Rare-Earth-Activated Fluorophosphate Glasses: Local Environment of the Activator and Capture Volume Model

Abstract

Data are presented on the induced optical absorption and EPR in Ba(PO 3 ) 2 -MgF 2 glasses activated with Tb 2 O 3 and Eu 2 O 3 . The effect of activator concentration on the EPR spectra of the ê and ê centers in glasses differing in fluoride content is analyzed. The results indicate that fluorophosphate glasses can be characterized by two capture volumes which may differ several times, depending on the activator concentration. At low activator concentrations, corresponding to the largest capture volume, the activator ions seem to be in a phosphate environment. The maximum Tb 3+ concentration is comparable to the Eu 3+ concentration at which the luminescence spectrum points to a phosphate environment of the rare-earth ion. O 4 2-O 3 2-

Network Structure and Rare-Earth Ion Local Environments in Fluoride Phosphate Photonic Glasses Studied by Solid-State NMR and Electron Paramagnetic Resonance Spectroscopies

“…53 No clear evidence is observed for P-bonded fluorine atoms, whose resonance signal would be expected near -75 ppm. 54,55 As documented by previously published 19 F{ 31 P} REDOR experiments on the x = 20 sample, 34 no rapidly decaying signal owing to P-bonded F-atoms could be observed. Based on this result, we conclude that these species do not make a significant contribution to the glass structure.…”

“…The components SrF 2 , BaF 2 and YF 3 may be considered as network modifiers, which might act to depolymerize the glass structure by breaking either P-O-P or P-O-Al linkages. As neither the 19 F MAS NMR, the Raman spectra nor the (previously reported) 19 F{ 31 P} REDOR data show any evidence of P-F bonding, 34 Yb 3+ is an S = ½ ion. The 4f configuration gives rise to a 2 F 7/2 term in the ground state and a 2 F 5/2 term in the first excited state.…”

“…For increasing x the 27 Al isotropic chemical shift values tend to increase, indicating an increasingly strong interaction with 19 F nuclei (see figure 4b). This behavior is consistent with our 27 Al-31 P double NMR results discussed in the following section.…”

“…Such resonances in the diagonal region of the spectra indicate that the electron-nucleus interaction for these species fulfill the conditions of the weak coupling-limit, in agreement with the ESEEM data discussed above. In addition, the 19 the simulations in Figure 12 can be compared to the experimental data of the whole set of samples. In order to reproduce the experimental data in both ESEEM and HYSCORE experiments, the simulations should consider that each Yb 3+ ion is interacting with two distinct types of 19 F nuclei: a strongly coupled one, giving rise to the split signal and a weakly coupled one, with its resonance at the 19 F nuclear Zeeman frequency.…”

“…Solid state 31 P and 27 Al NMR studies were carried out on a Bruker Avance III spectrometer operating at 400 MHz, equipped with a 4 mm probe which was operated at spinning speeds up to 14.0 kHz. 19 Chemical shifts are reported relative to CFCl 3 using solid AlF 3 as a secondary reference (-172 ppm). 27 Al MAS-NMR spectra were recorded using short pulses of 1 µs length and a relaxation delay of 10 s. 27 Al triple-quantum (TQMAS) NMR data were obtained using the three-pulse z-filtering sequence, 35 using hard excitation and reconversion pulses of 5 µs and 2 µs length and soft detection pulses of 10 µs length.…”