Luminescence of Excitons and Antisite Defects in Lu_(3)Al_(5)O_(12):Ce Single Crystals and Single-Crystal Films

摘要

The luminescence of excitons and antisite defects (ADs) was investigated, as well as the specific features of the excitation energy transfer from excitons and ADs to the activator (Ce~(3+) ion) in phosphors based on Lu_(3)Al_(5)O_(12):Ce (LuAG:Ce) single crystals and single-crystalline films, which are characterized by significantly different concentrations of ADs of the Lu_(Al)~(3+) type and vacancy-type defects. The luminescence band with (lambda)_(max) velence 249 nm in LuAG:Ce single-crystal films is due to the luminescence of self-trapped excitons (STEs) at regular sites of the garnet lattice. The excited state of STEs is characterized by the presence of two radiative levels with significantly different transition probabilities, which is responsible for the presence of two excitation bands with (lambda)_(max) velence 160 and 167 nm and two components (fast and slow) in the decay kinetics of the STE luminescence. In LuAG:Ce single crystals, in contrast to single-crystal films, the radiative relaxation of STEs in the band with (lambda)_(max) velence 253.5 nm occurs predominantly near Lu_(Al)~(3+) ADs. The intrinsic luminescence of LuAG:Ce single crystals at 300 K in the band with (lambda)_(max) velence 325 nm (tau velence 540 ns), which is excited in the band with (lambda)_(max) velence 175 nm, is due to the radiative recombination of electrons with holes localized near Lu_(Al)~(3+) ADs. In LuAG:C e single crystals, the excitation of the luminescence of Ce~(3+) ions occurs to a large extent with the participation of ADs. As a result, slow components are present in the luminescence decay of Ce~(3+) ions in LuAG:Ce single crystals due to both the reabsorption of the UV AD luminescence in the 4f-5d absorption band of Ce~(3+) ions with (lambda)_(max) velence 340 nm and the intermediate localization of charge carriers at ADs and vacancy-type defects. In contrast to single crystals, in phosphors based on LuAG:Ce single-crystal films, the contribution of slow components to the luminescence of Ce~(3+) ions is significantly smaller due to a low concentration of these types of defects.