Gd-based oxyfluoride glass ceramics: Phase transformation, optical spectroscopy and upconverting temperature sensing

摘要

A series of precursor glasses with compositions of SiO2-Al2O3-AlF3-Na2O-NaF-Gd2O3/GdF3-YbF3-ErF3 were prepared and their crystallization behaviors were investigated. For the samples with high F content, meta-stable hexagonal GdF3 nanocrystals were preferentially precipitated from glass matrix and decreasing F/O ratio induced phase transformation to cubic NaGdF4 and finally to hexagonal NaGdF4. Benefited from its multiple active sites, significant enhanced upconversion luminescence was achieved for Yb/Er co-doped glass ceramic containing hexagonal NaGdF4 nanocrystals. Importantly, significant temperature-sensitive upconversion fluorescence intensity ratio between Er3+: H-2(11/2) -> I-4(15/2) transition (520 nm) and S-4(3/2) -> I-4(15/2) one (540 nm) was detected owing to the competitive radiation transitions from these two thermally coupled emitting-states. Furthermore, linear temperature-dependent fluorescence intensity ratio between Er3+: F-4(9/2) -> I-4(15/2) transition (650 nm) to S-4(3/2) -> I-4(13/2) one (540 nm) was achieved, showing the advantages of high sensitivity, superior signal discriminability as well as excellent thermal stability for temperature determination. (C) 2017 Elsevier Ltd. All rights reserved.