EN
CaAl₂O₄:Eu³⁺ (1 mol.%) co-doped with varying concentration of Gd³⁺ (1, 2, 5, and 10 mol.%) were prepared by combustion synthesis method at 600°C and further annealed at 1000°C. All the compositions were investigated for their structural and photoluminescence properties. It was observed that both states of europium i.e. Eu³⁺ and Eu²⁺ were present and ratio of these states changes on heating at 1000°C. The materials synthesized at 600°C showed high intense peak around 440 nm due to presence of Eu²⁺ and less intense peaks in the red region which were due to presence of Eu³⁺. On annealing the compounds at 1000°C, intensity of peak around 440 nm decreases and intensity of peaks in the red region increases significantly. The ⁵D₀ → ⁷F₃ transition due to Eu³⁺ at 657 nm appears as the highest intensity peak. All co-doped samples annealed at 1000°C showed the higher intensity than the mono doped sample which is due to energy transfer from the Gd³⁺ to Eu³⁺. The second rare-earth ion (Gd³⁺) acts as sensitizer and enhances the photoluminescence intensity. The X-ray diffraction spectra reveal the monoclinic phase of CaAl₂O₄ in all the samples which showed that Eu³⁺ and Gd³⁺ do not change the crystalline structure of calcium aluminate.