Transparent Glasses and Glass-Ceramics in the Ternary System TeO2-Nb2O5-PbF2.

Juliana Santos Barbosa,Gislene Batista,Gael Poirier,Evelyne Fargin,Thierry Cardinal,Fabia Castro Cassanjes,Sylvain Danto

doi:10.3390/ma14020317

Abstract

Transparent fluorotellurite glasses were prepared by melt-quenching in the ternary system TeO2-Nb2O5-PbF2. The synthesis conditions were adjusted to minimize fluorine loss monitored as HF release. It was found that 10 mol% of Nb2O5 is the optimum content for PbF2 incorporation up to 35 mol% in the tellurite matrix without loss of glass forming ability. Such glass compositions exhibit a wide optical window from 380 nm to about 6 μm. Crystallization properties were carefully investigated by thermal analysis and compositions with higher PbF2 contents exhibit preferential precipitation of lead oxyfluoride Pb2OF2 at lower temperatures. The lead oxyfluoride crystallization mechanism is also governed by a volume nucleation, barely reported in tellurite glasses. Eu3+ doping of these glass compositions also promotes a more efficient nucleation step under suitable heat-treatments, resulting in transparent Eu3+-doped glass-ceramics whereas undoped glass-ceramics are translucent. Finally, Eu3+ spectroscopy pointed out a progressive, more symmetric surrounding around the rare earth ions with increasing PbF2 contents as well as higher quantum efficiencies. These new fluorotellurite glass compositions are promising as luminescent hosts working in the middle infrared.

Highlights

Glass formation was investigated in the ternary system TeO2 -Nb2 O5 -PbF2
Glass formation was investigated in the ternary system TeO2 -Nb2 O5 -PbF2 by meltquenching and it was found that an optimum niobium oxide content of 10 mol% allowed lead fluoride incorporation up to 35 mol%
Synthesis conditions were investigated and optimized to minimize fluorine loss released as HF(g)

Summary

Introduction

The final goal of oxyfluoride glasses is usually related to optical applications since fluoride compounds bring higher optical performances in key areas such as luminescence quantum efficiencies or very low optical attenuations [6], whereas oxide glassy materials are cheaper, easier to prepare, and more thermally and chemically stable for large pieces production or fiber drawing design [7,8,9,10,11,12,13]. Such optical properties can be further improved when heavy metal fluoride nanocrystals are grown in the oxyfluoride glass by suitable heat-treatments. Spatially-controlled precipitation of crystalline fluorides can induce a local refractive index variation in the so-called photothermorefractive glasses with important associated applications such as diffraction gratings or holographic recording [20,21,22,23,24]

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