Observation of Stark splitting in micro upconversion photoluminescence spectra of polycrystalline Ln³⁺ doped Y₂O₃ microspheres

Abstract

In this study, Yb3+-Er3+-Tm3+ doped Y2O3 microspheres were synthesized using the solvothermal method. Structural, morphological, and elemental analysis was done using XRD, FESEM, and EDX characterization techniques. The optical properties of the samples were determined using UV-Vis-NIR and upconversion photoluminescence measurements. The anti-Stokes emission peaks from these polycrystalline phosphor microspheres were obtained using a commercial micro-photoluminescence setup equipped with a 976 nm laser as an excitation source at room temperature. It was compared with that of a 2-3 mm spot size of 976 nm laser irradiation on the same sample. The micro-emission spectra were analyzed based on possible Stark splitting energy level transitions between the 2S+1LJ manifolds of Er3+ and Tm3+ ions. A detailed mechanism is outlined for emission in the entire visible region under 976 nm laser excitation.