Controlling the final phase of multiphase KGdF4 materials via chemical synthesis and structural phase transition

Abstract

This study proposes a method for the final phase control of KGdF 4 crystals for the first time, based on a chemical synthesis and structural phase transition process with increased temperature. X-ray diffraction and high-resolution transmission electron microscopy were employed to characterize the resulting structures and reveal phase transition trends. Subsequently, a theoretical phase transition model was constructed. This model indicated that final products are obtained through a combination of chemical synthesis and structural phase transition. Furthermore, it was observed that the chemical synthesis process dominates the low-temperature region, whereas the structural phase transition process dominates the high-energy region because of the additional extra energy. Finally, the density of states was theoretically calculated using the firstprinciple theory, shedding light on the structural phase transition process. This study, therefore, provides a potentially controllable method for the synthesis of desired KGdF 4 crystal phases.

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications

“…The partial phase transformation can be attributed to the change in pH during the preparation of the sol, from pH 7 of NP suspension to pH 2 of the final sol. Some authors reported that the nanoparticles with the formula NaLnF 4 (Ln = Gd, Y, Li) are very sensitive to pH changes [46,50]. Figure 4a shows the FTIR spectra obtained for undoped and 1.5Eu 3+ -doped NaGdF4 nanoparticles heat-treated at 450 °C for 5 h (violet and blue line, respectively) and 80SiO2-20(1.5 Eu 3+ : NaGdF4) heat-treated at 450 °C for 5 h and dried at 75 °C overnight (red and green line, respectively) in the range of 4000 cm −1 to 400 cm −1 .…”