Nanocrystals In Glass Matrix Research Articles

EPR, NMR, DFT and XPS study on LaAlO3 phase transition in glass and influence on glass structure and properties

Thermal treatment induced phase transition of LaAlO3 in glass and its influence on glass structure and dielectric, magnetic, and Faraday rotation properties were characterized through various techniques such as nuclear magnetic resonance, X-ray neutron diffraction, transmission electron microscopy, X-ray photoelectron microscopy, vibrating-sample magnetometer, and electron paramagnetic resonance. Cubic LaAlO3 nanocrystals were synthesized and incorporated into lead-tellurite glasses, after crystallization treatment at 380 °C for 2 h, 14-17 nm-cubic LaAlO3 nanocrystals were changed to 14-27 nm-rhombohedral LaAlO3 perovskite due to the temperature-induced viscosity and strain in the melt. The phase transition of LaAlO3 nanocrystals in glass matrix was verified through versatile techniques in terms of the octahedral AlO6 distortion, SAED patterns, changes of lattice parameters calculated by Rietveld refinement, and coordination number changes of AlO6 by NMR and XPS techniques. The modification to the glass structure was yielded by phase transition through converting TeO4→TeO3, AlO6→AlO4, BO4→BO3, and producing non-bridging oxygen. In addition, the energy band gap and density of states of glass after phase transition was calculated through Density functional theory (DFT) simulation. Glass doped with 10% LaAlO3 exhibited a promising dielectric constant and good thermal stability due to the phase transition induced polarizability, and improved optical and magnetic performance which is promising for photonics device applications.

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

AbstractLi2O–Al2O3–SiO2‐based glass–ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire‐safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics were prepared by conventional melt‐quenching and subsequent heat‐treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass–ceramics was highly dependent on MgO/Li2O ratios in glass components and heat‐treatment temperatures, corresponding with the crystal phases in glass–ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass–ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy‐dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass–ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.

Submillisecond Spin Relaxation in CsPb(Cl,Br)3 Perovskite Nanocrystals in a Glass Matrix.

Lead halide perovskite nanocrystals in a glass matrix are a promising platform for optoelectronic applications due to their excellent optical properties combined with outstanding stability against the environment. We reveal the potential of this system for spintronics by studying the electron spin properties of CsPb(Cl,Br)3 nanocrystals in a fluorophosphate glass matrix. Using optical spin orientation and spin depolarization with a radio frequency field, we measure longitudinal spin relaxation time, T1, reaching several hundreds of microseconds at low temperatures. This time T1 corresponds to a spin state with a small g factor, which we attribute to a weakly exchange-coupled electron-hole pair with antiparallel spins.

Structure of glasses and composites in As<sub>2</sub>S<sub>3</sub>–Sb<sub>2</sub>S<sub>3</sub>–SbI<sub>3</sub> system

Purpose. Composites on the basis x (As 2 S 3 ) y (Sb 2 S 3 ) z (SbI 3 ) glasses are suitable for creation of ferroelectric glassceramics, nonlinear dielectrics, memory media, elements for infrared and nonlinear optics, various sensors. This paper presents the results of thermal, X-ray diffraction and Raman studies of the conditions of formation and nature of crystalline inclusions in the glass matrix of the As 2 S 3 -Sb 2 S 3 -SbI 3 system during their thermal treatment. Methods. Differential thermal analysis (DTA), Raman and X-Ray diffraction spectroscopy. DTA curves were carried out in the temperature interval of 293–700 K. Heating rate was equal 3 K/min. Results. Danoheterogenous structure of glasses in As 2 S 3 -Sb 2 S 3 -SbI 3 system established on the basis of Raman spectra investigations. Their structural network is formed by only binary structural groups with heteropolar bonds (AsS 3/2 , SbS 3/2 , SbI 3 , AsI 3 ) and contains a certain amount molecular fragments with homopolar As-As and S-S bonds (As 4 S 4 , S 8 ). It has been established that the crystallization of glasses takes place in several stages. DTA curves of glasses recorded at 3 K/min revealed three exothermic effects. For example, for 40(As 2 S 3 )30(Sb 2 S 3 )30(SbI 3 ) glass temperatures maxima of these effects are equal 341, 398 and 530 K. The first and second effects are less pronounced due to nucleus formation and the formation of nanocrystals in glass matrix. The structure of the phase that arises in the glass matrix at annealing (348 and 398 K) corresponds to the structure of the crystalline SbSI. The formation of triple units SbS 2/2 I occurs as a result of the glass structural relaxation during its softening, which is accompanied by breaking and switching of homopolar and heteropolar chemical bonds in the binary groups that form the structural network of glasses. This process is accompanied by the diffusion of atoms in a distances of interatomic order. The sizes of antimony sulfoiodsde crystalline inclusions increase with annealing temperature and annealing time. The matrixes of the annealed As 2 S 3 -Sb 2 S 3 -SbI 3 system glasses, in which crystalline SbSI inclusions of different dimensions are formed, are determined mainly by As 4 S 4 structural groups linked together by fragments of chains or rings of sulfur atoms. Conclusions. DTA curves, X–ray powder diffraction patterns and Raman spectra of glasses in As 2 S 3 -Sb 2 S 3 -SbI 3 were investigated. The nanoheterogeneous structure of glasses was established. The crystallization of glasses takes place in several stages. The structure of the phase that arises in the glass matrix at annealing corresponds to the structure of crystalline antimony sulfoiodide. The sizes of SbSI crystalline inclusions are dependent on the heat treatment regimes.

The effect of alkali metal ions on crystallization characteristics and luminescent properties of transparent Er3+-doped fluorosilicate glass-ceramics

In current work, transparent fluorosilicate glass-ceramics (GCs) containing NaYF4:Er3+ nanocrystals were successfully prepared by controlled heat treatment process. The thermal properties and crystallization characteristic temperatures were determined by the differential scanning calorimetry (DSC). The X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to confirm the formation of NaYF4 nanocrystals in glass matrix. Energy dispersive spectrometer (EDS) results and Judd-Ofelt (J-O) parameters analysis demonstrated the incorporation of Er3+ into NaYF4 nanocrystals. Intense 2.7 μm luminescence was observed in Er3+-doped GCs upon excitation with a 980 nm laser diode (LD). Furthermore, the effect of different alkali metals (Li+, Na+, K+) on crystallization characteristics and luminescent properties has been studied in detail, which indicates Li+ is the most favorable option for mid-infrared luminescence properties compared with Na+ and K+. The excellent spectroscopic characteristics suggest that the obtained GCs may be promising materials for mid-infrared fiber lasers.

Spectroscopic properties in Er3+-doped germanotellurite glasses and glass ceramics for mid-infrared laser materials

Transparent Er3+-doped germanotellurite glass ceramics (GCs) with variable Te/Ge ratio were prepared by controllable heat-treated process. X-ray diffraction (XRD) and transmission electron microscope (TEM) confirmed the formation of nanocrystals in glass matrix. Raman spectra were used to investigate the evolution of glass structure and photon energy. Fourier transform infrared (FTIR) spectra were introduced to characterize the change of hydroxyl group (OH−) content. Enhanced 2.7 μm emission was achieved from Er3+-doped GCs upon excitation with a 980 nm laser diode (LD), and the influence of GeO2 concentration and heat-treated temperature on the spectroscopic properties were also discussed in detail. It is found that the present Er3+-doped GC possesses large stimulated emission cross section at around 2.7 μm (0.85 × 10−20 cm2). The advantageous spectroscopic characteristics suggest that the obtained GC may be a promising material for mid-infrared fiber lasers.

Enhanced emission and spectroscopic properties in oxyfluoride glass ceramics containing LaOF:Er^3+ nanocrystals

Transparent oxyfluoride glass ceramics (GCs) containing LaOF:Er3+ nanocrystals were synthesized. X-ray diffraction (XRD), Raman spectra and transmission electron microscope (TEM) confirmed the formation of LaOF nanocrystals in glass matrix. Energy dispersive spectrometer (EDS) results and Judd–Ofelt (J-O) intensity parameters demonstrated the incorporation of Er3+ into LaOF nanocrystals. Enhanced 2.7 μm emission was achieved upon excitation with a 980 nm laser diode (LD). Upconversion, near-infrared emissions, and energy transfer mechanisms were studied to elucidate 2.7 μm emission behaviors. The enhanced 2.7 μm emission is most likely ascribed to the incorporation of Er3+ ions into the low phonon energy LaOF nanocrystals. The excellent optical properties of this GC material indicate that it is a promising candidate for mid-infrared fiber lasers.

2.7 μm emissions in Er3+: NaYF4 embedded aluminosilicate glass ceramics

Er3+ doped NaYF4 transparent aluminosilicate glass ceramic was prepared. X-ray diffraction and transmission electron microscopy confirmed the formation of NaYF4 nanocrystals in glass matrix. Absorption spectra and Judd–Ofelt intensity parameters demonstrated the incorporation of Er3+ into NaYF4 nanocrystals. 2.7μm emission due to the transition of 4I11/2→4I13/2 was achieved upon the excitation of a 980nm laser diode. Visible emission spectra, decay curves at 1.53μm and energy transfer mechanism were studied to elucidate 2.7μm luminescent behaviors. Er3+ doped NaYF4 embedded aluminosilicate glass ceramic might provide a new choice for mid-infrared laser and amplifier.

Synthesis and growth of HgI2 nanocrystals in a glass matrix: Heat treatment

Mercury iodide (HgI2) nanocrystals (NCs) were successfully grown in a barium phosphate glass matrix synthesized by fusion. Growth control of HgI2 NCs was investigated by Atomic Force Microscopy (AFM), Optical Absorption (OA), Fluorescence (FL), and X-ray diffraction (XRD). AFM images reveal the formation of HgI2 nanocrystals in host glass matrix. HgI2 NCs growth was evidenced by an OA and FL band red-shift with increasing annealing time. XRD measurements revealed the β crystalline phase of the HgI2 nanocrystals.

Effect of solubility YAG:Nd nanocrystals in glass matrix

The nanocomposites of Y 3Al 5O 12:Nd 3+ (YAG:Nd) incorporated in borate glass were obtained. The single phase of YAG:Nd nanocrystals were obtained by sol–gel method. The borate glass was melted first and ground up then mixed with the nanocrystals. The samples were formed into pellets under pressure and were annealed in temperatures from the range 550–800 °C. The X-ray diffraction patterns show that together with increasing the temperature the contribution of Y 3Al 5O 12 phase decreases and the new YBa 3B 9O 19 phase is observed. The luminescence measurements indicates that the band structures and distribution of band intensities of glass-YAG:Nd nanocrystal composites depends crucially on annealing temperature.

Enhancement of up-conversion luminescence properties in Yb3+/Tm3+/Er3+ tri-doped transparent oxyfluoride tellurite glass ceramics

Optically transparent Er3+/Tm3+/Yb3+ tri-doped oxyfluoride tellurite based nano-crystallized glass ceramics with the batching composition of 73TeO2-15ZnO-7ZnF2-3YF3-1.5YbF3-0.3ErF3-0.2TmF3 (mol%) is prepared by a conventional melting quenching and the subsequent heat treatment processes. The sizes of grown nano-crystals in glass matrix appear to be smaller than 100 nm from the scanning electron microscope measurement. Visible up-conversion luminescence of the as melted glass and glass ceramics is investigated. The three-color up-conversion luminescence intensities by 980-nm pumping are increased significantly due to the heat treatment, and the blue intensity increases with a higher magnitude than other wavelengths after heat treatment.

Synthesis and characterization of Bi2S3 nanocrystals in glass matrix

This is the first evidence for the successful growth of Bi2S3 nanocrystals in glass matrix (SiO2–K2O–Na2O–B2O3–ZnO–TiO2) using the fusion method. Different sizes of nanocrystals in glass matrix were grown by annealing the glass (dispersed with Bi2S3 nucleons) under two different conditions. The glass was annealed between 6 and 48 h at constant temperature 550 °C. The glass was also annealed at the temperature between 550 and 600 °C at constant annealing time 6 h. The Bi2S3 nanocomposite obtained was characterized by optical transmission (OT) spectroscopy and transmission electron microscopy (TEM). OT spectroscopy revealed strong red shift in transmission cut off which indicates increase in particle size of nanocrystals under both the conditions. TEM analysis demonstrated the nanocrystal size in the range of 2–5 nm.

Synthesis and magnetic characterization of Pb1−xMnxS nanocrystals in glass matrix

The synthesis of manganese-doped PbS (Pb1−xMnxS) nanocrystal (NC) dots within a borosilicate glass matrix has been investigated by atomic force microscopy, electron paramagnetic resonance and magnetic measurements. The fusion method was employed in the preparation of the magnetic semiconductor NC dots whereas the measurements performed showed changes in the physical properties of the manganese-doped dots as a result of the Mn2+-incorporation into the hosting PbS crystal structure. Nevertheless, the data indicated that only a small fraction of the nominal Mn-doping was incorporated into the PbS NC dot, in both lower (0.5%) and higher (40%) nominal doping ends. For the lower nominal Mn-doping end (0.5%) we found only about 0.05% actually incorporated into the PbS NC dot whereas about 0.45% appeared dispersed throughout the glass template as isolated paramagnetic centres.

Incorporation of zinc into CdS1?xSex nanocrystals in glass matrix studied by optical spectroscopies

nanocrystals belong to the most extensively studied and well-known objects. They are interesting not only due to the size-dependent effects related to charge carrier spatial confine-ment (see e. g. [1, 2]) and their traditional use as optical cutoff filters, but also due to applications as non-linear optical devices [3 and references therein], and, in particular, as active optical emitters in three-dimensional optical cavities called photonic dots and consisting of micrometer-sized glass spheres [4]. The main parameters, determining the properties of the nanocrystals, are their chemical composition, shape, average size and size dispersion. Near-spherical shape of CdS