Luminescence of Tm3+, Yb3+ Co-doped CaLaAlO4/LaAlO3 Mixed Phase Phosphor for Solid-state Lighting Application

Abstract

CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ upconversion phosphors were prepared via the combustion method. The Tm3+ dopant concentration was constant (Tm=0.5mol%), while the concentration of Yb3+ co-dopant was varied (Yb = 1 – 10 mol%). The X-ray diffraction studies indicated a mixture of phases (tetragonal and hexagonal of CaLaAlO4 and LaAlO3 respectively). The optical absorption spectra of the upconversion phosphors have two absorption bands centered at 253 nm, and another band at 440 nm. The band at 253 nm is ascribed to the charge transfer band (CTB) between the ligand (O2-) and Yb3+ ions, while the broad band located at 440 nm was related to defect states in the lattice. The energy bandgap and refractive index of the optimized phosphor were 4.73 eV and 1.76 respectively. The upconversion emission peaks centered at 478 nm (1G4 → 3H6), 654 nm (1G4 → 3F4), and 801 nm (3H4 → 3H6) are associated to the electronic transitions of Tm3+ ions. As the Yb concentration increases, the colour emission is tuned from bluish white to blue light. The CCT and CIE coordinate of (0.2419, 0.2463) showed that the phosphor doped with 10 mol% of Yb3+ produces a bluish-white and its colour purity was 80%. Thus, the strong bluish-white light emission produced by the CaLaAlO4/LaAlO3: 0.5%Tm3+, xYb3+ phosphors could be used for solid-state lighting (SSL) or in multicolour displays.