Effect of Rare-Earth Doping on Upconversion Luminescence of CaF2 Glass–Ceramic Nanoparticles

In the current research work, an attempt has been made to study the upconversion properties of rare-earth doped CaF2 glass–ceramics. Er3+-Yb3+ doped CaF2 glass–ceramic nanoparticles are synthesized by sol–gel technique. CaF2 has been chosen as a low phonon host in the present work, and silica has been chosen as an oxide matrix. The amount of Ytterbium (Yb3+) has also been varied to observe the effect of concentration on both glass transition temperature and luminescence properties. The differential thermal analysis (DTA) graphs showed the initiation of crystallization temperature of CaF2 crystal and its behaviour with respect to higher Yb3+ concentration. Nanoparticles formed in the glassy matrix are approximately in the range of 10–25 nm and are validated by microstructural analysis. The X-ray diffraction (XRD) analysis was also performed on the prepared glass–ceramic and the crystallite size was calculated. The lattice parameter value calculated for the samples is ~5.78 Aº, which is higher than the standard cubic CaF2 crystal (5.4 Aº). A higher amount (mol %) of Yb3+ doping into the fluorite system has impacted the size, shape, and inter-planner distance of CaF2 nanocrystals. These nanoparticles are capable of offering multicolour up-conversion luminescence under near-infrared excitation of 980 nm. The colours recorded during the up-conversion process are green (525 nm) and red (626 nm), respectively.