Synthesis, luminescence properties and electronic structure of Tb3+-doped Y4−xSiAlO8N:xTb3+ – a novel green phosphor with high thermal stability for white LEDs

Abstract

A series of novel green Y_4−xSiAlO₈N:xTb³⁺ phosphors have been prepared by a high temperature solid state reaction. The phase formation and structural properties were analyzed by X-ray powder diffraction. The XRD results and SEM images show that the Y³⁺ can be substituted by Tb³⁺ for the max content of x = 1.5 and the most suitable sintering temperature is about 1500 °C. The PLE spectra of Y_4−xSiAlO₈N:xTb³⁺ phosphors exhibit a wide excitation band ranging from 200 to 500 nm, which matches well with the characteristic emission of n-UV chips. Under excitation of 380 nm, the phosphor shows four intense emission bands with emission peaks at 488 nm, 543 nm, 585 nm and 624 nm, respectively. These emissions were attributed to the characteristic ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. The optimum doping concentration of Tb³⁺ was found to be x = 2.0 which indicated that the concentration quenching effect in the Y_4−xSiAlO₈N:xTb³⁺ phosphor is very weak. The critical distance for the Tb³⁺ ions calculated by the concentration quenching is 3.64 Å. The detailed nonradiative energy transfer mechanism between Tb³⁺ ions is confirmed to be via a dipole–dipole interaction by the fluorescence decay analysis. Furthermore, with the introduction of Tb³⁺ ions, the reflectance spectra shows an obvious increment of reflectance in the region of 200–250 nm, which is due to the variation of electronic structure in the conductance band derived from Y³⁺ ions. Finally, the excellent thermal stability of the phosphors was demonstrated by the temperature dependence of the PL spectra. Compared to the initial intensity at room temperature (293.0 K), the relative PL intensity maintains high value of 96.5% at 475.2 K. The detailed thermal quenching behavior has also been interpreted.