Selective reduction of visible upconversion emissions induced by Bi3+ in Tm3+/Yb3+-doped Y0.89-xBixVO4 microcrystals

In this article we have shown that the intensity ratio of near infrared (NIR) to blue upconversion emission from Tm3+ ions can be enhanced up to 800 times by simple control of the concentrations of Bi3+/Y3+ in Tm3+(0.01)/Yb3+(0.10)-doped Y0.89-xBixVO4 (x = 0 to 0.89) microcrystals. The intensity of the strong blue emission occurring near 475 nm due to the (1)G(4)-> H-3(6) transition is selectively reduced upon bismuth doping, while the intensity of the NIR emission at 800 nm (H-3(4)-> H-3(6)) is hardly affected. The enhanced NIR/blue emission intensity achieved via the upconversion process is advantageous in reducing the background scattering, and consequently increases the contrast in the bio-imaging applications. Several control experiments were performed to unravel the role of Bi3+ ions in the reduction of the blue emission intensity. An energy transfer mechanism involving Tm3+, Bi3+ and Yb3+ ions is proposed for the preferential reduction in intensity of the blue emission. All microcrystal samples were completely characterized using XRD, Raman and photoluminescence methods.