*2.2. Characterizations*

The crystal structure of the optimized Mn4+activated CaSb2O6 (CSO: 2Mn4+) phosphor sample was analyzed by X-ray diffraction (XRD) (Mac Science, M18XHF-SRA, Yokohama, Japan) with Cu kα (λ = 1.5406 Å). The morphology of the CSO: 2Mn4+ phosphor sample was studied using a field-emission scanning electron microscope (FE-SEM) (ZEISS, LEO SUPRA 55, Oberkochen, Baden-Württemberg, Germany). The elemental analysis was performed using an energy dispersive X-ray (EDX) spectrometer attached with FE-SEM. The oxidation states of the elements were found using X-ray Photoelectron spectroscopy (XPS) (K-alpha, Thermo electron, Gangnam-gu, Seoul, Republic of Korea). The photoluminescence excitation (PLE) and PL emission (PL) properties were investigated using a Sinco FluoroMate FS-2 spectrofluorometer, Gwangju, Korea. The lifetime was measured on

a Photon Technology International (PTI) fluorimeter, Kyoto, Japan, which was equipped with a phosphorimeter attachment to the main system along with a 25 watt Xe-flash lamp.
