Authors: Cabral, AA; Balda, R; Fernandez, J; Gorni, G; Velazquez, JJ; Pascual, L; Duran, A; Pascual, MJ

Article.
Crystengcomm. vol: 20. page: 1466-8033.
Date: oct-14. 2018.
Doi: 10.1039/c8ce00897c.

Abstract:
Transparent oxyfluoride glass-ceramics (GCs) were prepared starting from the glass composition 70SiO(2)-7Al(2)O(3)-16K(2)O-7LaF(3) (mol%) doped with four different Nd3+ concentrations (0.1-2 mol%). The glass-ceramics were prepared by heat treatment above the corresponding glass transition temperatures (T-g+ 10-100 degrees C). Depending on the Nd3+ concentration, cubic (alpha-phase) and hexagonal (beta-phase) KLaF4 nanocrystals (NCs) precipitated from the starting glass. By X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM), the crystallization of the cubic structure was observed for all compositions, while beta-KLaF4 nanocrystals were mostly detected for the glass-ceramic samples doped with 0.5 mol% NdF3. This noteworthy result is confirmed by site-selective laser spectroscopy. The presence of alpha-KLaF4 and beta-KLaF4 crystalline phases is unambiguously identified from the emission and excitation spectra and lifetime measurements of the F-4(3/2) state of Nd3+ ions. The spectroscopic results confirm those obtained with XRD and HR-TEM techniques: alpha-KLaF4 NCs are found to be present for all NdF3 concentrations whereas beta-KLaF4 NCs are predominant in the glass-ceramic samples doped with 0.5 mol%..