Observation of Stark splitting in micro upconversion photoluminescence spectra of polycrystalline Ln 3+  doped Y 2 O 3 microspheres.

In this study, Yb 3+ -Er 3+ -Tm 3+ doped Y 2 O 3 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 spectroscopy 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 the emission spectra taken from 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+1 L J manifolds of Er 3+ and Tm 3+ ions. A detailed mechanism is outlined for emission in the entire visible region under 976 nm laser excitation.