Generation of color tunable emissions from Ho3+/Tm3+/Yb3+ co-doped YTaO4 phosphors through NIR excitation under different conditions (variation of concentration, excitation pump power and the external temperature)

•The color tunability from green to blue region by varying the concentration of sensitizer (Yb3+ ion).•The color tunability on variation with pump power of 980 nm excitation source.•At higher pump power, the high concentration of Yb3+ produces highly intense broad-band whitish UC emission.•External temperature dependent color tunability has also been observed and verified by color coordinates in CIE diagram. [Display omitted] This work reports the color tunable emission from Ho3+/Tm3+/Yb3+ co-doped YTaO4 phosphors synthesized through high temperature solid state reaction method. Pure phase formation and the effect of concentrations of dopants on the phase have been confirmed by X-ray diffraction (XRD) measurements. Vibrational structure and the phonon frequencies have been monitored using Fourier transform infrared (FTIR) measurements. The color tunability from green to blue regions has been studied by varying the concentration of sensitizer (Yb3+ ion) via upconversion (UC) process on excitation with 980 nm diode laser qualitatively as well as quantitatively. The variation in UC emission intensity in different regions at different concentrations of Yb3+ ion is explained using energy level diagram of Ho3+, Tm3+ and Yb3+ ions. The color tunability has been also observed with pump power of excitation source. The locus of the color coordinates in CIE diagram of the YTaO4:Tm3+, Ho3+, Yb3+ show different curvatures with different pump powers at different Yb3+ concentrations. The laser induced optical heating is responsible for variation in the color on increasing pump power. The color coordinates has been also investigated by varying the external temperature. The color tunable behaviours of YTaO4:Tm3+, Ho3+, Yb3+ phosphor by varying the concentration of Yb3+ ion, pump power of diode laser and at different external temperatures in the same material makes it suitable for the applications in security and fluorescence imaging.