Pieter Dorenbos

Small bandgap scintillators have gained significant attention in recent years. Especially Cs4PbBr6 is an interesting material, mitigating the small Stokes shift-related problem of perovskites like CsPbBr3. In this work, optical and scintillation properties of Cs4PbBr6 single crystals are investigated as a function of temperature, with a detailed focus at 10 K. The Cs4PbBr6 single crystals were grown using the vertical Bridgman method. Due to incongruent melting, CsPbBr3 inclusions are formed, generating a 540 nm emission band. Prepairing Cs4PbBr6 via solid-state synthesis yields CsPbBr3-inclusion-free material, showing no green 540 nm emission band. In Cs4PbBr6 samples with and without CsPbBr3 inclusions, a new emission band at 610 nm ascribed to an unknown defect was found. Based on the presented experiments, an emission mechanism is proposed for Cs4PbBr6. This shows that both defects and CsPbBr3 inclusions play a role in the emission behavior of Cs4PbBr6 but only the CsPbBr3 inclusions are responsible for the 540 nm emission.

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.

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 LiSc1−xLuxGeO4 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 LiSc1−xLuxGeO4 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 LiSc0.25Lu0.75GeO4:0.001Bi3+,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 LiSc1−xLuxGeO4. 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.

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. Below this temperature, the light yield starts to decrease, which can be linked to the unusually large increase in the band gap energy of CsCu₂I₃.

Cs₄EuX₆ scintillators suffer from strong self-absorption and weak concentration quenching. Both can be avoided by Sm²⁺ doping. It improves the energy resolution, shortens the decay time and shifts the emission wavelength into the near-infrared.

The thermal quenching data of 5d emission from Eu²⁺ and Ce³⁺ and 4f emission from Pr³⁺, Eu³⁺, and Tb³⁺ are shown to be consistent with vacuum referred binding energy schemes. The scheme construction parameters of 170 different compounds are provided.

The VUV-UV-vis photoluminescence, X-ray radioluminescence, energy transfer dynamics of Ce ³⁺ and Eu ²⁺ in Sr ₂ MgSi ₂ O ₇ and the dependencies of Ce ³⁺ 4f–5d transitions on the local structure of Sr ₂ MgSi ₂ O ₇ , Ba ₂ MgSi ₂ O ₇ and BaMg ₂ Si ₂ O ₇ are discussed.

Professor Jurchescu, Dr. Wolszczak, Professor Burger, Dr. Bourret-Courchesne, and Professor Dorenbos introduce the Journal of Materials Chemistry C–Materials Advances themed collection in memoriam of Prof. Richard T. Williams.

Low temperature optical and scintillation characterisation of PEA₂PbBr₄ single crystals, based on which two potential scintillation mechanisms are proposed.

The trends in electronic structure of Bi³⁺ and Bi²⁺ as luminescent dopant in wide bandgap inorganic compounds and that of pure Bi-compounds for photocatalytic splitting of water are explored by determination of vacuum referred electron binding energies. Spectroscopic data combined with the chemical shift model from the luminescence field and data on flatband potentials in electrochemistry provide most of the needed data. Occasionally data from photoelectron spectroscopy is used. The trends in VRBE of Bi³⁺ and Bi²⁺ ground state and excited state levels resemble that of Ce³⁺ and Eu²⁺ lanthanides. To some extend a pure Bi-compound can be regarded as a 100% Bi³⁺ doped La-compound. This all will be demonstrated and an overview on Bi electronic structure is presented. Comparison of electronic structure for Bi as luminescent dopant in inorganic compounds with pure Bi-compounds entails also a comparison of two disciplines in electro-chemistry, that of luminescence materials and of photo-catalytic compounds.