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

Abstract

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 Y_0.89−xBi_xVO₄ (x = 0 to 0.89) microcrystals. The intensity of the strong blue emission occurring near 475 nm due to the ¹G₄→³H₆ transition is selectively reduced upon bismuth doping, while the intensity of the NIR emission at 800 nm (³H₄→³H₆) 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.