initial luminance of 5.36 cd m−2 at 5 sec after charging and a maximum persistent luminescence duration of 6 h. The superior, color-tunable persistent luminescence enables a rapid, programable patterning technique for high-throughput optical encryption.

Two viologen-based complexes as persistent luminescent materials and their applications in inkless print and anticounterfeiting

Viologen-based complexes have garnered significant attention due to their multifunctional stimuli-responsive properties and tunable persistent luminescence. However, achieving ultralong afterglow emission and color change in these complexes remains a challenge, limiting their application in the field of persistent luminescence. Herein, two novel viologen-based complexes were successfully designed and synthesized using N,N′-bis(2-carboxyethyl)-4,4′-bipyridinium dichloride (H2bybpy) ligands and trimesic acid (H3BTC) with the transition metals Zn(II)/Cd(II). Complexes 1 and 2 display reversible photochromic and electrochromic properties. Interestingly, complexes 1 and 2 in their crystal state exhibit dual fluorescence and persistent luminescence, emitting a green and cyan afterglow when the UV lamp is turned off at 77 K. Incorporating phosphorescent molecules and changing the metal significantly extended the duration of persistent luminescence and altered the hue. The complexes were also demonstrated to have potential applications in inkless printing, color-changing films, data encryption, and anti-counterfeiting. This work enhances the application of viologen-based complexes in light-controlled persistent fluorescence and provides ideas for achieving ultra-long afterglow emission.

Optimization of persistent luminescence performance of zinc gallogermanates

X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, and X-ray photoelectron spectroscopy, combined with instrumental analysis, have been employed to identify and characterize the physical differences between Zn3Ga2GeO8 (ZGGO-s, s as in stoichiometric) and Zn3Ga2Ge2O10 (ZGGO-e, e as in excess) solid solutions. The two materials differ in the addition of GeO2 (in the case of the ZGGO-e sample) to the solid solution of ZnGa2O4 and Zn2GeO4. The optimum sintering temperature for these materials is 1000 °C. The photoluminescence spectra comprise a broad feature between 400 and 600 nm which is slightly red-shifted in the case of ZGGO-e. Notably, ZGGO-e exhibits superior performance for both the intensity and duration of persistent luminescence at room temperature, with emission maximum at 515–517 nm. The performance of the chromium-doped sample, with persistent luminescence emission at 697 nm, is also superior for ZGGO-e. The reasons behind such a significant enhancement of persistent luminescence performance for ZGGO-e sample were investigated in this paper. We have found out that long persistent luminescence in both samples is governed by trap depth distributions. In the case of ZGGO-e, the addition of GeO2 promotes the formation of deeper traps changing the shape of the resulting trap distribution and hence improving the room temperature persistent luminescence of this compound.

First-principles study on persistent luminescence mechanism of LiYGeO4:Eu3+

LiYGeO4:Eu3+ is a red persistent luminescent material with a duration of more than 21 h. Although its persistent luminescence phenomenon has been fully studied, its detailed mechanism is still the subject of debates. Herein, we performed first-principles study on the intrinsic point defects and the charge transfer processes in LiYGeO4:Eu3+ to reveal the mechanism of persistent luminescence. The results show that, under charge transfer excitation, the electron is promoted from the valence band (oxygen ion ligand) to the central Eu3+ ion to form Eu2+ ion in LiYGeO4:Eu3+, leaving a hole behind. The charge transfer excitation can relax quickly to the excited state of the Eu3+ ion, which produces the characteristic 5D0 → 7FJ (J = 0–6) emission. The Li vacancies (VLi) and the antisite defects of Li replacing Y site (LiY) and Y replacing Li site (YLi) are main defects, while O vacancies (VO) are less important in concentration due to high formation energy. VLi and LiY can serve as hole-type traps, with the trap depths suitable for trapping the holes produced by illumination. The delayed release holes can combine with the Eu2+ left behind by the illumination, leading to persistent luminescence. The VLi trap is shallower than LiY, and the latter is responsible for the long duration of persistent luminescence. A schematic based on the calculation results is constructed to illustrate the mechanism of persistent luminescence.

A novel near-infrared phosphor Mg2InSbO6:Cr3+ with high quantum efficiency and considerable persistent luminescence duration

A novel near-infrared phosphor Mg2InSbO6:Cr3+ with high quantum efficiency and considerable persistent luminescence duration is successfully prepared.

Enhanced persistent luminescence via Si4+ co-doping in Y3Al2Ga3O12:Ce3+, Yb3+, B3+

Persistent luminescence phosphors with long duration and high emitting intensity have attracted considerable attention for applications in safety signage and energy storage. Herein, we successfully introduce non-equivalent ions Si4+ into Al3+ sites in the garnet phosphor Y3Al2Ga3O12:Ce3+,Yb3+,B3+ by conventional solid-state reaction. The persistent luminescence duration has been dramatically enhanced over 40 h at the 0.32 mcd/m2 threshold value after visible light radiation, almost twice longer than the sample without Si4+. Moreover, the afterglow emission intensity of the persistent luminescence is also improved. We confirm that the synthesized phosphors possess not only deeper trap depth but also wider trap distribution and higher trap density after the cooperation of Si4+. The initial rise approach is used by performing a series of thermoluminescence analyses at various temperatures after 432 nm excitation, which demonstrates the exact trap distribution from 0.47 to 1.11 eV. At the end, the mechanism of the persistent luminescence is depicted using a schematic energy diagram of the vacuum referred binding energy of Y3Al2Ga3O12.

Pressure-induced variation of persistent luminescence characteristics in Y3Al5-xGaxO12:Ce3+-M3+ (M = Yb, and Cr) phosphors: opposite trend of trap depth for 4f and 3d metal ions.

Changing the electronic structure of materials by pressure and the accompanying changes in optical properties have attracted scientific interest. We have reported that the energy position of the conduction band (CB) bottom and the crystal field splitting of the Ce3+:5d excited level in Y3Al5-xGaxO12:Ce3+ are changed by applying pressure, which results in the red shifting of the Ce3+:5d → 4f luminescence and the increase of the quenching temperature. We also reported dramatic improvement of the persistent luminescence performance by either Cr3+ or Yb3+ codoping into the Y3Al5-xGaxO12:Ce3+ phosphors. The different trap depths formed by Cr3+ and Yb3+ affect the initial persistent luminescence intensity and the persistent luminescence duration. In this study, the effect of pressure on the persistent luminescence performance was investigated. For the Y3AlGa4O12:Ce3+-Yb3+ phosphor, the slope of persistent luminescence decay curve becomes more gentle with increasing pressure, while for the Y3AlGa4O12:Ce3+-Cr3+ phosphor the slope becomes steeper. These results indicate that the trap depth of Yb3+ becomes deeper and that of Cr3+ becomes shallower with increasing pressure. Based on the pressure-dependence of the luminescence quenching and the trap depth change estimated from the decay slopes, the relative electronic energies of the CB bottom and the Yb2+ (4f14) or Cr2+ (3d4) levels are discussed. The CB bottom energy is increased relative to the ground 1S0 state of Yb2+ with increasing pressure, which results in deepening of the electron trap depth of the Yb2+ state. The opposite tendency of the Cr3+ codoped sample was described by a decreasing tendency of the energy gap between the CB bottom and the Cr2+:eg level, the relative energy level of which is increased by the increase of the crystal field with increasing pressure in the garnet host material, where the electron-trapping Cr2+ ions take the high spin state (t32ge1g) rather than the low-spin state (t42g).

Development of persistent phosphor of Eu2+ doped Ba2SiO4 by Er3+ codoping based on vacuum referred binding energy diagram

We have developed the Ba2SiO4: Eu2+ -Er3+ persistent phosphor. The vacuum referred binding energy (VRBE) diagram of the Ba2SiO4 host with the 4f ground states of divalent and trivalent lanthanide ions in the host band gap was constructed from the obtained spectroscopic data and the Dorenbos's procedure. From the constructed diagram, the VRBE values of the conduction band (CB) bottom and valence band (VB) top were estimated to be −0.66 and −8.27 eV, respectively. From the energy gap between the CB bottom and 4f ground states of divalent lanthanide ions, we selected the Er3+ ion as an efficient co-dopant because the trap depth was estimated to be 0.64 eV, suitable for improving the persistent luminescence duration. The Eu2+-Er3+-codoped sample showed persistent luminescence intensity of over 0.32 mcd/m2 for 7 h duration. The initial persistent luminance intensity of the Eu2+-2%Er3+-codoped sample was found to be 250 times stronger than that of the only Eu2+-doped sample.

Formation of Deep Electron Traps by Yb3+ Codoping Leads to Super-Long Persistent Luminescence in Ce3+-Doped Yttrium Aluminum Gallium Garnet Phosphors.

The Y3Al2Ga3O12:Ce3+-Cr3+ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr3+ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr3+ and lanthanide ions, we selected Yb3+ as a deeper electron trapping center. The Y3Al2Ga3O12:Ce3+-Yb3+ phosphors show Ce3+:5d → 4f green persistent luminescence after blue light excitation. The formation of Yb2+ was confirmed by the increased intensity of absorption due to Yb2+:4f-5d at 585 nm during the charging process. This result indicates that the Yb3+ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found that the Yb3+ trap makes a much deeper electron trap with a 1.01 eV depth than the Cr3+ electron trap with a 0.81 eV depth. This deeper Yb3+ trap provides a much slower detrapping rate of filled electron traps than the Cr3+-codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce3+ and Yb3+ concentrations, the Y3Al2Ga3O12:Ce3+(0.2%)-Yb3+(0.1%) as-made transparent ceramic phosphor showed super-long persistent luminescence for over 138.8 h after blue light charging.

Vacuum Referred Binding Energy (VRBE)-Guided Design of Orange Persistent Ca3Si2O7:Eu2+ Phosphors.

Orange persistent phosphors of Ca3Si2O7 (CSO) doped with Eu2+ were strategically developed by codoping Sm3+ or Tm3+. First, a vacuum referred binding energy, VRBE, diagram of Ca3Si2O7 (CSO) was constructed from the measured spectroscopic data. By the zigzag curve of the divalent lanthanide ions in the VRBE diagram, Sm3+ and Tm3+ ions were predicted to be a suitable electron trap for the persistent luminescence. The initial persistent luminance of CSO:Eu2+-Sm3+ and CSO:Eu2+-Tm3+ was found to be 290 times and 9300 times stronger, respectively, compared with CSO:Eu2+. By optimizing Eu2+ and Tm3+ concentrations, the persistent luminescence duration on 0.32 mcd/m2 reached approximately 50 min in CSO:Eu2+-Tm3+. From the VRBE diagram and the persistent luminescence properties, we discuss the persistent mechanism including the charging process, detrapping process, and electron trapping centers.

Rapid and Energy-Saving Microwave-Assisted Solid-State Synthesis of Pr(3+)-, Eu(3+)-, or Tb(3+)-Doped Lu2O3 Persistent Luminescence Materials.

Persistent luminescence materials Lu2O3:R(3+),M (Pr,Hf(IV); Eu; or Tb,Ca(2+)) were successfully and rapidly (22 min) prepared by microwave-assisted solid-state synthesis (MASS) using a carbon microwave susceptor and H3BO3 as flux. Reaction times are reduced by up to 93% over previous synthetic methods, without special gases application and using a domestic microwave oven. All materials prepared with H3BO3 flux exhibit LuBO3 impurities that were quantified by Rietveld refinement from synchrotron radiation X-ray powder diffraction patterns. The flux does not considerably affect the crystalline structure of the C-Lu2O3, however. Scanning electron micrographs suggest low surface area when H3BO3 flux is used in the materials' synthesis, decreasing the amount of surface hydroxyl groups in Lu2O3 and improving the luminescence intensity of the phosphors. The carbon used as the susceptor generates CO gas, leading to complete reduction of Tb(IV) to Tb(3+) and partial conversion of Pr(IV) to Pr(3+) present in the Tb4O7 and Pr6O11 precursors, as indicated by X-ray absorption near-edge structure data. Persistent luminescence spectra of the materials show the red/near-IR, reddish orange, and green emission colors assigned to the 4f(n) → 4f(n) transitions characteristics of Pr(3+), Eu(3+), and Tb(3+) ions, respectively. Differences between the UV-excited and persistent luminescence spectra can be explained by the preferential persistent luminescence emission of R(3+) ion in the S6 site rather than R(3+) in the C2 site. In addition, inclusion of Hf(IV) and Ca(2+) codopants in the Lu2O3 host increases the emission intensity and duration of persistent luminescence due to generation of traps caused by charge compensation in the lattice. Photonic materials prepared by MASS with H3BO3 flux show higher persistent luminescence performance than those prepared by the ceramic method or MASS without flux. Color tuning of persistent luminescence in Lu2O3:R(3+),M provides potential applications in bioimaging as well as in solar cell sensitizers.

Effects of boric acid on structural and luminescent properties of BaAl2O4:(Eu2+, Dy3+) phosphors

Eu2+/Dy3+-codoped BaAl2O4 phosphors were prepared by conventional solid-state reaction with boric acid flux. The effects of boric acid on structural and luminescent properties of BaAl2O4:(Eu2+, Dy3+) were investigated. The crystallinity of BaAl2O4 improved with increasing amount of H3BO3. Incorporation of Eu2+ and Dy3+ ions into effective lattice sites was promoted by H3BO3 addition. As a result, Eu2+ emission in BaAl2O4 was greatly enhanced by H3BO3, and the duration of persistent luminescence increased with the amount of H3BO3. However, the decay lifetime of persistent luminescence was not strongly influenced by the amount of H3BO3.

Synthesis and Persistent Luminescence Mechanism of a Novel Orange Emitting Persistent Phosphor Sr5(BO3)3Cl:Eu2+

A series of Eu2+‐doped Sr5(BO3)3Cl phosphors were prepared successfully using a conventional solid‐state reaction method. The luminescent properties were studied systematically by utilizing photoluminescence spectra, decay curves, persistent luminescence spectra, and thermoluminescence glow curves. Energy transfer from host to emission center Eu2+ was affirmed. The orange persistent luminescence emission was observed for the first time. The optimal doping concentration of Eu2+ for persistent luminescence was experimentally to be approximately 0.5% and the orange persistent luminescence duration can persist about 15 min. On the basis of the experimental results, a model was constructed and the relevant mechanism of persistent luminescence was illustrated in detail. Two different ways of trapping the charge carriers were also discussed.

Understanding Persistent Luminescence: Rare-Earth- and Eu2+-doped Sr2MgSi2O7

Similar to many other Eu2+,RE3+-co-doped persistent luminescence materials, for Sr2MgSi2O7:Eu2+,RE3+ the initial intensity and duration of persistent luminescence was also found to depend critically on the rare-earth (RE) co-doping. An enhancement of 1 - 2 orders of magnitude in these properties could be obtained by Dy3+ co-doping whereas total quenching of persistent luminescence resulted from the use of Sm3+ and Yb3+. To solve this drastic disparity, the effects of the individual RE3+ ions were studied with thermoluminescence (TL) spectroscopy to derive information about the formation of traps storing the excitation energy. The charge compensation defects were concluded to be the origin of the complex TL glow curve structure. The tuning of the band gap of the Sr2MgSi2O7 host and especially the position of the bottom of the conduction band due to the Eu2+,RE3+ co-doping was measured with the synchrotron radiation vacuum UV (VUV) excitation spectra of the Eu2+ dopant. The model based on the evolution of the band gap energy with RE3+ co-doping was found to explain the intensity and duration of the persistent luminescence.

Influence of titanium and lutetium on the persistent luminescence of ZrO_2

Non-doped as well as titanium and lutetium doped zirconia (ZrO2) materials were synthesized via the sol-gel method and structurally characterized with X-ray powder diffraction. The addition of Ti in the zirconia lattice does not change the crystalline structure whilst the Lu doping introduces a small fraction of the tetragonal phase. The UV excitation results in a bright white-blue luminescence at ca. 500 nm for all the materials which emission could be assigned to the Ti3+eg → t2g transition. The persistent luminescence originates from the same Ti3+ center. The thermoluminescence data shows a well-defined though rather similar defect structures for all the zirconia materials. The kinetics of persistent luminescence was probed with the isothermal decay curve analyses which indicated significant retrapping. The short duration of persistent luminescence was attributed to the quasi-continuum distribution of the traps and to the possibility of shallow traps even below the room temperature.