Wide range color tunability and efficient energy transfer of novel NaCaGd(WO4)3:Tb3+,Eu3+ phosphors with excellent thermal stability for pc-WLEDs

Abstract

A sequence of NaCaGd(WO₄)₃:Tb³⁺,Eu³⁺ phosphors were prepared via a high temperature solid state reaction method. XRD, Rietveld refinement and SEM were carried out to identify the crystalline phase and morphology. The photoluminescence properties of as-synthesized phosphors excited by ultraviolet light were studied in detail. According to the photoluminescence emission spectra and fluorescence decay curves, efficient energy transfer occurred in these Tb³⁺, Eu³⁺ co-doped NaCaGd(WO₄)₃ phosphors. The energy transfer efficiency reached up to 92.267% when the doping concentration of Eu³⁺ ions reached 0.4 mol, and the dominant energy transfer mechanism was determined to be the dipole–dipole interaction. The color tunability can be realized from green to red by adjusting the Tb³⁺/Eu³⁺ doping ratio. Moreover, the representative NaCaGd(WO₄)₃:0.6Tb³⁺,0.1Eu³⁺ sample exhibited excellent thermal stability, and their emission intensity at 423 K still maintains about 84.7% of that at an initial temperature of 303 K. Ultimately, the as-packaged white LED device exhibited an outstanding correlated color temperature (CCT) of 4505 K and a color rendering index (R_a) of 87.3. The results mentioned above show that all the obtained phosphors are promising candidates in the fields of display devices and pc-WLEDs.