•Structure–property relationship are established.•The CB edge shifts downward with increasing Sc or In content.•The 5d1 state of Pr3+ shifts to higher position in the forbidden gap.•The cooperative process of excitation from Pr3+ 5d to 4f levels is found.•The unwanted excited-state ionization of Pr3+ emission center is revealed.Pr3+-doped Lu3−xScxAl5O12 and Lu3−xInxAl5O12 (x=0, 0.025, 0.1, 0.25, 0.5, 0.75, 1, and 2) polycrystals are fabricated by the high-temperature solid state reaction method. Although X-ray excited luminescence measurements show that there is no positive contribution of Sc3+ or In3+ substitution on the scintillation efficiency, but the physical aspects of band-gap engineering such as the cooperative process of excitation and thermal ionization of 5d1 excited state are illustrated in this study. We employ a combination of optical diffuse reflectance, photoluminescence, decay kinetic, thermoluminescence experiments to reveal the influence of Sc3+ or In3+ substitution on electronic structure and luminescent properties in Pr3+-doped lutetium aluminate garnet.

Single crystals of undoped and 0.5 at.% Ce3+-doped Tb2.2Lu0.8Al5O12 (LuTbAG) with dimensions of up to ∅25 × 30 mm3 have been successfully grown by the Czochralski pulling method. After the single-phase was confirmed using X-ray diffraction analysis, the absorption coefficient of the undoped LuTbAG was investigated. By using the results of Rietveld refinement and electron probe micro-analysis, the site occupations in undoped and Ce-doped LuTbAG crystals were indirectly revealed. The optical and scintillation characteristics of Ce3+-doped LuTbAG crystals were investigated in detail. In the transmittance spectra, Ce3+-doped crystals showed not only absorption bands at around 340 and 459 nm which are ascribed to the transition from the 4f ground state to the 5d excited state of Ce3+, but also the typical 4f–4f absorption of Tb3+. Under X-ray and UV excitation, strong emission peaks at 530 nm and 565 nm because of the Ce3+ 5d–4f transition and the line emission traces of 4f–4f transitions featuring Tb3+ were both observed for the Ce3+ doped crystal. The scintillation efficiency of the LuTbAG:Ce crystal under X-ray excitation was about two times larger than that of a BGO commercial crystal measured under the same conditions. Pulsed X-ray luminescence measurements showed two exponential decay components of 1.8 μs and 161 μs. These initial results make the LuTbAG:Ce crystal an attractive and promising scintillator for X-ray detection. In addition, the point defects in the undoped and Ce-doped LuTbAG crystals were investigated by a wavelength-resolved thermoluminescence technique.

The Lu0.8Sc0.2BO3 polycrystalline powders doped with 1 at%Ce3+ and co-doped with Ca2+, Mg2+, or Sr2+ with varying concentration were fabricated by conventional solid-state reaction method. We applied X-ray diffraction, optical diffuse reflectance spectrum, luminescent spectra under UV and X-ray excitation, fluorescence decay time and X-ray absorption near edge spectroscopy to study the effects of divalent ions co-doping on the Lu0.8Sc0.2BO3:Ce scintillation materials. Through experiments, the influence of divalent ions co-doping strategy on scintillation efficiency and the action mechanism were revealed.Highlights► No positive contribution of the Me2+ ions on the scintillation efficiency was found. ► Parasite emission located around 380–400 nm for certain Me2+ co-doping ions. ► The Ce3+-distorted luminescence center formed after Me2+ co-doping. ► Point defects and Ce4+ concentration increasing were responsible for the deterioration.

•Energy transfer from 5d state of Pr3+ to the 4f state of Gd3+is proved.•Non-radiative relaxation from 5d to 4f state of Pr3+ is evidenced.•Localized recombination processes from electron traps to 4f levels of Pr3+ occurs.•Pr3+ is an ineffective activation ion for Gd-based multicomponent aluminate garnets.(GdxLu3−x)Ga3Al2O12:0.3 at.%Pr (x = 0.025, 0.05, 0.1, 0.2, 0.4, 0.6) (GLGAG:Pr) polycrystalline powders are prepared by solid-state reaction method. To better understand the luminescence mechanism, the optical diffuse reflectance, photoluminescence emission and excitation, X-ray excited luminescence spectra and decay kinetics of GLGAG:Pr were investigated in detailed, allowing the determination of energy transfer from 5d state of Pr3+ to 4f state of Gd3+, and the non-radiative relaxation from 5d to 4f state of Pr3+. Besides, the former process plays more negative role in the emission quenching of GLGAG:Pr than later one. Pr3+ ion is regarded as an ineffective activation ion in Gd-based multicomponent aluminate garnets. In addition, the wavelength-resolved thermoluminescence spectra of GLGAG:Pr were studied after UV and X-ray irradiation. It is revealed that the localized recombination processes from electron traps to lower lying 4f levels of Pr3+ occurs without populating the higher 5d levels of Pr3+.Graphical abstract