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 (O^2-) 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.