Luminescence of LiLa_9(SiO_4)60_2 Silicate Crystals Doped with Ce~(3+) and Pr~(3+) Ions

摘要

LiLa_9(SiO_4)_6O_2 (LLSO) crystals present an interesting host lattice with partially disordered apatite structure. Spectra of photo luminescence (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 Ce~(3+) (1%) and Pr~(3+) (1 %) ions. Interconfigurational d→f transitions are observed in Ce~(3+) ions replacing La~(3+) in two cationic sites with different coordination environment. The excited 4f~(-1)5d-states of Ce~(3+) ions are strongly dependent on local coordination environment. Intracontigurational 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:Pr~(3+). The photon cascade emission is not observed in Pr~(3+) ions, since ~1S_0 state is above excited 4f~(n-1)5d mixed-states zone or overlaps with it. Moreover, apart from RE~(3+) ions luminescence, low-temperature defect-related luminescence has been observed under UV and X-ray excitation.