Rare earth doped sodium aluminium silicate for optical cooling application

Abstract

In the present research we successfully synthesized NaAlSiO2 crystals and doped (co- doped) them with various concentrations of Er3+, and Yb3+ ions via a hydrothermal method to unveil their up-conversion absorption bands in the visible region under 980 nm tuned laser pumping. The hydrothermal process was preceded by a hydro-gel preparation step and finally by an incipient wetness impregnation for successful doping. X-ray diffraction analysis revealed that crystallite size ranged between 14.5 nm to 37.4 nm. Moreover, elemental analyses performed on the prepared samples via scanning electron microscope (SEM) equipped with Energy Dispersive X-ray Spectrometer (EDS) unraveled even distribution of both ions. In addition, FTIR analysis demonstrated the presence of absorbed OH group in the host materials which were removed via optimized annealing of the sample. To elucidate absorption behavior of the as-synthesized host material, UV-Vis-NIR spectroscopy was used and resulted in absorption bands at 487 nm, 521 nm, 540 nm, 651 nm and 971 nm, respectively. On the other hand, emission properties were investigated by means of Photoluminescence (PL) spectroscopy. PL analysis revealed emission lines in the visible range of spectrum at 521 nm, 540 nm and 651 nm. Optimizing annealing temperature proved critical in enhancing up-conversion emission, Power dependence analysis showed increased emission with increasing pumping power. Finally, temperature dependency tests showed the crystals to be promising materials for up-conversion laser optical cooling application at temperature ranging from 50 to 400 °C.