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•VRBEs in the Bi2+ 2P1/2 ground state in NaYGeO4 and NaLuGeO4 were experimentally determined by thermoluminescence study.•Electron liberation from Bi2+ has been evidenced.•Fully ...control of Bi3+ trapping depth via conduction band engineering.•Rational design of new Bi3+-based afterglow phosphor.
It is challenging to rational design persistent luminescence and storage phosphors with high storage capacity of electrons and holes after X-ray charging. Such phosphors have potential applications in anti-counterfeiting and X-ray imaging. Here we have combined vacuum referred binding energy diagram (VRBE) construction, photoluminescence spectroscopy, and thermoluminescence to study the trapping processes of charge carriers in NaYGeO4. In NaYGeO4:0.004Bi3+ and NaYGeO4:0.004Bi3+,0.005Ln3+ (Ln = Tb or Pr), Bi3+ appears to act as a shallow electron trap, while Bi3+ and Ln3+ act as deep hole trapping and recombination centres. We will show how to experimentally determine the VRBE in the Bi2+ 2P1/2 ground state in NaYGeO4 and NaLuGeO4 by thermoluminescence study. The electron trap depth produced by Bi3+ codopant in NaLu1-xYxGeO4:0.003Bi3+,0.008 Tb3+ can be adjusted, by increasing x, resulting in conduction band engineering. By combining Bi3+ as an electron trap and Bi3+ and Tb3+ as the hole traps, excellent X-ray charged afterglow phosphors were developed. The integrated TL intensity of the optimized NaYGeO4:0.004Bi3+ and NaYGeO4:0.003Bi3+,0.008Tb3+ after exposure to X-rays is about 4.5 and 1.1 times higher than that of the state-of-the-art BaFBr(I):Eu2+ storage phosphor. Intense initial Tb3+ 4f → 4f afterglow appears in NaYGeO4:0.003Bi3+,0.008Tb3+ and more than 40 h afterglow is measurable in NaYGeO4:0.004Bi3+ and NaYGeO4:0.003Bi3+, 0.008 Tb3+ after X-ray charging. We will show proof-of-concept anti-counterfeiting and X-ray imaging applications by using the developed afterglow phosphors and CsPbI3 quantum dots. This work not only provides experimental evidence on the VRBE in the Bi2+ 2P1/2 ground state in NaYGeO4, but also shows how to design and develop good afterglow phosphors for anti-counterfeiting and X-ray imaging by deeply studying and controlling the trapping processes of charge carriers in bismuth and/or lanthanides doped inorganic compounds.
Developing X-ray charged dosimeters with excellent charge carrier storage capacity and stability is challenging. Such energy storage dosimeters have fascinating use in developing novel applications, ...for instance, in radiation detection, advanced multimode anti-counterfeiting, and flexible X-ray imaging of curved objects. Herein, novel LiTaO3:Ln3+,Eu3+ (Ln=Tb or Pr) perovskite dosimeters are developed by combining the vacuum referred binding energy (VRBE) diagram of LiTaO3 and the optimization of dopant’s concentration and compound synthesis condition.
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•Eu3+ was evidenced as a good electron trapping centre.•Excellent LiTaO3:Ln3+,Eu3+ (Ln = Tb or Pr) dosimeters were rationally developed.•Charge carriers can be stored more than 1000 h.•New and advanced X-ray imaging application for curved objects was realized.•Promising and advanced anti-counterfeiting applications were demonstrated.
Developing X-ray charged dosimeters with excellent charge carrier storage capacity and stability is challenging. Such energy storage dosimeters have fascinating use in developing novel applications, for instance, in radiation detection, advanced multimode anti-counterfeiting, and flexible X-ray imaging of curved objects. Herein, novel LiTaO3:Ln3+,Eu3+ (Ln = Tb or Pr) perovskite dosimeters are reported by combining the vacuum referred binding energy (VRBE) diagram of LiTaO3 and the optimization of dopant’s concentration and compound synthesis condition. Based on the VRBE diagram prediction, charge carrier capturing and de-trapping processes in Eu3+ and/or Ln3+ (Ln = Tb or Pr) doped LiTaO3 will be studied to unravel the role of Eu3+ as a good electron trapping centre and to discover a record storage phosphor. The ratios of the thermoluminescence intensity of the optimized LiTaO3:0.005Tb3+,0.001Eu3+ to that of the state-of-the-art BaFBr(I):Eu2+, Al2O3:C, or NaLuF4:Tb3+ are 5.2, 8.8, or 2.8, respectively. The charge carriers can be stored more than 1000 h in LiTaO3:0.005Tb3+,0.001Eu3+. Proof-of-concept anti-counterfeiting application will be demonstrated by combining the colour-tailorable photoluminescence, afterglow, thermally, or optically stimulated luminescence in LiTaO3:0.005Tb3+,xEu3+ and LiTaO3:0.005Pr3+,0.001Eu3+. Multimode anti-counterfeiting application will be proposed by combining a high absolute X-ray scintillation light yield of 19000 ± 1800 ph/MeV of LiTaO3:0.005Tb3+,0.001Eu3+. Proof-of-concept flexible X-ray imaging application will be demonstrated by using the optimized LiTaO3:0.005Tb3+, 0.001Eu3+ dispersed in a silicone gel film.
The afterglow intensity of AlMgGaO4: Cr3+ has been enhanced by co-doping rare earth ions. The HRBE and VRBE diagram of the rare earth ions are constructed to determine the ground state energy level ...position of 4f in the forbidden band. The activation energy Ex is calculated to be 6.41 eV according to the diffuse reflection spectrum of AlMgGaO4, and the 4f level position of Eu2+ is obtained by the charge transfer band of Eu3+, whereby the ground state energy level position of all the divalent rare earth ions are determined. The energy difference between the ground state energy level of Eu3+ ion and Eu2+ ion are obtained by the centroids shift of the 5d energy level of Ce3+, and the ground state energy level position of all the trivalent rare earth ions are determined. The 4f energy levels of Eu2+, Sm2+ and Yb2+ are calculated to be 1.65, 0.4 and 1.21 eV below the conduction band, respectively, which can be used as energy storage levels of Cr3+. Then the near-infrared afterglow phosphors AlMgGaO4:0.03Cr3+, Ln3+ (Ln = Eu, Sm, Yb) are synthesized, and the afterglow properties are studied carefully. With Eu3+/Sm3+/Yb3+ concentrations increasing, the afterglow intensity is enhanced, and the intensity of thermoluminescence increases gradually and shifts to the high temperature, which indicates that the trap energy level of the phosphor is enriched with the increase of rare earth ion concentration. The results prove that constructing VRBE diagram is an effective way to select rare earth ions to enhance the afterglow intensity.
Discovering bismuth based smart materials that can respond to thermal, mechanical, and wide range X-ray to infrared photon excitation remains a challenge. Such materials have various uses like in ...advanced information encryption. In this work, valence state change between Bi2+, Bi3+, and Bi4+, and the dual role of Bi3+ in trapping electrons and holes have been studied in Bi3+ or/and Ln3+ (Ln=Tb or Pr) doped LiScGeO4 family of compounds by vacuum referred binding energy (VRBE) diagram construction, thermoluminescence, and spectroscopy. Electron release from Bi2+ has been evidenced. It can be used to experimentally determine the VRBE in the Bi2+ 2P1/2 ground state and to realize Bi3+ negative quenching luminescence. Particularly, a new force induced charge carrier storage phenomenon has been discovered for non-real-time force recording. Wide range of emission tailorable afterglow, unique Bi3+ ultraviolet-A, white, and infrared afterglow have been demonstrated by using Bi3+ as a hole trapping and recombination center and using energy transfer processes from Bi3+ to Tb3+, Pr3+, Dy3+, or Cr3+. Proof-of-concept advanced anti-counterfeiting, information encryption, and X-ray imaging will be demonstrated. This work not only develops smart storage phosphors, but more importantly unravels the valence change between Bi2+, Bi3+, or Bi4+ and how it can affect the trapping and release of charge carriers with thermal, optical, or mechanical excitation. This work therefore can promote the discovery and development of Bi3+ based smart materials for various applications.
Discovering bismuth based smart materials that can respond to thermal, mechanical, and wide range X-ray to infrared photon excitation remains a challenge. Such materials have various uses like in advanced information encryption. In this work, valence state change between Bi2+, Bi3+, and Bi4+, and the dual role of Bi3+ in trapping electrons and holes have been studied in Bi3+ or/and Ln3+ (Ln=Tb or Pr) doped LiScGeO4 family of compounds by vacuum referred binding energy (VRBE) diagram construction, thermoluminescence, and spectroscopy. Electron release from Bi2+ has been evidenced.
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Structural and optical properties of MGa2S4 (M = Mg, Zn, Ca, Sr, Ba) compounds have been compared, and the vacuum referred binding energy (VRBE) schemes were constructed for the lanthanide ions in ...the iso-structural compounds CaGa2S4 and SrGa2S4 employing literature data. The VRBE of an electron in the 5d excited state of Eu2+ was found at 0.75 and 0.97 eV below the bottom of the conduction band (CB) in CaGa2S4:Eu and SrGa2S4:Eu, respectively. Such differences explains the unexpected higher thermal quenching temperature reported for Eu2+-doped SrGa2S4 (T50% = ∼475 K) compared to Eu2+-doped CaGa2S4 (T50% = 400 K) The significantly lower VRBE at the CB-bottom in CaGa2S4 versus SrGa2S4 may be explained by the shorter Ga-S bond lengths in SrGa2S4.
Yb3+-doped phosphors have characteristic near-infrared (NIR) emissions, but their applications in phosphor-converted light-emitting-diodes (pc-LEDs) and Si solar cells are limited due to their ...mismatching excitation spectra. Here, we selected nitride La3Si6N11 (LSN) as host material to achieve Yb3+ NIR emission upon low-energy charge transfer (CT) excitation. The obtained phosphor LSN:Yb3+ has a broad CT excitation band ranging from 250 to 500 nm and narrowband NIR emissions ranging from 950 to 1100 nm centered at 983 nm. On the basis of spectral data, the vacuum referred binding energies (VRBE) schemes are constructed to locate energy levels of all lanthanide ions in LSN. We also fabricated NIR pc-LED device using 395 nm LED chip to demonstrate the potential applications of LSN:Yb3+ phosphors.
Based on the estimating methods of charge transfer energy, we selected La3Si6N11 as host material for Yb3+ doping to get near-infrared phosphor under low-energy charge transfer excitation. The potential application in phosphor-converted light-emitting-diodes (pc-LEDs) is demonstrated feasible and the vacuum referred binding energy (VRBE) schemes were conducted to give a reference of the luminescence properties of all Ln2+ and Ln3+ at any La-site in LSN. Display omitted
Lu2O3:Pr,Ti storage phosphors were prepared by means of high temperature (1700°C) sintering both in a reducing atmosphere of the N2-H2 mixture (3:1 by volume) and in ambient air. Their ...thermoluminescent (TL) properties were presented and discussed. Pr singly-doped material showed only very inefficient TL. Ti co-doping boosted the TL efficacy, and the most potent TL was observed for ceramics containing 0.05mol% of Pr and 0.007mol% of Ti and made in the reducing atmosphere. Samples prepared in air produced noticeably less intense TL. The glow curves of both materials consisted of one broad asymmetric band with the maximum around 357°C for the heating rate of 4.7°C/s. The glow peaks could be fitted with three (reduced samples) or two (air-sintered) components. The latter lacked the high-temperature part of TL compared to the former. Tmax-Tstop experiments indicated that the TL is connected with continuous distribution of trap depths, which were estimated to cover the range of ~ 1.7 to 2.3eV, and their specific values were slightly dependent on the methodology. Anomalous dependence of the TL intensity on the heating rate made the semi-localized transition the likely mechanism affecting the TL properties of Lu2O3:Pr,Ti ceramics. The collected data allowed to construct vacuum referred binding energy (VRBE) level scheme with Pr3+ and Ti3+/4+ energy levels in the band gap of Lu2O3 host that could explain the TL mechanism in Lu2O3:Pr,Ti ceramics.
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Persistent phosphors are widely investigated in indications, bio‐imaging, information storage, and anticounterfeiting. However, it remains a challenge to develop highly stable persistent phosphors ...with abundant and widely distributed traps. Here, a Ba0.58Sr0.4Al3Si3O4N5:0.02Yb2+ (Ba0.6Sr0.4Al3Si3O4N5:Yb2+) persistent phosphor with an excellent persistent luminescence (PersL) time of 383 min is reported before decaying to 0.32 mcd m−2 due to the existence of abundant intrinsic electron traps. Ba0.6Sr0.4Al3Si3O4N5:Yb2+ owns a trap distribution ranging from 0.41 to 1.04 eV and has a remarkably broad full width at half maximum (FWHM) of TL curve (169 K) among currently reported persistent phosphors. The robust stability of Ba0.6Sr0.4Al3Si3O4N5:Yb2+ is evidenced by immersing in hot water and annealing at the high temperature for different time, which showed PersL retention rates of over 90%. Temperature‐assisted information storage in this persistent phosphor is successfully demonstrated. Furthermore, a step‐by‐step write‐in method is implemented in anticounterfeiting, and the coded information can be optionally decoded at different temperatures due to the wide trap distribution in Ba0.6Sr0.4Al3Si3O4N5:Yb2+. This work demonstrates highly stable oxynitride persistent phosphors with widely distributed traps show great promise in information storage, anticounterfeiting, and photodetectors.
A stable oxynitride persistent phosphor resistance to high‐temperature and high‐humidity containing widely distributed traps, which originates from the abundant intrinsic defects, shows great potential in information storage, anticounterfeiting, and photodetectors.
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