Evaluation of optoelectronic response and Raman active modes in Tb³⁺ and Eu³⁺-doped gadolinium oxide (Gd₂O₃) nanoparticle systems

Rare earth oxide (Tb³⁺:Gd₂O₃ and Eu³⁺:Gd₂O₃) 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 Tb³⁺ doped systems signify intense blue-green (∝490 nm) and green (∝544 nm) emissions mediated by ⁵D₄ → ⁷F₆ and ⁵D₄ → ⁷F₅ transitional events; respectively. In the PL responses of Eu³⁺ doped nanoparticle systems, we also identify magnetically-driven ⁵D₀ → ⁷F₁ (∝591 nm) and electrically driven ⁵D₀ → ⁷F₂ (∝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. (orig.)