Growth of KAlF₄ and Na₅Al₃F₁₄ Aluminum Fluoride Single Crystals by Bridgman Method

Abstract

Highly transparent KAlF4 and Na5Al3F14 fluoride bulk single crystals in size of ≈Ф 50 mm × 10 mm are successfully grown for the first time by a modified Bridgman method. The physicochemical properties of the single crystals are investigated with the help of X‐ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG‐DTA), absorption spectrum, Fourier infrared spectroscopy, and Raman spectrum measurements. The KAlF4 and Na5Al3F14 phases of the obtained single crystals are determined from the results of XRD. The melting points of KAlF4 and Na5Al3F14 are measured to be ≈549 and ≈705 ℃ from their DTA curves. The maximum matrix phonon energies of KAlF4 and Na5Al3F14 single crystals are 544 and 530 cm–1 from their Raman spectra. The KAlF4 single crystal shows high transmittance from 2000 to 5500 nm, while Na5Al3F14 from 950 to 6000 nm. The energy gaps of KAlF4 and Na5Al3F14 are calculated to be 5.34 and 5.94 eV based on transmission spectra, respectively.