Multi-wavelength excited white-emitting K2Gd(1−x)(PO4)(WO4):xDy3+ phosphors with satisfactory thermal properties for UV-LEDs

Abstract

A series of novel phosphate–tungstate phosphors, K₂Gd_(1−x)(PO₄)(WO₄):xDy³⁺ (0 ≤ x ≤ 0.07), were synthesized successfully via a conventional solid-state reaction method for the first time. XRD, GSAS Rietveld refinement, FT-IR, Raman, diffuse reflectance spectra, luminescent spectra, and thermal quenching were applied to investigate the phase, structure, luminescence and thermal stability properties. The results showed that the Dy³⁺-activated K₂Gd(PO₄)(WO₄) phosphor could absorb wavelengths from the UV to the blue region, and emit blue (∼480 nm), yellow (∼570 nm) and red (∼650 nm) light from the f–f transitions of Dy³⁺ ions. The dominant energy transfer mechanism for Dy³⁺ ions was dipole–dipole interaction. An analysis of the thermal quenching indicated that the obtained phosphors have excellent thermal stability. As the temperature increased to 423 K (150 °C), the emission intensity of the KGPW:0.05Dy³⁺ phosphor with 388 nm excitation still retained about 76.8% of its initial intensity at room temperature. In addition, the color purity of K₂Gd_0.995(PO₄)(WO₄):0.005Dy³⁺ was calculated to be 90% with a correlated color temperature of 5569 K. Therefore, these results suggest that multi-wavelength excited K₂Gd_(1−x)(PO₄)(WO₄):xDy³⁺ phosphors may have potential to be candidates for white LEDs for lighting and optical display applications.