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.

Background: Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of Lu176 forbidden β decays are very limited and lack formulation of shape factors. A direct precise measurement of its Q value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments. Purpose: Perform the first precision measurements of Lu176β-decay spectra and attempt the observation of its electron capture decays, as well as perform the first precision direct measurement of the Lu176β-decay Q value. Compare the shape of the precisely determined experimental β spectra to theoretical calculations, and compare the end point energy to that obtained from an independent Q value measurement. Method: The Lu176β-decay spectra measurements and the search for electron capture decays were performed with an experimental setup that employed lutetium-containing scintillator crystals and a NaI(Tl) spectrometer for coincidence counting. The β decay Q value was determined via high-precision Penning trap mass spectrometry (PTMS) with the LEBIT facility at the National Superconducting Cyclotron Laboratory. The β-spectrum calculations were performed within the Fermi theory formalism with nuclear structure effects calculated using a shell model approach. Results: Both β transitions of Lu176 were experimentally observed and corresponding shape factors formulated in their entire energy ranges. The search for electron capture decay branches led to an experimental upper limit of 6.3×10-6 relative to its β decays. The Lu176β-decay and electron capture Q values were measured using PTMS to be 1193.0(6) and 108.9(8) keV, respectively. This enabled precise β end point energies of 596.2(6) and 195.3(6) keV to be determined for the primary and secondary β decays, respectively. The conserved vector current hypothesis was applied to calculate the relativistic vector matrix elements. The β-spectrum shape was shown to significantly depend on the Coulomb displacement energy and on the value of the axial vector coupling constant gA, which was extracted according to different assumptions. Conclusion: The implemented self-scintillation method has provided unmatched observations of Lu176, independently validated by the first direct measurements of its β-decay Q value by Penning trap mass spectrometry. Theoretical study of the main β transition led to the extraction of very different effective gA and log10f values, showing that a high-precision description of this transition would require a realistic nuclear structure with nucleus deformation.

RE₂O₂S:Eu³⁺-Ln³⁺ (RE = La, Gd, Y, Lu; Ln = Pr, Tb) samples were prepared by a solid-state reaction method to develop new red persistent phosphors and to demonstrate the hole detrapping mechanism. All Eu³⁺-singly doped RE₂O₂S show very weak thermoluminescence (TL) glow peaks, while by codoping Pr³⁺ or Tb³⁺ ions, additional strong TL peaks were observed. In the TL spectra and persistent luminescence (PersL) spectra, only Eu³⁺ luminescence lines were observed, but there was no Pr³⁺ and Tb³⁺ luminescence. From the PersL excitation spectra, it is found that PersL is caused after excitation to the charge transfer state of Eu²⁺-S^- in which the hole is in the valence band. These results show that Eu³⁺ acts as a recombination center and Pr³⁺ and Tb³⁺ ions act as hole trap centers. The deeper hole trap depth of Pr³⁺ than that of Tb³⁺ and the RE dependence of hole trap depth are explained using a vacuum referred binding energy diagram considering the nephelauxetic effect. La₂O₂S:Eu³⁺-Pr³⁺ was the best composition among the samples as a persistent phosphor at ambient temperature, showing strong red persistent luminescence in a short time range (>100 mcd/m² for a few seconds).

Cationic tuning for lanthanide (Ce³⁺/Pr³⁺)-activated inorganic phosphors with stable, efficient, and fast-decay 5d-4f emissions has emerged as an important strategy toward the continuing pursuit of superior scintillators. The in-depth understanding of the cationic effects on photo- and radioluminescence of lanthanides Ce³⁺ and Pr³⁺ centers is requisite for the rational cationic tuning. Here, we perform a systematic study on the structure and photo- and X-ray radioluminescence properties of K₃RE(PO₄)₂:Ce³⁺/Pr³⁺ (RE = La, Gd, and Y) phosphors to elucidate the underlying cationic effects on their 4f-5d luminescence. By using the Rietveld refinements, low-temperature synchrotron-radiation vacuum ultraviolet-ultraviolet spectra, vibronic coupling analyses, and vacuum-referred binding energy schemes, the origins of lattice parameter evolutions, 5d excitation energies, 5d emission energies, and Stokes shifts as well as good emission thermal stabilities of K₃RE(PO₄)₂:Ce³⁺ systems are revealed. In addition, the correlations of Pr³⁺ luminescence to Ce³⁺ in the same sites are also discussed. Finally, the X-ray excited luminescence manifests that the K₃Gd(PO₄)₂:1%Ce³⁺ sample possesses a light yield of ∼10,217 photons/MeV, indicating its potentiality toward X-ray detection application. These results deepen the understanding of cationic effects on Ce³⁺ and Pr³⁺ 4f-5d luminescence and inspire the inorganic scintillator development.

Currently only Eu²⁺-based scintillators have approached the light yield needed to improve the 2% energy resolution at 662 keV of LaBr₃:Ce³⁺,Sr²⁺. Their major limitation, however, is the significant self-absorption due to Eu²⁺. CsCu₂I₃ is an interesting new small band gap scintillator. It is nonhygroscopic and nontoxic, melts congruently, and has an extremely low afterglow, a density of 5.01 g/cm³, and an effective atomic number of 50.6. It shows self-trapped exciton emission at room temperature. The large Stokes shift of this emission ensures that this material is not sensitive to self-absorption, tackling one of the major problems of Eu²⁺-based scintillators. An avalanche photo diode, whose optimal detection efficiency matches the 570 nm mean emission wavelength of CsCu₂I₃, was used to measure pulse height spectra. From the latter, a light yield of 36 000 photons/MeV and energy resolution of 4.82% were obtained. The scintillation proportionality of CsCu₂I₃ was found to be on par with that of SrI₂:Eu²⁺. Based on temperature-dependent emission and decay measurements, it was demonstrated that CsCu₂I₃ emission is already about 50% quenched at room temperature. Using temperature-dependent pulse height measurements, it is shown that the light yield can be increased up to 60 000 photons/MeV by cooling to 200 K, experimentally demonstrating the scintillation potential of CsCu₂I₃.

The benefits of doping Cs₄EuBr₆ and Cs₄EuI₆ with Sm²⁺ are studied for near-infrared scintillator applications. It is shown that undoped Cs₄EuI₆ suffers from a high probability of self-absorption, which is almost completely absent in Cs₄EuI₆:2% Sm. Sm²⁺ doping is also used to gain insight in the migration rate of Eu²⁺ excitations in Cs₄EuBr₆ and Cs₄EuI₆, which shows that concentration quenching is weak, but still significant in the undoped compounds. Both self-absorption and concentration quenching are linked to the spectral overlap of the Eu²⁺ excitation and emission spectra which were studied between 10 K and 300 K. The scintillation characteristics of Cs₄EuI₆:2% Sm is compared to that of the undoped samples. An improvement of energy resolution from 11% to 7.5% is found upon doping Cs₄EuI₆ with 2% Sm and the scintillation decay time shortens from 4.8 s to 3.5 s in samples of around 3 mm in size.

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.

Due to recent development in detector technology, photon-counting computed tomography (PCCT) has become a rapidly emerging medical imaging technology. Current PCCT systems rely on the direct conversion of X-ray photons into charge pulses, using CdTe, CZT, or Si semiconductor detectors. Indirect detection using ultrafast scintillators coupled to silicon photomultipliers (SiPM) offers a potentially more straightforward and cost-effective alternative. In this work a new 2D perovskite scintillator, benzylamonium lead bromide (BZA)₂PbBr₄, is experimentally characterised as function of temperature. The material exhibits a 4.2 ns decay time under X-ray excitation at room temperature and a light yield of 3700 photons/MeV. The simulation tool developed by Van der Sar et al. was used to model the pulse trains produced by a SiPM-based (BZA)₂PbBr₄ detector. The fast decay time of (BZA)₂PbBr₄ results in outstanding count-rate performance as well as very low statistical fluctuations in the simulated pulses. These features of (BZA)₂PbBr₄, combined with its cost-effective synthesis make (BZA)₂PbBr₄ very promising for PCCT.