Upconversion and downshifting emissions of Ho3+-Yb3+ co-doped ATiO3 perovskite phosphors with temperature sensing properties in Ho3+-Yb3+ co-doped BaTiO3 phosphor

Abstract

In this work, we report a comparative study on upconversion and downshifting properties of Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors for the first time. The phosphor samples are prepared via solid state reaction method in a programmable furnace at 1523 K. The phosphor samples are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The EDS analyses show the presence of the desired elements used in the synthesis. The vibrational structures of the phosphor samples are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to Ho3+ and Yb3+ ions. The optical band gap (Eg) is calculated using Wood and Tauc relation and its values are found to be 3.61, 3.20 and 3.32 eV for the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphor samples, respectively. The upconversion emission spectra are monitored by exciting these phosphor samples at 980 nm. The phosphor samples give intense green emission in all the cases. However, the UC emission intensity is higher for the Ho3+-Yb3+ co-doped CaTiO3 perovskite phosphor. These phosphor samples also give intense green downshifting emission upon 419 and 452 nm excitations. The Ho3+-Yb3+ co-doped BaTiO3 perovskite produces relatively larger emission intensity among these phosphors. The lifetime of green emitting level (5F4) of Ho3+ ion shows temporal behavior of these perovskite phosphors. Furthermore, the temperature versus UC emission intensities of the green thermally coupled levels of Ho3+-Yb3+ co-doped BaTiO3 phosphor gives the fluorescence intensity ratio (FIR) and FIR-based relative (SR) and absolute (SA) temperature sensor sensitivities are obtained as 0.0034 K-1 and 0.0050 K-1, respectively at 305 K. Thus, the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors may be found suitable in display devices, solid state lighting, upconversion based devices and temperature sensing devices.