Improved thermal stability of luminescence by anion modification in Na2Y(MoO4)(PO4):Tb3+,Eu3+ red-emitting phosphors

Polyhedral anions have been used as supporting host structure to improve the luminescent properties of phosphors. However, the underlying mechanism for improving the thermal stability of luminescence by anion modification is rarely studied. In this paper, it was reported for the first time that thermal quenching and luminescent properties of red-emitting phosphors, Na2-nY(MoO4)1+n(PO4)1-n:Tb3+,Eu3+, can be adjusted by the ratio of acid radicals. Rietveld refinements and Debye temperature calculations show that the subtle replacement of [MoO4]2– by [PO4]3– results in the shrinkage of the crystal lattice and an improvement in lattice rigidity of the host, but does not change the crystal type. A detailed explanation of the mechanism for adjustable thermal stability of luminescence is provided via temperature-dependent X-ray diffraction, Raman, formation energy, and work function. The strategy of anion modification reveals an effective method for improving the thermal stability and tuning the luminescent spectra of phosphors, it also sheds light on the development of new phosphors. Furthermore, Na1.4Tb0.5(MoO4)1.6(PO4)0.4:0.5Eu3+ red-emitting phosphor with an internal quantum efficiency of 66.67% can be efficiently excited with blue light (465 nm) and the integrated intensity at 425 K is 86.4% of that at 300 K. The controllable local structure-dependent luminescence makes this novel red-emitting phosphor attractive for both blue and near-UV chips based WLEDs.