Evaluation of optoelectronic response and Raman active modes in Tb~(3+) and Eu~(3+) -doped gadolinium oxide (Gd_2O_3) nanoparticle systems

摘要

Rare earth oxide (Tb~(3+):Gd_2O_3 and Eu~(3+):Gd_2O_3) nanophosphors are exploited through spectroscopic and microscopic tools with special emphasis on D-F mediated radiative emission and Raman active vibrational modes. Powder X-ray diffraction measurements have revealed cubic crystal structure of the nanosystems and with an average crystallite size varying between ～3.2 and 4.8 nm. Photoluminescence (PL) spectra of Tb~(3+) doped systems signify intense blue-green (～490nm) and green (～ 544 nm) emissions mediated by ~5D_4 → ~7F_6 and ~5D_4 → ~7F_5 transitional events; respectively. In the PL responses of Eu~(3+) doped nanoparticle systems, we also identify magnetically-driven ~5D_0 → ~7F_1 (～591 nm) and electrically driven ~5D_0 → ~7F_2 (～619 nm) radiative features which seem to improve with increasing doping level. However, the magnitude of Judd-Ofelt (J-O) intensity parameters (Ω_(2, 4)), is significantly lowered for the high doping cases. Raman spectra of the undoped and RE doped systems exhibited several A_g and F_g modes in the range of Raman shift ～ 100-600 cm~(-1). In the Raman spectra, the peaks located at ～355 cm~(-1) are assigned to the mixed mode of F_g + A_g, the line width of which was found to increase with RE doping. Moreover, owing to the enhanced defect concentration in the doped systems than its undoped counterpart, we anticipate a faster phonon relaxation and consequently, a suppression of phonon lifetime in the former case.