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 Bi^{2+ 2}P_1/2 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.

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Discovering light dosimeters that can function effectively from liquid nitrogen temperature to 700 K presents significant challenges. Such dosimeters facilitate a range of cutting-edge applications, including anti-counterfeiting measures at low temperature for cryo-preservation. To facilitate such discovery, stacked vacuum referred binding energy diagrams for the LiYGeO4 cluster of crystals have been first constructed. They offer a robust method for controlling both electron and hole trapping depth in the LiYGeO4 cluster of crystals. Wide temperature shifting of Bi2+ and Eu2+ thermoluminescence (TL) glow bands emerges from 200 to 500 K for LiYxLu1-xGeO4:0.01Bi3+ and LiYxLu1-xGeO4:0.01Bi3+, 0.001Eu3+, by changing x, facilitating conduction band tailoring. Wide temperature shifting of Bi4+ TL glow bands emerges from 300 to 700 K for LiYGezSi1-zO4:0.01Bi3+, by tuning z, facilitating valence band tailoring. TL glow band peaks near 135, 185, 232, and 311 K emerge in LiyNa1-yYGeO4: 0.001Bi3+. Particularly, the discovered Bi3+ or/and lanthanide modified LiYGeO4 cluster of crystals exhibit superior charge carrier storage capacity and minimal TL fading properties. For instance, the ratio of TL intensity of the optimized LiYGe0.75Si0.25O4:0.001Bi3+ to that of industrial BaFBr(I):Eu2+ is as high as ∼4. Interestingly, imaging of intense optically driven Bi3+ ultraviolet-A (UVA) luminescence has been validated in 254 nm energized LiY0.25Lu0.75GeO4:0.01Bi3+ with a 100 lux white LED illumination. Together with ZnS:Mn2+, LiTaO3:Bi3+, Sm3+, and Cs2ZrCl6:Sb3+ perovskites, the realization of wide range liquid nitrogen temperature to 700 K Bi3+ thermoluminescence in Bi3+ or/and lanthanide modified LiYGeO4 cluster of crystals with superior charge carrier storage capacity offers promising use for versatile anti-counterfeiting, information storage, and delayed x-ray imaging purposes.@en

Discovering energy storage materials with rationally controlled trapping and de-trapping of electrons and holes upon x-rays, UV-light, or mechanical force stimulation is challenging. Such materials enable promising applications in various fields, for instance in multimode anti-counterfeiting, x-ray imaging, and non-real-time force recording. In this work, photoluminescence spectroscopy, the refined chemical shift model, and thermoluminescence studies will be combined to establish the vacuum referred binding energy (VRBE) diagrams for the LiSc_1-xLu_xGeO₄ family of compounds containing the energy level locations of Bi²⁺, Bi³⁺, and the lanthanides. The established VRBE diagrams are used to rationally develop Bi³⁺ and lanthanides doped LiSc_1-xLu_xGeO₄ storage phosphors and to understand trapping and de-trapping processes of charge carriers with various physical excitation means. The thermoluminescence intensity of x-ray irradiated LiSc_0.25Lu_0.75GeO₄:0.001Bi³⁺,0.001Eu³⁺ is about two times higher than that of the state-of-the-art x-ray storage phosphor BaFBr(I):Eu²⁺. Particularly, a force induced charge carrier storage phenomenon appears in Eu³⁺ co-doped LiSc_1-xLu_xGeO₄. Proof-of-concept non-real-time force recording, anti-counterfeiting, and x-ray imaging applications will be demonstrated. This work not only deepens our understanding of the capturing and de-trapping processes of electrons and holes with various physical excitation sources, but can also trigger scientists to rationally discover new storage phosphors by exploiting the VRBEs of bismuth and lanthanide levels.

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Multimode luminescence relates to how charge carriers are transported and recombined in response to various physical excitations. It shows promising applications in many fields like advanced anti-counterfeiting, information storage and encryption. Enabling a stable single compound with multimode luminescence is a unique technology but still remains a challenge. Herein, a versatile and high-performance energy storage LiTaO₃:0.01Tb³⁺,xGd³⁺ perovskite is discovered by utilizing the interplay of electron-trapping defect levels and hole-trapping Tb³⁺. It combines an excellent charge carrier storage capacity (≈7 and 12 times higher than state-of-the-art BaFBr(I):Eu²⁺ and Al₂O₃:C), >1200 h storage duration, >40 h afterglow, efficient optically stimulated luminescence, persistent mechanoluminescence, and force-induced charge carrier storage features. Particularly, it well responds to various stimuli channels, i.e., wide-range X-rays to 850 nm infrared photons, thermal activation, mechanical force grinding, or compression. To elucidate this multimode luminescence, charge carrier trapping and release processes in LiTaO₃:0.01Tb³⁺,xGd³⁺ with various physical stimulations will be unraveled by combining the vacuum-referred binding diagram construction, spectroscopy, thermoluminescence, and mechanoluminescence techniques. The versatile and high-performance LiTaO₃:0.01Tb³⁺,xGd³⁺ enables promising proof-of-concept multimode luminescence applications in advanced anti-counterfeiting, flexible X-ray imaging, continuous compression force sensing, and non-real-time recording.

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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.

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Developing X-ray or UV-light charged storage and mechanoluminescence (ML) materials with high charge carrier storage capacity is challenging. Such materials have promising utilization in developing new applications, for example, in flexible X-ray imaging, stress sensing, or non-real-time recording. Herein, the study reports on such materials; Bi³⁺, Tb³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃ perovskite storage and ML phosphors. Their photoluminescence, thermoluminescence (TL), and ML properties are studied. The charge carrier trapping and release processes in the Bi³⁺, Tb³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃ are explained by using the constructed vacuum referred binding energy diagram of LiTaO₃ including the energy level locations of unintended defects, Tb³⁺, Bi³⁺, and Bi²⁺. The ratio of the TL intensity after X-ray charging of the optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ga³⁺, or LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ge⁴⁺ to that of the state-of-the-art BaFBr(I):Eu²⁺ is ≈1.2 and 2.7, respectively. Force induced charge carrier storage phenomena is studied in the Tb³⁺, Bi³⁺, Ga³⁺, or Ge⁴⁺ doped LiTaO₃. Proof-of-concept compression force distribution sensing and X-ray imaging is demonstrated by using optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ga³⁺ dispersed in a hard epoxy resin disc and in a silicone gel film. Proof-of-concept color-tailorable ML for anti-counterfeiting is demonstrated by admixing commercial ZnS:Cu⁺,Mn²⁺ with optimized LiTaO₃:0.005Bi³⁺,0.006Tb³⁺,0.05Ge⁴⁺ in an epoxy resin disc.

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Discovering UV-light or X-ray charged afterglow and storage phosphors with high charge carrier storage capacity remains challenging. Herein, a method is proposed by combining vacuum referred binding energy (VRBE) diagram construction and optimization of dopants’ concentration and compound synthesis. The refined chemical shift model, optical spectroscopy, and thermoluminescence will be combined to construct the VRBE diagram of LiTaO₃ with the lanthanide and bismuth charge transition levels. Based on the constructed VRBE diagram of LiTaO₃, Bi³⁺, and/or Ln³⁺ (Ln = Tb or Pr) doped LiTaO₃ will be studied. By combining Bi³⁺ with Tb³⁺, Pr³⁺, or Bi³⁺ itself, Bi³⁺ emerges to act as a ≈0.62 eV deep electron trap, while Tb³⁺, Pr³⁺, or Bi³⁺ acts as about 1.5 eV deep hole capturing and recombination centres. The VRBE in the Bi^{2+ 2}P_1/2 ground state will be derived by thermoluminescence study. Proof-of-concept X-ray imaging, compression force distribution monitoring, and color-tailoring for anti-counterfeiting will be demonstrated by using the developed Bi³⁺ and/or Ln³⁺ doped LiTaO₃. This work promotes the understanding of trap level locations and on the trapping and release processes of charge carriers in Bi³⁺ and/or lanthanides doped inorganic compounds for rational design of new afterglow and storage phosphors.

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It is challenging to obtain a material that can detect photons ranging from X-rays to infrared light. Such materials have promising use to develop advanced applications like in information storage, anticounterfeiting, or X-ray imaging. This article reports on such a material; LiTaO₃:xBi³⁺,yDy³⁺ perovskite phosphor. Experimental spectroscopy, thermoluminescence, and vacuum referred binding energy diagram (VRBE) construction are combined to study the trapping processes of charge carriers. The VRBEs in the ground or excited states of Bi³⁺ and Bi²⁺ are discussed. Bi³⁺ emerges to act as a ≈1.3 eV deep hole capturing center and it may possibly also act as a 0.80 ± 0.5 eV deep electron trapping center. A linear relation between the amount of stored charge carriers and a photochromic phenomenon both induced by X-rays or 254 nm UV-light charging appears. The stored charge carriers in LiTaO₃:xBi³⁺,yDy³⁺ are removed by heating or with an optically stimulated process with 365 nm UV light to 850 nm infrared laser. More than 3 or 40 h of Bi³⁺ and Dy³⁺ based white afterglow is measurable in LiTaO₃:0.005Bi³⁺,0.004Dy³⁺ after exposure to X-rays or 254 nm UV light. Proof-of-concept light detection applications like 2D information storage and anticounterfeiting or X-ray imaging are demonstrated by using the phtotochromic and white afterglow LiTaO₃:xBi³⁺,yDy³⁺ phosphors.

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