Luminescence optimization with superior asymmetric ratio (red/orange) and color purity of MBO3:Eu3+@SiO2 (M = Y, Gd and Al) nano down-conversion phosphors

Y1-xBO3: Eu-x(3+) (0.07 <= x <= 0.5 moles) and Y0.7-2x (Gd-x, Al-x) BO3:Eu-0.3(3+) (0.05 <= x <= 0.3 moles) powder phosphors have been synthesized by a novel co-precipitation technique followed by heat treatment. Luminescence optimization was carried out by optimizing the dopant Eu3+ concentration, substitution of Y3+ with Gd3+/Al3+ and finally with SiO2 shell coating. The inversion symmetry of Eu3+ ions were lowered with Eu3+ concentration and substitution of Y3+ with Gd3+/Al3+, respectively. It has been noted that the intensity behavior of PL peaks of Eu3+:5D(0)-> F-7(1), D-5(0)-> F-7(2) are not only sensitive to the inversion symmetry of Eu3+ ions, but also to the monitoring excitation wavelengths. Due to nanosize particle distribution, the optimum activator (Eu3+) concentration (30 mol%) was found to be extremely at higher level, compared to the bulk phosphors. The asymmetric ratio (red/orange) and color purity of the optimized phosphors, Y0.7BO3:Eu-0.3(3+) (with crystallite size, D = 32 nm) and Y0.3Gd0.2Al0.2BO3:Eu3+ (D = 17 nm) were further enhanced with an SiO2 coating. Based on the systematic study, the nanophosphor Y0.7BO3:Eu-0.3(3+)@SiO2 with an R/O ratio as 6.710 and color coordinates (x = 0.6612, y = 0.3357) is optimized as a remarkable phosphor having superior features than the commercial, available literature data results.