Effect of transition metal ion (Nb⁵⁺) doping on the luminescence properties of self-activated Ca₂AgZn₂V₃O₁₂phosphors

Ca₂AgZn₂V₃O₁₂self-activated vanadate phosphors were synthesized via a citrate assisted sol-gel method. The phase formation of the garnet structure was verified by X-ray diffraction (XRD) and Rietveld refinement analyses. From XRD patters, it is clear that the prepared samples were crystallized in cubic phase with a space group Ia3¯ d (230). The photoluminescence excitation spectrum showed a broad band in the UV region and a broad emission spectrum was observed in the wavelength range of 400–750 nm. The doping of transition metal ion (Nb⁵⁺) in the vanadium site changed the luminescence properties. Doping of Nb⁵⁺ions increased the V[sbnd]O bond length from 1.7016 to 1.7148 Å which causes the increase in luminescence intensity and the red shift of emission spectrum. The increase in the luminescence intensity may also be attributed to the emission from Nb⁵⁺ions. The thermal stability of the materials was measured and the activation energy was found to be 0.254 eV. The luminescence decay time was also measured and the values were found to be 158 and 154 μs for undoped and doped samples, respectively. The prepared phosphors exhibited a greenish yellow emission under UV excitation, indicating that they can be potential candidates for the application in UV-based WLEDs.