Enhanced quantum efficiency and thermal stability in CaWO4:Eu3+ phosphor based on structural modification induced by co-doping Al3+

Abstract

The thermally stable phosphors with excellent luminous properties are of great significance for their practical applications in the white light emitting diodes (wLEDs). Herein, a variety of CaWO4:xEu3+, yAl3+ (0 ≤ x ≤ 0.24; 0 ≤ y ≤ 0.10) red phosphors could be efficiently pumped by near-UV LED chips were successfully fabricated through the solid-state method. The phase composition, microstructure, luminescent behaviors, quantum efficiency as well as thermal stability are fully studied. For the CaWO4:Eu3+, Al3+ system, it is confirmed that the change of [Ca/Eu/Al-O] polyhedral volume caused by cation-size mismatch is not a decisive factor for the change in the overall unit cell volume, and the additional [W-O] tetrahedral volume changes should also be considered. Moreover, it is also found that, as the co-doping of Al3+, the polyhedron distortion resulting from the cation-size mismatch and the induced oxygen deficiency causes the loss of local symmetry around Eu3+, resulting in the improved chromaticity feature and the excellent luminescence properties. Impressively, the prepared CaWO4:0.20Eu3+, 0.08Al3+ phosphor possesses a higher quantum efficiency of 84.2% and a superior thermal stability retaining 83% at 423 K with respect to that at room temperature. These results show that the CaWO4:0.20Eu3+, 0.08Al3+ red phosphor can be served as an excellent candidate for wLEDs.