N. V. Nikonorov

Formation of Silver Nanoparticles on the Silicate Glass Surface after Ion Exchange

It has been experimentally shown that water vapor thermal treatment of silicate glasses with silver ions introduced by ion exchange leads to the formation of a silver nanoparticle layer with a high packing density on the glass surface. The results of studying the morphology of samples by atomic force and electron microscopy and X-ray spectral analysis of the composition of nanoparticles, as well as the optical density and luminescence spectra in different stages of the treatment, are presented. Mechanisms explaining the processes responsible for silver nanoparticle formation upon water vapor thermal treatment on the glass surface after ion exchange are proposed.

Influence of Glass Composition on the Refractive Index Change upon Photothermoinduced Crystallization

The influence of the main components (SiO2, Al2O3, ZnO, and Na2O) of a photothermorefractive glass matrix and Br–ions on the change in the refractive index is studied in the course of photothermoinduced crystallization in glasses. The optimum concentrations of these components at which the change in the refractive index is maximum are determined. The regularities revealed are explained within the modern concepts of the structure of polychromatic glasses and the nature of the photothermorefractive effect.

Influence of UV irradiation and heat treatment on the luminescence of molecular silver clusters in photo-thermo-refractive glasses

The luminescence spectra of photo-thermo-refractive (PTR) glasses containing cerium, silver, and antimony ions before and after UV irradiation and after heat treatment have been thoroughly investigated for the first time. It is shown that silver is present in the initial PTR glass in the form of ions and positively charged molecular clusters. After UV irradiation into the absorption band of cerium ions, silver partially passes to the neutral state in the form of atoms and neutral molecular clusters Ag2, Ag3, and Ag4, which exhibit bright luminescence in the visible spectral range. Subsequent heat treatment at a temperature below the glassformation temperature leads to an increase in the luminescence intensity due to the increase in the concentration of neutral molecular clusters. Heat treatment at a temperature above the glass-formation temperature leads to the formation of silver nanocrystals and luminescence quenching. It is proposed to use PTR glasses with molecular silver clusters as phosphors for converting UV radiation into the visible range for solar power engineering and white LEDs.

Characterization of non-linear upconversion quenching in Er-doped glasses: modeling and experiment

Non-linear upconversion quenching in highly Er-doped glasses has been studied with use of Monte-Carlo modeling and a new experimental steady-state technique. The experimental and simulated results exhibit that the upconversion coefficient depends on the following factors: (a) erbium content, (b) migration of excitation, (c) pump power, and (d) duration of pump pulse.

Effect of a dielectric shell of a silver nanoparticle on the spectral position of the plasmon resonance of the nanoparticle in photochromic glass

The behavior of the spectral position of the absorption band of colloidal silver in photochromic glass is analyzed in relation to the variation in the refractive index of a thin layer of the medium (shell) that surrounds silver nanoparticles. It is shown that the appearance of a shell with a high refractive index leads to a long-wavelength shift in the plasmon absorption band of silver nanoparticles. These results make it possible to explain particular features of the absorption spectrum of photothermorefractive glasses.

Holographic characteristics of a modified photothermorefractive glass

The spectral and holographic characteristics of classical and modified photothermorefractive glass are compared. It shows that modified photothermorefractive glass has no additional absorption bands in the blue–green region, as is the case in classical photothermorefractive glass. This makes it possible to record purely phase holograms in modified photothermorefractive glass. The refractive-index increment is a factor of 2 greater in modified photothermorefractive glass than in classical photothermorefractive glass.

Monte-Carlo simulation of upconversion processes in erbium-doped materials

Abstract Nonlinear upconversion quenching in Er-doped materials has been studied with use of Monte-Carlo modeling. Structure models allowed one to consider homogeneous Er3+ ions space distributions as well as clustering. Two variants of the simulation algorithm have been developed which took into account an evolution of one excitation or evolutions of all excitations simultaneously. The obtained results provided quantitative data on the influence of the following factors on the upconversion efficiency: (a) erbium content, (b) migration of excitation, (c) pump power, and (d) duration of pulse pumping.

Luminescence of molecular silver clusters in oxyfluoride glasses

Luminescence spectra of silver-containing oxyfluoride glasses have been investigated in the excitation spectral range of 360–480 nm. Analysis of the luminescence spectra shows that silver in oxyfluoride glasses that contain no strong reducers and were subjected to heat treatment affecting redox processes exists in the form of neutral atoms and neutral molecular Ag2, Ag3, and Ag4 clusters.

Broadband copper luminescence in potassium-aluminum borate glasses

Broadband luminescence in the visible spectral range has been investigated for copper-containing potassium-aluminum borate glasses. It is shown that the luminescence in initial glasses (before their heat treatment) is due to the presence of molecular clusters Cun (n < 10) in them. Chemical reactions during heat treatment lead to the formation of CunClx and CunOx clusters with luminescence bands lying in the spectral range of 450–600 nm.

Spectral components that form UV absorption spectrum of Ce3+ and Ce(IV) valence states in matrix of photothermorefractive glasses

We have measured the UV absorption spectra of photothermorefractive glasses of the system Na2O-ZnO-Al2O3-NaF-SiO2 doped by cerium oxide in the range of (2.8–5.0) × 104 cm−1 (360–200 nm). The spectra have been processed by the method of dispersion analysis based on the analytical convolution model for the complex dielectric function of glasses. We show that the absorption band centered at 3.3 × 104 cm−1 (∼303 nm) that is attributed to the transition 2F5/2 → 5d in the Ce3+ ion, is an envelope of three spectral components. The broad absorption range (3.5–4.7) × 104 cm−1 (200–270 nm) that is commonly interpreted as a charge transfer band of the Ce(IV) valence state, is an envelope of at least three spectral components.