Effect of Eu3+ concentration on the structure and photoluminescence properties of the BaAl2O4/MgAl2O4/BaCO3:x% Eu3+ (0 ≤ x ≤ 1.5) mixed phases synthesized by citrate sol-gel method

Abstract

We report the structural, morphological and photoluminescence properties of BaAl 2 O 4 /MgAl 2 O 4 /BaCO 3 :x% Eu 3+ (0 ≤ x ≤ 1.5) mixed phases (hereafter called BMB:x% Eu 3+ ) synthesized by a citrate sol–gel method. X-ray diffraction confirms the coexistence of hexagonal BaAl 2 O 4 , cubic MgAl 2 O 4 and orthorhombic BaCO 3 phases; indexed XRD patterns are presented. Scanning and transmission electron microscopy show an Eu 3+ -dependent morphological evolution from nanorods to irregular crystallites. Photoluminescence spectra (λ ex = 226 and 268 nm) reveal defect-related bands in the undoped BMB (centred at 550 nm) and sharp Eu 3+ 5 D 0 → 7 F J transitions in doped samples. The Eu 3+ -activated emission intensity at 620 nm is maximized at x = 1.1 % (optimal concentration), above which concentration quenching reduces intensity. Spectral deconvolution and lifetime reanalysis (bi-exponential fits) indicate energy transfer from host defect states to Eu 3+ and the involvement of at least two Eu 3+ environments. Colour coordinates shift from green to orange-red with increasing Eu 3+ concentration. These findings identify composition and morphology conditions for optimized orange-red emission in the BaAl 2 O 4 /MgAl 2 O 4 /BaCO 3 mixed-phase phosphors.