Tunable and white photoluminescence from Tb³⁺-Eu³⁺ activated Ca_0.3Sr_0.7Al₂O₄ phosphors and analysis of chemical states by X-ray photoelectron spectroscopy

Tb³⁺ and Eu³⁺ activated Ca_0.3Sr _0.7Al₂O₄ phosphors with tunable emissions were synthesized via urea assisted combustion method. The phosphors were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and photoluminescence (PL) spectroscopy. The XRD pattern of the Ca_0.3Sr_0.7Al₂O ₄:Tb³⁺, Eu³⁺ powder showed was composed of a single phase associated with monoclinic SrAl₂O₄, suggesting that SrAl₂O₄ was the main structure in the Ca_0.3Sr_0.7Al₂O₄ mixed aluminate host and Ca²⁺ substituted the Sr²⁺ ions. Consistent with the three dimensional structure of SrAl₂O₄, the XPS data indicated that there were two different lattice sites occupied by Sr ²⁺ in the lattice and resultantly Ca²⁺ could also be found at two different lattice sites. Tunable and white PL was generated when the phosphors were optically excited at different wavelengths using a monochromatized xenon lamp. The white PL with the Commission International de L'Eclairage (CIE) coordinates (x = 0.343, y = 0.325) was a result of the combination of the red line emission from Eu³⁺ and the blue and green line emissions from Tb³⁺.