Effects of Bi3+ on down-/up-conversion luminescence, temperature sensing and optical transition properties of Bi3+/Er3+ co-doped YNbO4 phosphors

A series of YNbO4:Bi3+ and YNbO4:Bi3+/Er3+ phosphors were prepared by a conventional high temperature solid-state reaction method. The results of XRD and Rietveld refinement confirm that monoclinic phase YNbO4 samples are achieved. The down-/up-conversion luminescence of Er3+ ions was investigated under the excitation of ultraviolet light (327 nm) and near infrared light (980 nm). Under 327 nm excitation, broad visible emission band from Bi3+ ions and characteristic green emission peaks from Er3+ ions are simultaneously observed, while only strong green emissions from Er3+ ions are detected upon excitation of 980 nm. Remarkable emission enhancement is observed in down-/up-conversion luminescence processes by introducing Bi3+ ions into Er3+-doped YNbO4 phosphors. Pumped current versus up-conversion emission intensity study shows that two-photon processes are responsible for both the green and the red up-conversion emissions of Er3+ ion. Through the study of the temperature sensing property of Er3+ ion, it is affirmed that the temperature sensitivity is sensitive to the doping concentration of Bi3+ ions. By comparing the experimental values of the radiative transition rate ratio of the two green emission levels of Er3+ ions and the theoretical values calculated by Judd-Ofelt (J-O) theory, it is concluded that the temperature sensing property of Er3+ ions is greatly affected by the energy level splitting. (C) 2021 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.

Automated summary

YNbO4:Bi3+ and YNbO4:Bi3+/Er3+ phosphors were prepared and their luminescence properties and temperature sensing performance were investigated. It was found that the introduction of Bi3+ ions can remarkably enhance the down-/up-conversion luminescence of Er3+ ions, and the temperature sensitivity is affected by the doping concentration of Bi3+ ions.