Excitation power and Er3+ concentration effect on the color quality parameters in Y2O3:Er3+/Yb3+/Tm3+ nanophosphors

Y2O3 nanocrystalline phosphors doped with Er3 + / Yb3 + / Tm3 + ions were prepared using thermal decomposition technique at 500°C. Pure cubic phase of Y2O3 with an average crystallite size ∼29 ± 4 nm was determined from x-ray diffraction and high-resolution transmission electron microscope measurements. Their upconversion luminescence spectra were measured under 975-nm laser diode excitation at room temperature. A bright blue emission was simultaneously observed at 480 nm due to the G41 → H63 transition of Tm3 + ions, with the green (550 nm) and red (670 nm) emissions due to the H11/22, S3/24 → I15/24 and F9/24 → I15/24 transitions of Er3 + ions, respectively. Relative emission intensities of these colors were significantly affected by the Er3 + concentration as well as the excitation power density of 975-nm laser light. Color quality parameters and the color tuning abilities were determined from the Commission International de I’Echairage 1931 chromaticity diagram analysis, color rendering index, and their correlated color temperature values. A careful color tuning from cool to warm white light in Y2O3 : Er3 + / Yb3 + / Tm3 + phosphors was achieved by controlling both the doping concentration of Er3 + ions and the excitation power density of the 975-nm laser light.