Structural, optical and temperature dependent photoluminescence properties of Cr3+-activated LaGaO3 persistent phosphor for optical thermometry

Cr3+ doped LaGaO3 phosphor was prepared by hydrothermal reaction method with post-annealing treatment. XRD pattern showed the pure orthorhombic phase of LaGaO3 at an annealing temperature of 1000 °C. TEM image showed the particles in the range 40-120 nm. The bandgap energy and Urbach tail increased in the doped sample as compared to the undoped sample as estimated from UV–visible diffuse reflectance spectra. PL excitation spectra showed peaks in UV, blue and orange regions. The emission spectra showed broadband with peaks in the NIR region due to emission from 4T2 and 2E states. The intermediate strength of the crystal field has been calculated from the estimated spectroscopic parameter. The average lifetime was found to be in the ms range. Afterglow decay was also recorded. From the low-temperature PL, the zero phonon line, stokes shift energy, vibrational energy and Huang-Rhys parameter were calculated. With rising the temperature, PL emission peak intensity and lifetime values decreased and FWHM increased because of increased numbers of electrons in 4T2 state and increasing non-radiative transition. Temperature-dependent peak intensity ratios and lifetime values were utilized for temperature sensing applications in below room temperature and above room temperature. The results indicate the possibility of present phosphor to be used as optical nanothermometer.