Enhancement of broad-spectrum orange emission and thermal stability in Rb2-xCsxCaP2O7:0.015Eu2+ phosphors by improving local structural symmetry

The tunable 5 d-4f luminescence of Eu2+ is of great application value, but it is still full of challenges in terms of luminescence efficiency, thermal stability and precise tuning of luminescence colors. In this work, we synthesized a series of Rb2-xCsxCaP2O7:0.015Eu2+ phosphors based on the equivalent substitution strategy, allowing a certain proportion of Cs+ to replace Rb+ sites. By optimizing the Rb/Cs ratio, the structural symmetry of the [CaO6] octahedra can be enhanced, providing a high-stability and high-symmetry localized crystal field environment for the high efficiency luminescence of Eu2+. The experimental results confirmed that the broad-spectrum orange light emission could be achieved in Rb0·5Cs1·5CaP2O7:0.015Eu2+, and the integrated luminescence intensity was 6.9 times higher than that of Rb2CaP2O7:0.015Eu2+. Moreover, the luminescence intensity at 150 °C reached 93.3% of its room-temperature value. Using the synthesized phosphor as orange component, a white LED was assembled and a high-quality white light emission with Ra = 87.8 was achieved. These results suggest that rationally tuning the local structural symmetry around Eu2+ is an effective strategy to develop high-performance Eu2+-activated phosphors.