Experimental and theoretical studies of red emission enhancing mechanism in Al-doped CaMoO4:Eu phosphor

Abstract

In this work, a complete picture of the relationship between the structural and optical properties of Al-doped CaMoO4:Eu phosphor was investigated empirically and theoretically. A series of Al-doped CaMoO4:Eu phosphors were synthesized by solid-state reaction. X-ray diffraction analysis and Rietveld refinement confirmed the formation of a single-phase tetragonal CaMoO4. Under the excitation wavelength of 395 nm, the phosphors exhibited typical red emission bands of Eu3+ as a function of Al3+ doping contents and reached a maximum value at 0.1 mol % Al3+. In addition, the CaMoO4:0.05Eu, 0.1Al phosphor showed chromaticity coordinates (0.6406, 0.3370), which is close to the pure red color as standardized by the National Television System Committee. Significantly, the red emission intensity of Al-doped CaMoO4: 0.05Eu phosphor was 5-times higher than that of the undoped one. This enhancement was explained by Judd-Ofelt (JO) analysis, from which intensity parameters (Ωλ, λ = 2, 4) and radiative properties including branching ratios (βr), transition probability (A), radiative lifetime (τcal), and stimulated emission cross-section (σe) of the phosphor were derived. Judd-Ofelt analysis confirmed that Al3+ promotes the covalent character in the Eu–O bond and the asymmetry in the CaMoO4 crystalline structure. The CaMoO4: 0.05Eu, 0.1Al phosphor generates strong red emission and possesses high values of branching ratio (81.80%), emission cross-section (102.3×10−22 cm2) and quantum efficiency (48.44%) and is potential for low-cost WLED applications.