Effects of Tm 3+ Additions on the Crystallization of LaF 3 Nanocrystals in Oxyfluoride Glasses: Optical Characterization and Up‐Conversion

The influence of the addition of 1 mol% Tm 2 O 3 on the nanocrystallization of LaF 3 in a glass of composition 55 SiO 2 –20 Al 2 O 3 –15 Na 2 O –10 LaF 3 (mol%) has been studied. Tm 2 O 3 affects the phase separation in the glass and delays the onset of crystallization with respect to the undoped glass. Additionally, the maximum LaF 3 crystal size is slightly greater than that in the undoped glass–ceramics. The microstructural and compositional changes in the glass matrix have been studied using several techniques, including viscosity, dilatometry, X‐ray and neutron diffraction ( XRD , ND ), quantitative Rietveld refinement, transmission electron microscopy ( TEM ), differential scanning calorimetry ( DSC ), and Raman spectroscopy. Photoluminescence measurements indicate that the Tm 3+ ions are distributed between the glassy matrix and LaF 3 crystals. Eu 2 O 3 has been used as structure probe and part of the Eu 3+ ions are reduced to Eu 2+ when incorporated in the LaF 3 nano‐crystals. Up‐conversion spectra under IR ‐excitation show a higher intensity of the blue emission in the Tm ‐doped glass–ceramic compared with that in the glass.