Judd-Ofelt spectroscopic properties of Er3+-doped NaLa(WO4)2 polycrystalline powder

Abstract

Er3+-doped NaLa(WO4)2 is a promising phosphor material for applications in many fields including the ratiometric thermometry based on thermal effect of fluorescence intensity ratio (FIR) of green fluorescence of Er3+, which is directly correlated with Judd-Ofelt parameters Ωi (i = 2, 4, 6). Present paper reports synthesis and Judd-Ofelt spectroscopic properties of Er3+-doped NaLa(WO4)2 µm-sized phosphor. The phosphor was synthesized by solid-state chemical reaction and characterized by X-ray diffraction and Raman scattering techniques. The results show that the phosphor is dominated by NaLa(WO4)2 crystalline phase and has a maximum phonon energy 927 cm−1. Judd-Ofelt analysis was done for the phosphor using a safe, reliable method based on diffuse reflection spectrum and Er3+ 1.5 μm fluorescence lifetime. First, diffuse reflection spectrum of the phosphor was measured and relative absorption spectrum was calibrated from it using Kubelka-Munk theory. Second, Er3+ 1.5 μm fluorescence lifetime of the phosphor was measured and absorption cross-section spectrum was obtained based on the assumption that the 1.5 μm emission has 100% quantum efficiency. Finally, based on the absorption cross-section spectrum, standard Judd-Ofelt analysis was carried out to extract the Ωi. Radiative rate, fluorescent branch ratio and radiative lifetime of some transitions have been obtained from the known Ωi values. In addition, FIR proportional factor was evaluated in terms of Ωi and compared with those values of other materials. The result shows that the phosphor has a better prospect for the application in ratiometric thermometry.