Dy³⁺ doped thermally stable garnet-based phosphors: Luminescence improvement by changing the host-lattice composition and co-doping Bi³⁺

A series of (Gd_1-xY_x)_2.94-yAl₅O₁₂: 0.06Dy³⁺,yBi³⁺(x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, y = 0.000, 0.015, 0.030, 0.045, 0.060) phosphors has been prepared by a sol-gel combustion method. X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), diffuse reflection, fluorescence decay curves, temperature-dependent photoluminescence and CIE color coordinates were used to characterize the prepared phosphors. The emission intensity of Dy³⁺ was greatly improved by co-doping the sensitizer of Bi³⁺ ions and changing the composition of the matrix via replacing gadolinium with Y³⁺ ions. The influence of different Y³⁺ and Bi³⁺ concentrations on the properties of the phosphor were discussed. The optimized composition was determined to be (Gd_0.2Y_0.8)_2.835Al₅O₁₂: 0.06Dy³⁺,0.045Bi³⁺. Its intensity is almost double the intensity in YAG: Dy³⁺,Bi³⁺, four times stronger than that of GAG: Dy³⁺,Bi³⁺ and 15 times stronger than that of YGAG: Dy³⁺. The band gap and decay curves of the phosphors were investigated to explore the relationship between the intensity and the content of Y³⁺. In addition, good thermal stability of (Gd_0.2Y_0.8)_2.835Al₅O₁₂: 0.06Dy³⁺,0.045Bi³⁺ was observed according to the temperature-dependent PL spectra. The enhanced luminescence intensity and good thermal stability of the phosphor are conducive to improved application in the field of white light-emitting diodes (W-LEDs).