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Trivalent ytterbium and erbium doped in yttrium oxysulfide (Y₂O₂S:Yb³⁺,Er³⁺) phosphors were synthesized by solid state flux fusion method and their upconversion spectral properties were studied as a function of different Yb³⁺ concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles with an average size of 3.8μm. The detailed optical characterizations such as absorption, emission, and fluorescence decay were performed to explore the emission processes in the UV–VIS–NIR as well as to quantitatively estimate the fluorescence quantum yield. Upconversion spectral studies show that for all the compositions, green emissions are stronger; in particular the green emission intensity is 1.7 times stronger than the red intensity with composition of 9mol% Yb³⁺ and 1mol% Er³⁺. Mechanisms of upconversion by two-photon and energy transfer processes are interpreted …