Optical and Structural Characterization of Terbium-Doped Y2SiO5 Phosphor Particles

The structural and the optical properties of terbium-doped yttrium oxyorthosilicate phosphor particles were analyzed. The samples were prepared through an aqueous sol-gel route and investigated in a large doping concentration range (ranging from 0.001% to 10%). The structural properties were studied by joint approach of X-ray measurements and Raman analysis, revealing the same principal structural phase (C2/c space group) independently of the Tb concentration. Radio luminescence measurements, excitation of photoluminescence, and time-resolved luminescence indicated a very efficient charge transfer mechanism from the excited level D-5(3) to D-5(4) level of Tb3+. A simple three-level kinetics model was applied to explain the experimental data and to give an estimation of the efficiency of the charge transfer process as a function of terbium doping. Finally, we give an estimation of the high absolute fluorescence quantum yield (0.95) for the sat D-5(4) recombinations, almost independent of the Tb concentrations, showing that, from this level, there are no efficient nonradiative channels. The results disclose the heavy Tb-doped Y2SiO5 matrix as good candidate for the development of efficient UV light-emitting-diode-excited green phosphor in mercury-free fluorescent lamps and for a new generation of scintillator panels for X-ray radiography.