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

A series of novel phosphate-tungstate phosphors, K2Gd( 1-x)( PO4)( WO4): xDy(3+) ( 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 (KGd)-Gd-2( PO4)( WO4) phosphor could absorb wavelengths from the UV to the blue region, and emit blue (similar to 480 nm), yellow (similar to 570 nm) and red (similar to 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 degrees C), the emission intensity of the KGPW: 0.05Dy(3+) phosphor with 388 nm excitation still retained about 76.8% of its initial intensity at room temperature. In addition, the color purity of K2Gd0.995(PO4)(WO4): 0.005Dy(3+) 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): xDy(3+) phosphors may have potential to be candidates for white LEDs for lighting and optical display applications.