Chemical bond parameters, charge transfer band, tunable white light of Tm3+and Sm3+ coactivated Ca9Gd(VO4)7

Abstract

The dependence of photoluminescence properties of Sm3+ or/and Tm3+ codoped Ca9Gd(VO4)7 (CGVO) samples on the crystal structure was discussed quantitatively and qualitatively. Tm3+ and Sm3+ co-doped CGVO phosphors show blue and orange dual emission bands under the UV excitation. The photoluminescence intensity ratio of blue and orange emission could be tuned by adjusting the concentration of Tm3+ and Sm3+ ions and as a result the emission color varies from blue to white to orange. Based on the dielectric theory of complex crystal, the important parameters of the chemical bonds such as the covalency and the polarizability of the chemical bond volume of O–V or O–Ca were calculated quantitatively. It was quantitatively demonstrated that the broad excitation spectrum was not the O–Sm charge transfer (CT), but is the O–V CT. Also quantitative calculation indicated that the broad excitation band with the peak at around 325nm was assigned to O–V3 CT energy, which can efficiently be transferred to the activator probably due to the strong covalency of V3–O8 bond (0.3784) and V3–O10 bond (0.3854) in the V–O–Sm/Tm bond.