NaZnPO₄:Er³⁺/Tm³⁺/Yb³⁺/Li⁺ phosphors successfully synthesized by conventional solid state reaction method have been characterized through XRD, FESEM, EDAX, diffuse reflectance spectra and FTIR analysis. Downconversion (DC) and upconversion (UC) emission study of the developed phosphors have been carried out and the dynamics involved in the UC emission mechanism discussed. UC based near white light emission, intrinsic optical bistability and temperature-dependent population re-distribution ability have been reported. The UC emission intensities of the blue, green and red bands are enhanced about ∼333, ∼86 and ∼2 times, respectively, on codoping with Yb³⁺ ions, whereas the green and red UC emission bands are enhanced by ∼130 and ∼7 times, respectively, on codoping with Li⁺ ions as compared to that of the Er³⁺–Tm³⁺ co-doped phosphors. Photometric characterization confirms the near white light emission from the developed phosphors. The nature of interaction for the concentration quenching is found to be dipole–dipole type. Time independent intensity ratios arising from the Er³⁺ ions are observed which shows that the developed materials can be used in making thermally stable phosphors.