Abstract
Photo-thermo-refractive (PTR) glass is a photosensitive multi-component silicate glass that exhibits refractive index change after successive UV-exposure and thermal treatment. The refractive index change was demonstrated to be associated with the precipitation of NaF nano-crystals in the glass matrix. This paper presents a systematic study of the dependence of the refractive index change on dosage of UV-exposure and thermal treatment duration and temperature in already UV-exposed and nucleated samples. It is shown using Avrami plots that the refractive index change in PTR glass is determined by a diffusion-controlled growth of particles from pre-existing nuclei while all coefficients have exponential dependence on temperature (Boltzmann law). The developed model, which includes both photo-chemistry and crystallization processes, allow describing the refractive index change dependence on dosage for a wide range of thermal treatment duration and temperature and an accuracy better than 10%.
Highlights
The refractive index change was demonstrated to be associated with the precipitation of NaF nanocrystals in the glass matrix
This paper presents a systematic study of the dependence of the refractive index change on dosage of UV-exposure and thermal treatment duration and temperature in already UV-exposed and nucleated samples
It is shown using Avrami plots that the refractive index change in PTR glass is determined by a diffusion-controlled growth of particles from pre-existing nuclei while all coefficients have exponential dependence on temperature (Boltzmann law)
Summary
The evolution of the material’s nanostructure and optical properties after UV-exposure and thermal treatment are reported in several publications e.g [6,10,11,12,13,14]. It was shown in [6] that the photosensitivity of PTR glass results from the precipitation of nano-sized sodium fluoride crystals within the glass matrix in the UV-exposed regions after heat treatment. The second part of the crystallization process consists in the heterogeneous precipitation and growth of sodium fluoride crystals on top of the silver (or silver bromide) clusters.
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