The structural characterizations of La₂O₃ phosphors doped/codoped with Tm³⁺ and Yb³⁺ ions synthesized by the urea assisted solution combustion technique were performed using X-ray diffraction analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. Codoping with Zn²⁺/Mg²⁺ ions causes an increase in the particle size and aggregation for the La₂O₃:Tm³⁺–Yb³⁺ phosphor. The upconversion (UC) study under 980 nm excitation shows four UC emission bands centred around 476 nm (¹G₄ → ³H₆), 653 nm (¹G₄ → ³F₄), 702 nm (³F₂ → ³H₆) and 795 nm (¹G₄ → ³H₅). The effect of codoping with Zn²⁺ and Mg²⁺ ions in the Tm³⁺–Yb³⁺ codoped La₂O₃ phosphor was investigated. Decay curve analysis of the prepared phosphors was done to understand the mechanism of the upconversion emission intensity variation due to codoping with Zn²⁺/Mg²⁺ ions. The purity of colour emitted from the sample does not show any change with variations in pump power density.