Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

Ca₃(PO₄)₂:1mol%Ce³⁺/xGd³⁺ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce³⁺ ions centered at ~265 nm. The PL emission properties of the Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphors were studied as a function of the Gd³⁺ ion concentration. The Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd³⁺ ion. The CIE chromaticity diagram of Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.