Abstract
LiLa9(SiO4)6O2 (LLSO) crystals present an interesting host lattice with partially disordered apatite structure. Spectra of photoluminescence (PL) in region of 1.5–5.5 eV, PL excitation spectra (3–6 eV), X-ray excited luminescence and luminescence decay kinetics were measured at room temperature and T= 90 K in LLSO doped with Ce3+ (1%) and Pr3+ (1%) ions. Interconfigurational d→f transitions are observed in Ce3+ ions replacing La3+ in two cationic sites with different coordination environment. The excited 4fn-15d-states of Ce3+ ions are strongly dependent on local coordination environment. Intraconfigurational f→f transitions in visible (discrete PL spectrum) and interconfigurational d→f transitions in UV region (two broad bands in PL spectrum) are observed in LLSO:Pr3+. The photon cascade emission is not observed in Pr3+ ions, since 1S0 state is above excited 4fn-15d mixed-states zone or overlaps with it. Moreover, apart from RE3+ ions luminescence, low-temperature defect-related luminescence has been observed under UV and X-ray excitation.
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