Series of alkali metal ion co-doped with Eu3+ activated GdPO4 phosphors were synthesized by the conventional solid state method. Structural parameters were confirmed by the X-ray Rietveld refinement method. All the compounds are crystallized in the monazite phase with space group (P121/n1, No.14). Morphology and functional group analysis were performed on scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Room temperature photoluminescence (PL) spectroscopic results reveal that, on Eu3+ ion doping in the GdPO4 host matrix, the magnetic dipole transition (5D0 → 7F1) at 581 nm responsible for orange light, dominates the red emission with respect to the electric dipole transition (5D0 → 7F2) at 620 nm. It was found that the emission intensity increased up to 9 mol% of Eu3+ and then quenched due to multipolar interactions. Further, co-doping with Li+, Na+ and K+ ion in to Eu3+ activated GdPO4 phosphor led to an enhancement in luminescence intensity by reducing the parity restriction of electric dipole transitions as a consequence of suitable local distortion of the crystal field surrounding the Eu3+ activator ion. The results of Judd–Ofelt theory and radiative parameters suggest that these phosphors have a short lifetime, good quantum efficiency, excellent color purity compared to other reported Eu3+ doped phosphors. These results illustrate the mechanistic effect of alkali metal ions doping on luminescent properties of rare earth ion doped GdPO4 phosphors and help in optimization of their luminescent properties according to the practical requirements in optoelectronic and biomedical applications.< Réduire