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

Abstract Highly transparent KAlF 4 and Na 5 Al 3 F 14 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 KAlF 4 and Na 5 Al 3 F 14 phases of the obtained single crystals are determined from the results of XRD. The melting points of KAlF 4 and Na 5 Al 3 F 14 are measured to be ≈549 and ≈705 ℃ from their DTA curves. The maximum matrix phonon energies of KAlF 4 and Na 5 Al 3 F 14 single crystals are 544 and 530 cm –1 from their Raman spectra. The KAlF 4 single crystal shows high transmittance from 2000 to 5500 nm, while Na 5 Al 3 F 14 from 950 to 6000 nm. The energy gaps of KAlF 4 and Na 5 Al 3 F 14 are calculated to be 5.34 and 5.94 eV based on transmission spectra, respectively.