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Volume Bragg gratings (VBGs) recored on photo-thermo-refractive (PTR) glass are extensively utilized in high power lasers, optical communication, holographic display fields, etc. In the majority of application fields, high refractive index modulation (RIM) value and high transmittance are the required parameters for transmission Volume Bragg gratings (TVBGs) devices. This study indicates that the RIM values and transmittance of TVBGs strongly depend on the size and concentration of sodium fluoride (NaF) crystals within the grating periodic structure. Increasing the UV exposure dose causes a reduction in the size of NaF crystals, leading to a finitely rise in the RIM value of TVBGs. Prolonging the crystallization heat treatment time and elevating the temperature effectively enhance the RIM value of TVBGs, which also significantly enlarge the size of NaF crystals in the grating periodic structure. By fine-tuning the process parameters of photothermal induced crystallization, a RIM value of 20–320 ppm is freely controlled. For 1.5 mm thick TVBGs, the above RIM value range can meet the application requirements of achieving high diffraction efficiency in the visible to near-infrared range. Following UV exposure at a dose of 5 J/cm2 and nucleation at 480 °C for 120 min, crystallization treatments at 550 °C for 30–60 min and at 570 °C for 60–120 min are determined as optimal for fabricating TVBGs with high diffraction efficiency and transmittance in the visible (532 nm) and near-infrared (1053 nm) bands, respectively. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glass is a type of functional optical glass material with multi-component and multivalent particles, which is a substrate material for volume Bragg gratings (VBGs) and widely used in high power laser, holography and other applications. Recording VBGs in PTR glass involves photo-thermo-induced crystallization (UV exposure and subsequent heat treatment), while spontaneous crystallization in the unexposed area is one of the important reasons for the light scattering loss of PTR glass, which can also lead to a decrease in the refractive index modulation and absolute diffraction efficiency of the prepared VBGs. In order to optimize spontaneous crystallization of PTR glass, we analyzed the effects of variations in the SiO 2 /Na 2 O ratio on the structure and crystallization behaviors of SiO 2 –Na 2 O–Al 2 O 3 –ZnO–NaF PTR glass using Raman spectroscopy, FTIR spectroscopy, DSC, XRD, and SEM. As the molar ratio (R m) of SiO 2 /Na 2 O increases from 3.37 to 5.38, the polymerization of the silica network structure is significantly enhanced, the crystallization activation energy of original PTR glass increases from 93.52 kJ/mol to 285.23 kJ/mol, and the crystal growth index decreases from 3.57 to 1.49. In the isothermal crystallization process, we observed that increasing the SiO 2 /Na 2 O ratio significantly decreases the grain density and homogenizes the grain distribution of sodium fluoride (NaF) crystals under long-time crystallization conditions, which contributes to maintaining the high transmittance of the crystallized PTR glass in both visible and near-infrared regions. [ABSTRACT FROM AUTHOR]

The oxyhalide photo-thermo-refractive (PTR) glass has found various applications in optical devices. However, due to its complex compositions, researches on the structures and structure-property relationship of this kind of materials is still limited. In this work, we applied molecular dynamics (MD) simulations to investigate the structure of the classic PTR glass (excluding Ce, Ag, Sb, and Sn). A set of bromine-related potential parameters has been developed and tested by comparing the simulated crystal structures with those from experiments or ab initio calculations. The PTR glass has then been simulated by using MD simulations with the newly developed potentials. The structure information of the PTR glass, such as the pair distribution function, bond angle distribution, coordination number, and two-dimensional distributions of elements, have been calculated and compared with available experimental data from literature. In addition, the growth of the fluorine/bromine-rich regions in the PTR glass after heat treatment has also been investigated. It is found that the bromine prefers to stay around the fluorine-rich regions and form the phase boundary between the fluorine-rich phase and the oxygen-rich glass matrix. And the presence of sodium ions in the fluorine/bromine-rich regions increase the aggregation tendency of these regions thus lead to the growth of the region size. The results show that the newly developed bromine/fluorine-related potential parameters can describe the PTR glass structures thus provide a new method to help design and improve new applications. [ABSTRACT FROM AUTHOR]

The well-known standard photo-thermo-refractive (PTR) glass has some limitations in holographic applications in the visible region due to light scattering on the large NaF nanocrystals formed during the photo-thermo-induced (PTI) crystallization process. The large size of the NaF nanocrystals can be reduced by forming more nucleation centers (silver nanoparticles). We suppose this can be achieved by introducing more silver into the batch composition of the glass. However, bromine does not permit high silver concentrations due to the spontaneous crystallization and high Mie-scattering. Therefore, we introduce a novel PTR glass by replacing bromine with chlorine. The novel glass enables us to increase the silver concentration and consequently increase the concentration of the formed nanoparticles. The optical properties, differential scanning calorimetry, and X-ray diffraction analyses were performed on the novel glasses. An experimental and theoretical investigation of the PTI crystallization process was carried out by monitoring the evolution of the surface plasmon resonance (SPR) absorption band. It was found that the UV exposure and heat treatment lead to precipitation of the NaF crystalline phase on a chlorine-containing dielectric shell that surrounds the silver nanoparticle. It was also found that using chlorine instead of bromine leads to a blue shift in the SPR absorption peak location. Volume Bragg gratings were successfully recorded in the novel PTR glasses. The maximum value of the refractive index modulation amplitude obtained for the novel glass is comparable with that for the standard PTR glass. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glass is widely used in volume holographic devices. After photo-thermo treatment, silver nanoparticles (Ag-NPs) and sodium fluoride (NaF) crystals can precipitate in the glass matrix to realize refractive index modulation (RIM). The Ag-NPs are the foundation for subsequent precipitation of NaF crystals and significantly affect the absorption and luminescence characteristics of PTR glass. Within the nucleation temperature range of 440 °C-480 °C, the Ag-NPs formed by photo-thermo-induced nucleation are within 5 nm. Increasing nucleation heat treatment time causes an increase in the average size of Ag-NPs and the thickness of AgBr shell. Increasing the UV exposure dose significantly increases the concentration of Ag-NPs. The long nucleation time and high UV exposure doses can both increase the content of luminescent silver molecular cluster [Ag m ] n+, while high nucleation temperatures over 500 °C cause fluorescence quenching of PTR glass due to the formation of large Ag-NPs over 10 nm and NaF crystals. The formation of Ag-NPs effectively reduces the crystallization temperature of PTR glass. The refractive index of PTR glass can be effectively controlled by adjusting the parameters of photo-thermo-induced nucleation. Under the condition of crystallization at 550 °C for 30 min, a maximum RIM value of 1500 ppm can be achieved. Evolution of silver nanoparticles in PTR glass [Display omitted] [ABSTRACT FROM AUTHOR]

Subject of Research. The paper considers effect of chloride in composition of photo-thermo-refractive glass on the spectral properties of silver nanoparticles formed in ion-exchanged layers after heat treatment. Method. Glasses based on Na2O–ZnO–Al2O3–SiO2–F doped with antimony oxide Sb2O3, cerium oxide CeО2 and a variable chloride content (0–1 mol%) were synthesized for the study. Silver ions were introduced by the low-temperature Na+–Ag+ ion exchange method into the synthesized glasses. For this purpose, glass samples were immersed in a mixture of 0.1AgNO3/99.9NaNO3 (mol%) nitrates at the temperature of 320 °С for 15 minutes. After the ion exchange glasses were irradiated with ultraviolet radiation and heat-treated at the temperature of 500 °C for 3 hours to achieve the growth of silver nanoparticles. Main Results. Spectrum properties of chloride photo-thermo-refractive glasses with silver nanoparticles in ion-exchanged layers are studied. It is found that the presence of chloride in the photo-thermo-refractive glass matrix results in a long-wavelength shift of the absorption band of silver nanoparticles. That may be attributed to the growth of the mixed AgCl/NaCl shell on silver nanoparticles. The formation of silver nanoparticles in ion-exchanged layers occurs both in the irradiated and unirradiated regions of the glass. Practical Relevance. The results can be used to create Bragg gratings inside photo-thermo-refractive glass for input and output radiation (pump and signal) into the waveguide structures formed by the ion exchange method, and to create monolithic integrated optical elements on a single substrate, that is very essential for integrated optics.

In this study, the influence of small additives on the spectral and optical properties of Na+–Ag+ ion-exchanged silicate glass is presented. Polyvalent ions, for example, cerium and antimony, are shown to reduce silver ions to atomic state and promote the growth of photoluminescent silver molecular clusters and plasmonic silver nanoparticles. Na+–Ag+ ion-exchanged and heat-treated glasses doped with halogen ions, such as chlorine or bromine, exhibit formation of photo- and thermochromic AgCl or AgBr nanocrystals. Growth of a silver nanoisland film on the glass surface was observed in the case of undoped sample. The presented results highlight the vital role of small additives to control properties of the silver nanostructures in Na+–Ag+ ion-exchanged glasses. Possible applications of Na+–Ag+ ion-exchanged glass ceramics include but are not limited to biochemical sensors based on surface-enhanced Raman scattering phenomena, temperature and overheating sensors, white light-emitting diodes, and spectral converters. [ABSTRACT FROM AUTHOR]

Neodymium doping of photo-thermo-refractive (PTR) glass leads to a fast non-radiative depopulation of excited states of cerium ions, which are responsible for the glass photosensitivity. The non-radiative energy transfer from cerium to neodymium ions results in a decrease in the efficiency of photoelectron generation under UV irradiation. Emission spectra and fluorescence decay curves of cerium ions under UV excitation were investigated. Absorption spectra of the glasses were obtained as well to distinguish the reabsorption processes and the non-radiative energy transfer mechanisms. It was found that as Nd 2 O 3 concentration increases from 0 to 2 mol%, cerium ions average lifetime decreases from 44.5 to 28 ns, while the energy transfer efficiency reaches 37 %. It was also found that Förster resonance energy transfer may compete with other relaxation mechanisms and the Förster distance for the Ce3+-Nd3+ pair in PTR glass is ∼0.33 nm. This study has important implications for future research; it informs future studies on optimizing the photosensitivity of the PTR glass and choosing rare-earth activators. • Doping of photo-thermo-refractive glass with Nd3+ ions reduces the glass photosensitivity. • Non-radiative ET from Ce to Nd leads to fast depopulation of Ce and decreases the efficiency of photoelectron generation. • Energy transfer efficiency increases from 5 to 37 % when increasing neodymium concentration from 0.25 to 2 mol%. [ABSTRACT FROM AUTHOR]

Microfluidic chips and optical elements can be fabricated based on the nonlinear photosensitivity in photo–thermo–refractive (PTR) glass by controlling the growth of nanocrystals in the femtosecond (fs) laser–irradiated region. Here, we focus on CeO2 and Sb2O3 that play important roles in UV irradiation, experimentally investigate the effects of the dopants on the nonlinear photochemical process in PTR glass triggered by fs Gaussian–Bessel beams. The results show that the generation of Ag0 atoms and the Ag nanoparticles can be improved by CeO2 and Sb2O3 co–doping. Besides, each multivalent ion in PTR glass possibly participates in the electron transfer processes and contributes to the generation of Ag0 atoms. Finally, X–ray diffraction analysis reveals the precipitation of NaF nanocrystals with an average size of 10 to 12 nm after laser irradiation and thermal treatment, which is unrelated to the dopants.

In this study, the influence of small additives on the spectral and optical properties of Na+–Ag+ ion-exchanged silicate glass is presented. Polyvalent ions, for example, cerium and antimony, are shown to reduce silver ions to atomic state and promote the growth of photoluminescent silver molecular clusters and plasmonic silver nanoparticles. Na+–Ag+ ion-exchanged and heat-treated glasses doped with halogen ions, such as chlorine or bromine, exhibit formation of photo- and thermochromic AgCl or AgBr nanocrystals. Growth of a silver nanoisland film on the glass surface was observed in the case of undoped sample. The presented results highlight the vital role of small additives to control properties of the silver nanostructures in Na+–Ag+ ion-exchanged glasses. Possible applications of Na+–Ag+ ion-exchanged glass ceramics include but are not limited to biochemical sensors based on surface-enhanced Raman scattering phenomena, temperature and overheating sensors, white light-emitting diodes, and spectral converters.

A comparative study of spectral-luminescent and Judd–Ofelt analysis of photo-thermo-refractive (PTR) glasses doped with a variable content of neodymium (0.5–2.11 mol%) has been carried out for the first time. The change of Judd-Ofelt parameters (Ω 2 , Ω 4 , Ω 6), radiation lifetime, experimental lifetime, branching ratio and emission cross sections were demonstrated as a function of Nd 2 O 3 concentration and compared to the equivalent parameters in other works. It was found that the 4 F 3/2 → 4 I 11/2 transition is enhanced in Nd-doped PTR glass. The quantum efficiency of 0.5 mol% Nd-PTR for the same transition is 90.3% and the induced emission cross section is 1.743 × 10−20 cm2. The saturation intensity for 4 F 3/2 → 4 I 11/2 laser transition in the same sample is 20.62 kW/cm2, it is lower than that in some commercially produced glasses of same Nd3+-concentration. Laser action of a 0.5 mol% Nd-PTR was demonstrated, it was found that the round-trip loss of this gain medium is 0.34%, this value is quite low, and it is comparable to that in some commercially fabricated Nd-YAG crystals. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glass is a functional optical material with broad applications in holographic optics. In this work, we examine the effect of crystallization heat treatment on the growth and distribution of sodium fluoride (NaF) nano-crystals in PTR glass using DSC, XRD, SEM, and TEM. The optical properties of the crystallized PTR glass are analyzed using a spectrophotometer. The results indicate that the NaF nano-crystals precipitated in PTR glass matrix are in the form of polycrystalline, and the growth of which is highly dependent on temperature. The growth of NaF nano-crystals saturates during the crystalline phase transition, resulting in decreased distribution uniformity. Higher crystallization temperature and longer crystallization time lead to an increase in absorption and scattering losses in the visible band. However, the crystallized PTR glass exhibits favorable absorption and scattering loss characteristics in the near-infrared band. By adjusting the crystallization treatments within the temperature range of 530 °C–570 °C for 10–120 min, refractive index modulation (RIM) values of the transmitting volume Bragg gratings (TVBG) ranging from 50 to 350 ppm can be achieved, which allows for maximum relative diffraction efficiencies exceeding 90% at 532 nm and 1053 nm using different crystallization processes. This research enhances the understanding of NaF nano-crystal growth mechanisms and provides insights into the application of holographic optical elements based on PTR glass in both the near-infrared and visible bands. • NaF nano-crystals exist in polycrystalline form in PTR glass matrix after photo-thermo-induced crystallization. • Diffusion zones will be formed during the later stage of crystallization process, resulting in a "courtyard" structure. • PTR glass accepted short-time crystallization treatments at a low temperature was appropriate for the visible applications. • The crystallized PTR glass exhibits high transmittance (over 80%) and low noise factor in near-infrared applications. • TVBGs with relative diffraction efficiency of over 90% at 532 nm and 1053 nm can be prepared. [ABSTRACT FROM AUTHOR]

Subject of Study.The paper deals with novel research of ion exchange duration influence on spectral-luminescent properties of silver clusters formed in photo-thermo-refractive glass. Method. Photo-thermo-refractive matrix glass based on Na2O–Al2O3–ZnO–SiO2–F (% mol.) system doped with 0,002% mol. of Sb2O3 was synthesized for further research. Silver ions were introduced with low temperature ion exchange method. The glass samples were immersed in the mixture of sodium and silver nitrates 5AgNO3/95NaNO3 (% mol.) at the temperature of 320 °C. Ion exchange duration varied from 5 minutes to 21 hours. Luminescent silver clusters were formed in surface layers of photo-thermo-refractive glass by subsequent heat treatment at the temperature of 450 °C. Main Results. Embedding of silver ions in photo-thermo-refractive glass with ion exchange method led to long-wavelength shift of the UV edge of strong absorption. Location of the UV edge of strong absorption and emission peak of silver clusters depends on ion exchange duration and shifts to the greater wavelengthswith increasing the ion exchange process time. Quantum yield of luminescence decreases significantly according to Stern-Volmer equation with the rising of ion exchange duration. Practical Relevance. Research results can be used for developing white LEDs and down-convertors of solar radiation.

Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass are extensively used for laser beam control applications. As planar holographic optical elements, VBGs operate in the entire spectral window of PTR glass transparency – from near UV, through visible, and up to IR spectral regions. However, complex holographic elements, e.g. lenses or curved mirrors, cannot be fabricated in conventional Ce 3+ doped PTR glass for applications in the visible spectral region due to its photosensitivity being limited to the UV region. Recently developed PTR glass doped with Tb 3+ ions demonstrated sensitivity to visible light. The photo-ionization involves two-step absorption of UV and visible photons via metastable levels of Tb 3+ . Holograms in this glass were recorded by simultaneous exposure to UV radiation from an LED and visible radiation of the second harmonic from a Nd:YAG laser at 532 nm. For the first time holographic lenses operating at 532 nm were demonstrated in PTR glass. This result paves the way for complex holographic optical elements for operation with high power visible lasers. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive multicomponent silicate glass. UV-exposure produces silver nanoclusters, and NaF nanocrystals upon heating, giving rise to permanent refractive index changes. This is the basis for the production of Bragg gratings. In this article, we present a comprehensive overview of the photo-thermo-induced effects in PTR glass. We first give a general introduction of PTR glasses and their applications. Then, we perform a thorough analysis of the mechanisms of refractive index changes starting with the photo-induced process followed by the crystal nucleation mechanism and NaF crystallisation kinetics. Finally, we concentrate on the PTR glass nanostructure and its effect on the crystallisation mechanisms and properties, finishing with the kinetics and origin of the refractive index change. Despite the fact that much is known about this septuagenarian glass and that it is already being commercially produced, a number of open problems still exist that warrant further investigation. [ABSTRACT FROM PUBLISHER]

Dielectric constant spectra of photo-thermo-refractive (PTR) glasses with silver in temperature range of − 50 to + 250 °C and frequency range from 0.1 Hz up to 1 MHz are presented. Glasses without and with silver, after UV irradiation and heat treatments were under study. It is shown that doping of the glasses by a small amount of silver (0.124 mol%) dramatically changes their dielectric characteristics. The influence of halides (Cl, Br) on dielectric characteristics of glasses was investigated. Computer simulations employing the Density Functional Theory (DFT) showed that new relaxation centers, such as subnanosized hybrid molecular clusters like Ag x Na y , charged or neutral, can be formed in the glass. The more complicated complexes like Ag x Na y -Hal (Hal = Cl or Br) can be also formed. [ABSTRACT FROM AUTHOR]

A photo-thermo-refractive glass based on the system Na 2 O/K 2 O/CaO/CaF 2 /Al 2 O 3 /ZnO/SiO 2 doped with Ag 2 O, CeO 2 , SnO 2 , Sb 2 O 3 and KBr was investigated. This glass undergoes a permanent refractive index change after UV irradiation and subsequent two step heat treatment at temperatures above Tg. This is due to the formation of Ag metal clusters which act as nucleation centers for CaF 2 crystallization. Oxidation of Ce 3+ by UV light is the initial reaction and acts as photosensitizer in the glass. The UV–vis absorption spectra during this photo-induced crystallization process were measured. The spectral components that form the absorption spectra of cerium were studied in detail by a band separation with Gaussian functions. Deconvolution of the cerium absorption bands shows an envelope of five spectral components for the trivalent cerium due to the 4f-5d transitions and two spectral components for the tetravalent cerium caused by charge transfer transitions. The effect of different dopants and melting conditions on the photo-thermal process were studied to investigate the influence of glass technology on the photoprocess. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive glasses with cerium oxide as one of dopants inherent in their compositions are now attractive materials for developing various elements and devices of photonics. The effect of variations in the CeO 2 content of the photo-thermo-refractive matrix-based glasses on the spectral and luminescent properties of silver clusters formed in the glasses with the low-temperature ion exchange method is investigated for the first time. Silver clusters in the glasses are shown to manifest themselves in the broadband luminescence in the visible and NIR. The absolute quantum yield of silver cluster luminescence in cerium-doped photo-thermo-refractive matrix-based glasses reaches 32% ( λ ex =360 nm), which can be used effectively for various applications. [ABSTRACT FROM AUTHOR]

A study of the optical, spectral-luminescent and holographic properties of the chlorine-containing photo-thermo-refractive (PTR) glass doped with neodymium ions was carried out. The chlorine-containing PTR glass has been recently produced by replacing the bromine in the standard PTR glass with chlorine. The glass was doped with different concentrations of neodymium ions. The spectroscopic analysis of neodymium in the glass has been performed using the Judd-Ofelt theory based on experimental absorption and emission measurements. Spectroscopic parameters, such as the Judd-Ofelt intensity parameters, radiative and non-radiative transition probabilities, fluorescence lifetimes, stimulated emission cross-sections, and branching ratios, were obtained and found to be comparable with the parameters of the standard PTR glass doped with neodymium. The mechanism of non-radiative energy transfer was analyzed based on the lifetime kinetics measurements. It was found that cross-relaxation among neodymium ions is the dominant non-radiative energy transfer mechanism. Holographic characteristics of the chlorine-containing PTR glasses doped with neodymium have been also studied. The volume Bragg grating was recorded in the doped and undoped glasses. It was found that the UV exposure and heat treatment do not change the spectroscopic characteristics of neodymium ions in the glasses, while the neodymium ions reduce the sensitivity of the glass. The energy transfer from cerium to neodymium when irradiating using the 325-nm laser makes the hologram recording possible on the samples of low neodymium concentrations only. Studying the spectroscopic and holographic properties of the chlorine-containing PTR glass doped with neodymium ions demonstrates the potential of using such a material in the applications of photonics integration and monolithic optical devices like distributed-feedback lasers. • Spectroscopic properties of Nd ions in Cl-PTR glass are comparable to those of Nd in the standard (Br-PTR) glass. • VBG was recorded in the undoped Cl-PTR glass, as well as in the glass doped with Nd. • UV exposure and heat treatment do not affect the spectral-luminescent properties of Nd in the Cl-PTR glass. • Nd reduces the photosensitivity of Cl-PTR due to energy transfer from Ce to Nd during the hologram recording at 325 nm. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glass is a kind of photo-thermo-sensitive silicate glass. After photo-thermo treatment, it can precipitate sodium fluoride (NaF) crystals in the glass matrix to change the refractive index, which is widely used in volume holographic devices. The purpose of this paper is to study the effect of photo-thermo-induced nucleation on the crystallization kinetics of PTR glass, and several techniques, such as SEM, DSC, absorption spectrum, and XRD, are used to analyze the properties of the induced nucleation process. The results show that photo-thermo-induced nucleation can significantly change the crystallization ability of PTR glass and affect the size, morphology, and volume fraction of precipitated NaF crystals. The reason lies in the change in the composition and number of silver nuclei under different photo-thermo-nucleation treatment systems. According to the obtained results, the photo-thermo-induced nucleation processes of PTR glass will be helpful for improving the properties of volume Bragg gratings (VBGs) and other optical elements based on PTR glass. • The isothermal and non-isothermal crystallization experiment were carried out. • The crystallization activation energy of PTR glass was calculated by Kissinger formula. • The composition of silver nucleus was analyzed by absorption spectrum. • The volume fraction of NaF crystals was quantitatively analyzed by XRD. • The nano NaF crystals embedded in PTR glass matrix was clearly photographed. [ABSTRACT FROM AUTHOR]

Photo-thermo-refractive (PTR) glasses are the class of polyfunctional materials that combine the properties of several monofunctional materials such as photo-refractive, laser, luminescent, and plasmonic ones. Based on PTR glasses, various diffractive holographic elements and photonic devices were developed in both the volume and fiber versions. In this paper, the fabrication of optical planar waveguides on PTR glass by low-temperature ion exchange is reported for the first time. Planar waveguides were fabricated through substituting the sodium ions in glass by silver, potassium, rubidium, and cesium ones from the nitrate melts. The silver waveguides were shown to have the largest depth (27 μm) and reveal no birefringence. For the silver waveguides, an increase in the refractive index is caused by differences in the polarizabilities of cations exchanged. The maximum increment of the refractive index was observed in the cesium waveguides (0.0512). An increase in the refractive index and also appearing the birefringence in potassium, rubidium, and cesium waveguides are found to be due to the compressive mechanical stresses and their relaxation. The potentialities of the ion exchange technology for fabricating, in PTR glasses, planar gradient waveguides with low losses (0.5 dB/cm) are demonstrated, the potentialities extending the application field of PTR glasses in photonics. [ABSTRACT FROM PUBLISHER]

A spectroscopic investigation of luminescent centers transformation in photo-thermo-refractive glass by using ultraviolet (UV) nanosecond laser pulses with radiation wavelength 355 nm was performed. Initially the glass was irradiated by UV lamp and thermal-treated that causes a neutral silver molecular clusters luminescence in a visible spectral region. After the laser irradiation a luminescence quenching was observed in the irradiated region. The thermal treatment below glass transition temperature restores the luminescence of silver molecular clusters with complex spatial distribution of luminescence intensity inside the irradiated region. UV lamp irradiation achieves the same result without any inhomogeneity. The observed effects are caused by photoionization and reduction of subnanosized silver molecular clusters with the participation of cerium and antimony ions. [ABSTRACT FROM AUTHOR]

An innovative type of optical component--a volume Bragg grating--has recently become available commercially and has found wide applications in optics and photonics due to its unusually fine spectral and angular filtering capability. Reflecting volume Bragg gratings, with the grating period gradually changing along the beam propagation direction (chirped Bragg gratings--CBGs) provide stretching and recompression of ultrashort laser pulses. CBGs, being monolithic, are robust devices that have a footprint three orders of magnitude smaller than that of a conventional Treacy compressor. CBGs recorded in photo-thermo-refractive glass can be used in the spectral range from 0.8 to 2.5 µm with the diffraction efficiency exceeding 90%, and provide stretching up to 1 ns and compression down to 200 fs for pulses with energies and average powers exceeding 1 mJ and 250 W, respectively, while keeping the recompressed beam quality M² < 1.4, and possibly as low as 1.1. This paper discusses fundamentals of stretching and compression by CBGs, the main parameters of the gratings including the CBG effects on the laser beam quality, and currently achievable CBG specifications. [ABSTRACT FROM AUTHOR]

Abstract: The luminescence spectra of silver molecular clusters in photo-thermo-refractive glasses are investigated in detail before and after the UV irradiation and also after the heat treatment of the samples. In the initial photo-thermo-refractive glass sample, silver is shown to occur in the form of Ag+ ions and positively charged molecular clusters. After the UV irradiation with the wavelength corresponding to the Ce3+ ion absorption, these species are assumed to pass partially to the neutral state, thus forming the Ag0 atoms and neutral molecular clusters such as Ag2, Ag3, and Ag4 that exhibit an intense luminescence in the visible. A subsequent heat treatment at temperatures below the glass transition one results in an increase in the intensity of the luminescence due to an increase in the concentration of neutral molecular clusters. Also investigated are the influence of halogens such as Cl and Br in glass matrix composition on the luminescence of silver molecular clusters in photo-thermorefractive glasses and the effect of temperature on the luminescence spectra of photo-thermorefractive glasses. [Copyright &y& Elsevier]

Abstract: The effects of the silver ion exchange and of subsequent UV irradiation and/or heat treatment on the optical density spectra of photo-thermo-refractive matrix glass samples both virgin and doped with cerium and/or antimony oxides were investigated. The incorporation of silver by ion exchange for ~15min at 310°C was found to cause, for all glasses except those with CeO2 content around 0.1mol% or more, a shift of the UV limit of strong absorption to the greater wavelengths by ~70–100nm due to the occurrence of Ag+-related absorption. Complicated changes caused by the UV irradiation and/or heat treatment of ion-exchanged samples in the location of their UV limit of strong absorption and in the absorption throughout the 330–550nm region were analyzed and shown to be greatly influenced by (i) the kind of dopant(s), (ii) chances for shifting the redox and other equilibria involving the dopants at temperatures of particular treatment processes, and (iii) NaBr presence in the glass batch composition. The effect of NaBr addition was explained tentatively in terms of formation, after the heat treatment, of AgBr clusters or nanocrystals. [Copyright &y& Elsevier]

Abstract: The UV absorption spectra of cerium-doped photo-thermo-refractive matrix glasses were recorded and processed with the dispersion analysis based on Convolution model for the complex dielectric function. It was confirmed that the absorption maxima in the UV spectra of PTR matrix glasses related to the Ce3+ and Ce(IV) valence states are the envelopes of at least three spectral components each. The inherent frequencies of three Ce3+- and three Ce(IV)-related oscillators are shown to be located in the 31,200–34,900 and 38,400–49,800cm−1 wavenumber regions, respectively. The occurrence of three Ce3+-related spectral components was interpreted, based on an analogy with the spectra of cerium-doped crystals, in terms of splitting the excited 2 D state by the non-central Coulomb and spin–orbit interactions into three levels. Beer Law was shown to be obeyed, for both the Ce3+ and Ce(IV) species, throughout the entire range of CeO2 content of samples studied. The total molar absorptivity of the strongest Ce(IV)-related oscillator was found to exceed that of the strongest Ce3+-related one by approx. 16 times. The trivalent antimony was shown to play the role of a reducer with respect to the Ce(IV) valence state. [Copyright &y& Elsevier]

Silver nanoparticles destruction process in photo-thermo-refractive glass under nanosecond pulsed laser irradiation (532nm) depending on exposure dose is investigated. It is shown that photo fragmentation of silver nanoparticles and formation of silver clusters as well as the photoionization of silver neutral atoms with their transition into ion state takes place under laser radiation.

Abstract: Photo-thermo-refractive (PTR) glass demonstrates refractive index change after exposure to UV radiation followed by a thermal treatment that enables recording of high efficiency holographic optical elements. This work demonstrates feasibility of function of this material as a complex optical medium which posseses both photosensitive and luminescent properties and paves a way for creation of monolythic solid state lasers where resonator components can be holographically recorded inside of a laser medium. It was found, that incorporating of Nd3+ ions in PTR glass does not affect photosensitivity required for hologram recording. It was demonstrated that emission wavelength, spectral width, and cross section of Nd3+ luminescence in PTR glass are typical for silicate laser glasses and Nd-doped PTR glass can be considered as a promising laser medium for monolithic solid state lasers. [Copyright &y& Elsevier]

Abstract: The paper opens up a series of papers on the origin and parameters of spectral features forming the absorption of photo-thermo-refractive (PTR) glasses in the UV. Problems to be cleared for gaining further insight into the spectroscopic manifestations of species responsible for the photo-induced processes in PTR glasses are discussed. The samples of bromine-containing and bromine-free PTR glass matrices are synthesized and their absorption spectra in the 28,500 to 50,000cm–1 region are recorded. The dispersion analysis of the spectra is conducted based on the convolution model for the complex dielectric function of glasses. The matrix electronic transitions that set the real part of the complex dielectric function and form the intrinsic absorption tail of the matrix are simulated with a series of effective oscillators. Spectral features forming the total absorption spectrum of PTR glass matrices in the 28,500 to 50,000cm–1 region are deconvoluted. These features are (i) the intrinsic absorption tail, (ii) for the bromine-containing matrix, the low-wavenumber wing of an envelope around ~51,400cm–1 covering the bromine-related spectral feature(s), (iii) Fe2+- and Fe3+-related impurity bands, and also (iv) a structureless absorption mostly due to the high-wavenumber wings of other impurity bands below 28,500cm–1. [Copyright &y& Elsevier]

Abstract: We present the experimental investigation of formation and growth of Ag nanocrystals in silica photo-thermo-refractive glasses under the electron-beam irradiation and subsequent thermal treatment. The influence of electron irradiation fluence, current density and thermal treatment conditions on nanocrystal growth dynamic has been investigated. Theoretical models and computer simulation of main processes which take place during electron-beam irradiation are presented. [ABSTRACT FROM AUTHOR]

Abstract: Nonlinear properties of a photo-thermo-refractive (PTR) glass are studied and compared with those in fused silica and a conventional optical glass. PTR glass is a new photosensitive medium for high-efficiency phase volume hologram recording which manifests a linear refractive index modulation after exposure to UV radiation followed by thermal treatment. Nonlinear optical properties of PTR glass exposed to femtosecond laser pulses are studied. Diffraction patterns in a propagated laser beam focused in the sample were detected by a CCD, while a nonlinear refractive index was measured by a collinear-orthogonal-polarization-pump-probe (COP3) method. It was found that nonlinear refractive index of PTRG is n 2 =3.3×10−20 m2/W (0.33ppmcm2/GW) which is about the same as for the fused silica. It is important that n 2 in PTR glass does not vary after UV exposure and thermal development. [Copyright &y& Elsevier]

Kinetics of photoinduced process is studied in a new photosensitive material for volume hologram recording which is a photo-thermo-refractive glass (PTRG). A system of balance equations is derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+)+. The main approach for the system solution is a calculation of low quasistationary concentration of free electrons in a conduction band, while concentrations of generated electron and hole centers are expected to be variable. A general solution of a system is found as a combination of exponential and hyperbolic functions. It is shown that an exponential solution is the result of the absence of a re-trapping of electrons, while a pure hyperbolic solution occurs in the case of equal probability of trapping and re-trapping. The approach developed for the first stage of photo-thermo-refractive process which is photoionization and trapping, is applied for the modeling of the final result of the whole process of photo-thermo-induced refractive index transformation in glass. It is found that the refractive index increment in PTRG is better described by hyperbolic function compare to the exponential one. Kinetic parameters of induced refraction in PTRG are determined. [Copyright &y& Elsevier]

• We developed a chloride photo-thermo-refractive glass doped with ytterbium ions. • Spectroscopic and gain properties of ytterbium ions in chloride photo-thermo-refractive glass were carried out. • Ytterbium-doped chloride photo-thermo-refractive glass is a promising candidate material for laser and gain applications. We developed a new chloride photo-thermo-refractive glass doped with ytterbium ions. The dependence of optical and spectral-luminescent characteristics on ytterbium concentration has been studied. Concentration dependence of excited state decay time has been analyzed taking into account the self-trapping and self-quenching mechanisms. The optimum concentration of ytterbium ions in chloride photo-thermo-refractive glass has been determined. Other important spectroscopic parameters such as absorption and emission cross-sections, radiative lifetimes, pump saturation, and minimum pump intensities have been obtained using absorption and emission measurements and theoretical approaches such as Fuchtbauer-Landenburg and McCumber theories. The evolution of the gain cross-section spectrum as a function of a population inversion parameter has been performed. Results of this study show that the ytterbium-doped chloride photo-thermo-refractive glass demonstrates good spectroscopic and luminescent properties for laser and gain application. [ABSTRACT FROM AUTHOR]

Microfluidic chips and optical elements can be fabricated based on the nonlinear photosensitivity in photo–thermo–refractive (PTR) glass by controlling the growth of nanocrystals in the femtosecond (fs) laser–irradiated region. Here, we focus on CeO2 and Sb2O3 that play important roles in UV irradiation, experimentally investigate the effects of the dopants on the nonlinear photochemical process in PTR glass triggered by fs Gaussian–Bessel beams. The results show that the generation of Ag0 atoms and the Ag nanoparticles can be improved by CeO2 and Sb2O3 co–doping. Besides, each multivalent ion in PTR glass possibly participates in the electron transfer processes and contributes to the generation of Ag0 atoms. Finally, X–ray diffraction analysis reveals the precipitation of NaF nanocrystals with an average size of 10 to 12 nm after laser irradiation and thermal treatment, which is unrelated to the dopants. [ABSTRACT FROM AUTHOR]

Structural changes in silver-containing photo-thermo-refractive (PTR) silicate glasses during photo-thermo-crystallization process were studied by methods of Raman spectroscopy. Raman spectra were measured in frequency ranges 300-700 cm−1 and 900-1300 cm−1 after UV irradiation and subsequent thermal treatments at T = 360 OC and 510 OC. Raman spectra of silver-containing PTR glass were compared with Raman spectra of glasses without Ag, and glasses without Ag, Ce and Sb. It was shown that mentioned external treatments result in the sequence of structural changes, which may be interpreted as breaks and restoration of siloxane rings, appearance of new rings, appearance and disappearance of non-bridging oxygen centers. These processes can influence on the features of photo-thermo-crystallization processes in PTR glasses. • Raman spectra of silver-containing photo-thermo-refractive glass. • Effect of UV irradiation on Raman spectra on photo-thermo-refractive glass structure. • Effect of thermal treatments on Raman spectra on photo-thermo-refractive glass structure. • Analysis of structural changes in photo-thermo-refractive glass during external treatments. [ABSTRACT FROM AUTHOR]

Silver nanostructures, including molecular clusters and plasmonic nanoparticles, attract much attention due to their unique optical properties and potential applications in various fields. Glasses doped with silver molecular clusters are known to possess bright luminescence under UV excitation, which opens up prospects of using the glasses as solar spectral converters to overcome poor spectral response for most of photovoltaic cells in the short‐wavelength region. In this study, silver molecular clusters are formed in photo‐thermo‐refractive glass matrix both by UV irradiation and by Na+↔Ag+ ion exchange and optically characterized. Photo‐thermo‐refractive glasses doped with silver molecular clusters, independently on silver introduction method, are shown to demonstrate broad absorption in the UV, intense white emission under excitation at 360 nm, and high photoluminescence quantum yield that meet requirements for luminescence downshifting materials. Despite this, only photo‐thermo‐refractive glass with silver molecular clusters uniformly distributed in the glass volume enhances the output power of a silicon photovoltaic cell, thus showing the potential for future application of photo‐thermo‐refractive glasses in photovoltaics, particularly in case of further experiments. UV‐excited luminescent materials receive special attention in recent years due to the potential application as downconverters for photovoltaic cells. Glass doped with luminescent silver clusters is a promising material to play this role. Silver clusters formed in matrix of photo‐thermo‐refractive glass by two different approaches is studied to verify compliance with requirements for luminescence downshifting materials. [ABSTRACT FROM AUTHOR]