Study of near-infrared induced color tunability and optical bistability in Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor

Abstract

This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.