Enhanced green upconversion emission in NaYF4:Er3+/Yb3+/Li+ phosphors for optical thermometry

Abstract

The NaYF4 phosphors codoped with Er3+-Yb3+ have been synthesized by hydrothermal method using oleic acid as a chelating agent. The crystal structure and surface morphology has been identified with the help of powder X-ray diffraction (PXRD) and field emission scanning microscopy (FE-SEM) technique, respectively. The presence of different functional groups in the developed phosphors have been analyzed by using the Fourier transform infrared spectroscopy (FTIR) technique. The optical non-linear behavior of the prepared phosphors has been performed by using the excitation at 980 nm from a CW diode laser. The effect of Li+ ions tri-doping on the structural and luminescence behavior of the Er3+-Yb3+ codoped NaYF4 phosphors has been discussed suitably. The effect of variation of pump power density on the UC emission intensity of different bands has been investigated. The optical temperature sensing behavior based on the green UC emissions of the Er3+-Yb3+-Li+ tri-doped NaYF4 phosphors under the excitation at very low pump power density (∼0.32 W/cm2) has been studied. The results obtained from the present study indicate that the Er3+-Yb3+-Li+ tri-doped NaYF4 phosphors may be of particular interest in developing the NIR to visible upconverters, green display devices and temperature sensors.