Intense blue upconversion emission and intrinsic optical bistability in Tm3+/Yb3+/Zn2+tridoped YVO4phosphors

Monochromatic NIR UC emission in Tm3+/Yb3+co-doped GdVO4 phosphor: the effect of the Bi3+ ion concentration and pump power of a diode laser

A Tm³⁺/Yb³⁺/Bi³⁺ co-doped GdVO₄ phosphor sample has been synthesized using a high-temperature solid-state reaction technique. The X-ray diffraction patterns reveal pure phase formation and crystalline behavior of the synthesized samples. Intense blue and NIR upconversion emissions have been observed upon excitation with a 980 nm diode laser. It is found that the addition of the Bi³⁺ ion to the phosphor reduces the intensity of blue emission and enhances the NIR emission intensity to the extent that NIR emission is nearly monochromatic [(I_NIR/I_Blue) ∼ 14]. This ratio is further improved up to 70 times (almost monochromatic) by varying the pump power of the diode laser. Thus, this material can be used as a cheap source of monochromatic NIR emission at 800 nm for bioimaging.