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Luminescence and photo-thermally stimulated defects creation processes are studied for a Pr3+-doped PbWO4 crystal at 4.2-400 K under excitation in the band-to-band, exciton, and charge-transfer transitions regions, as well as in the Pr3+-related absorption bands. Emission spectra of Pr3+ centers depend on the excitation energy, indicating the presence of Pr3+ centers of two types. The origin of these centers is discussed. The 2.03-2.06 eV emission, arising from the ¹D2→³H4 transitions of Pr3+ ions, is found to be effectively excited in a broad intense absorption band peaking at 4.2 K at 3.92 eV. By analogy with some other Pr3+-doped compounds, this band is suggested to arise from an electron transfer from an impurity Pr3+ ion to the crystal lattice W6+ or Pb2+ ions. The dynamics of the Pr3+-related excited states is clarified. In the PbWO4:Pr crystal studied, the concentration of single oxygen and lead vacancies as traps for electrons and holes is found to be negligible. [ABSTRACT FROM AUTHOR]

Photo- and X-ray-excited luminescence characteristics of Bi-doped LiLaP 4 O 12 phosphates with different bismuth contents (from 1 to 25 at% in the melt) are investigated in the 4.2–300 K temperature range and compared with the characteristics of the undoped LiLaP 4 O 12 phosphate. The broad 2.95 eV emission band of LiLaP 4 O 12 :Bi excited around 5.4 eV is found to arise from the bismuth dopant. Relatively large FWHM and Stokes shift of the emission band and especially the data on the low-temperature decay kinetics of the 2.95 eV emission and its temperature dependence, indicating a very small spin-orbit splitting energy of the corresponding excited state, allow the conclusion that this emission arises from the radiative decay of the triplet state of an exciton localized around a Bi 3+ ion. No spectral bands are observed, arising from the electron transitions between the energy levels of Bi 3+ ions. Phenomenological model is proposed for the description of the excited state dynamics of the Bi 3+ -related localized exciton in LiLaP 4 O 12 :Bi and the parameters of the triplet localized exciton state are determined. Keywords: Photoluminescence; Time-resolved spectroscopy; Excited states; Bi 3+ centers; LiLaP 4 O 12 :Bi powders [ABSTRACT FROM AUTHOR]

Photoluminescence of Y 2 O 3 :Bi nanopowder synthesized by the modified sol–gel method is studied using time-resolved luminescence spectroscopy in the 4.2–300 K temperature range. Bi 3+ ions are substituted for Y 3+ ions in two different crystal lattice sites, one having S 6 symmetry (Bi(S 6 )) and the other C 2 symmetry (Bi(C 2 )). The luminescence characteristics of these two centers are found to have strongly different electron–phonon interactions. The luminescence of Bi(S 6 ) and Bi(C 2 ) centers peak at 3.04 eV and 2.41 eV, respectively, and arise from the radiative decay of the triplet relaxed excited state (RES) of Bi 3+ ions. The model and structure of the RES, responsible for the luminescence of Bi(S 6 ) and Bi(C 2 ) centers in Y 2 O 3 :Bi, as well as radiative and nonradiative processes, taking place in the excited states of these centers, are investigated. The parameters of the triplet RES (the separation between the metastable and radiative levels and probabilities of radiative and nonradiative transitions from these levels) are determined. Low-temperature quenching of the triplet luminescence of these centers is explained by nonradiative quantum tunneling transitions from the metastable minima of their triplet RES to closely located defect- or exciton-related levels. [ABSTRACT FROM AUTHOR]

Highlights: [•] Luminescence spectra and decay kinetics for YAlO3:Bi3+ at 8–400K reported. [•] The ultraviolet (UV) emission only present in the spectrum of YAlO3:Bi3+. [•] The UV emission due to the triplet relaxed excited state (RES) of a Bi3+ ion. [•] The Bi3+ excited states dynamics and triplet RES parameters modelled. [•] Scintillation efficiency of YAlO3:Bi3+ is of 35–40% of that of BGO. [Copyright &y& Elsevier]