Site-selective occupation of Eu2+ activators toward full-visible-spectrum emission in well-designed borophosphate phosphors

Abstract

Efficient modulation of the site-selection of activators is of great significance for designing high-performance phosphors. Herein, we report that site-selective occupation of Eu2+ activators in mixed anion-group realizes full visible spectrum emission in borophosphate K2BaCa(PO4)2−x(BO3)x:0.03Eu2+ phosphors, which are designed by using K2BaCa(PO4)2:0.03Eu2+ cyan-emitting phosphor. In the pristine sample, there are four crystallographic sites (Ca, Ba, K1 and K2), yet, Eu2+ ions only occupy the K1 and K2 sites. By anion-group cosubstituting (PO4)3− with (BO3)3− units, the most strikingly discoveries here are that a Eu2+-substitution new pathway is opened up, rendering partial Eu2+ ions enter Ca crystallographic site that could never be occupied before, yielding an intense Eu2+ red emission band at 660 nm, and consequently realizing spectral tuning from original cyan-emitting to white-light emission. The structural analysis and DFT calculations support the concept that Eu2+ ion preferably occupy the Ca site, and revealing impressive insights of site-selective occupation of Eu2+ in the borophosphate white-light phosphors. Importantly, using only this full-visible-spectrum phosphor (x = 0.4), as-prepared WLED shows excellent color quality (Ra = 90.4 and R9 = 93.8). This work not only presents an in-depth investigation of site-selection of Eu2+, but also opens a new way to design full-visible-spectrum phosphors.