Great improvement in intensity and thermal stability of Ca9Ga(XO4)7: Cr3+ near-infrared photoluminescence by next nearest coordination substitution

Broad band near-infrared emitting phosphors activated with Cr 3+ ions have great potential in a variety of applications. The luminescence efficiency and thermal stability are two critical parameters that are highly concerned in practical applications. In this work, a series of Cr 3+ ion-activated Ca 9 Ga(PO 4 ) x (VO 4 ) 7-x were synthesized. The photoluminescence (PL) properties of Cr 3+ were studied as functions of coordination environment, Cr 3+ concentration and temperature. The coordination environment of Cr 3+ ions is modified by gradually substitution of P by V without change the crystal structure of the host lattice. A continuous solid solution is formed, and the cell parameters and volume increase monotonically with V content. Great improvement in the intensity is observed for Ca 9 Ga(PO 4 ) 3.5 (VO 4 ) 3.5 , which increases by 26 and 2.4 times than the parents compositions Ca 9 Ga(PO 4 ) 7 and Ca 9 Ga(VO 4 ) 7 , respectively. Decay dynamic analysis suggests that both coordination environment modification and reduction of quenching center responsible for the great enhancement. An optimized concentration of 3.0 % is revealed and the intensity at 433 K maintains 81.1 % of the intensity at 293 K, respectively.