Spectroscopic probe of rare-earth distribution in transparent oxyfluoride glass-ceramics

Abstract

The growing field of photonics demands the design of new rare-earth (RE)-based optical materials for their use in optical telecommunications, solid state lasers, three-dimensional full-color displays, solar cells, and others. Oxyfluoride glass-ceramics are promising RE hosting candidates since they combine the good chemical and mechanical stability of oxide glass matrixes with the good optical properties of low phonon energy fluoride nano-crystals. In this work, transparent oxyfluoride glass-ceramics obtained by the adequate heat treatment of Nd3+-doped glass with composition SiO2-Al2O3-Na2O-LaF3 are investigated. This glass-ceramic contains very small LaF3 crystals (a10 nm), being LaF3 among the best fluoride hosts for RE ions. Site-selective and time-resolved emissions and excitation spectra of the 4F3/2 and 4F5/2 states, allows to unambiguously isolate the emission of Nd3+ ions in LaF3 nanocrystals which shows extremely well defined spectra, similar to those obtained for pure LaF3 crysta. As an example Fig.1(a) shows the low temperature emission spectra obtained by exciting at 786 and 802 nm for the glass-ceramic sample doped with 0.1 mol% of Nd3+ treated at 620 oC-40h. The spectrum obtained under excitation at 786.5 nm shows sharp peaks. The one at 1039 nm does not overlap with the emission spectrum obtained by exciting at 802 nm. The sharp peaks disappear and the spectrum becomes broader and similar to that found in the glass sample for 802 nm excitation. These results indicate that in the glassceramic samples excited at 786.5, Nd3+ ions are mainly in the crystalline phase. As concentration increases, the emission from Nd3+ ions in the NCs decreases, and the spectra become broader and with less resolved peaks. The excitation spectra also confirm the presence of Nd3+ in the NCs. The low temperature excitation spectra are presented in Fig.1(b) for the GC sample doped with 0.1 mol%. As observed in the spectra obtained at 1039 nm, the low energy band corresponding to the 4I9/2o4F3/2 doublet narrows and defines into two single components as expected for a well defined crystal field site. Moreover, the 4I9/2o4F5/2 band is composed of narrow and well resolved peaks which indicates that the spectra obtained at 1039 nm correspond to Nd3+ ions in the LaF3 nanocrystals. On the other side, the spectra obtained at 1055 nm shows broad bands similar to those found in the glass samples. As concentration increases, the emission from Nd3+ ions in the NCs decreases, and the spectra become broader and with less resolved peaks.