Lead Chalcogenide Quantum Dot-Doped Glasses for Photonic Devices

Tunable absorption and photoluminescence (PL) of lead chalcogenide quantum dots (QDs) doped in glasses due to the quantum confinements effect have been actively investigated for application as saturable absorbers, laser sources, and fiber-optic amplifiers. Optical properties of QDs have been carefully monitored by controlling their sizes through heat treatment and rare-earth ion doping. Two- and three-dimensional precipitation of lead chalcogenide QDs were also realized using silver ion exchange and femtosecond laser irradiation in combination with thermal treatment. Prototypes of microstructured single-mode fibers and tapered fiber amplifiers containing QDs proved potentials of these materials for fiber-optic amplifiers application. Further research works on QD-doped solid core fibers, surface passivation of quantum dots and their application for the mid-infrared optical devices are necessary.     

Fluorophosphate Glasses with Quantum Dots Based on Lead Sulfide

The specific features in the formation of IV–VI (PbS) quantum dots in a vitreous fluorophosphate matrix are investigated by X-ray microanalysis, high-resolution scanning transmission electron microscopy (STEM), high-resolution X-ray diffraction, and optical absorption spectroscopy. A complete characterization of the nanocrystals grown (their sizes and morphology) in the glass is performed on the basis of the results obtained. It is demonstrated that spherical PbS nanocrystals with a cubic lattice of the NaCl type are formed in fluorophosphate glasses synthesized. The nanocrystals are uniformly distributed over the matrix bulk and are characterized by a narrow size distribution (R/R 7%) in the studied size range R 2.0–15 nm, which corresponds to strong quantum confinement.     

Fluorophosphate Glasses Containing PbSe Quantum Dots

The specific features in the formation of IV–VI (PbSe) quantum dots in a vitreous fluorophosphate matrix are investigated by X-ray microanalysis, high-resolution scanning transmission electron microscopy (STEM), high-resolution X-ray diffraction, and optical absorption spectroscopy. A complete characterization of the quantum dots grown (their sizes, morphology, and distributions over the matrix bulk and sizes) in the glass is performed on the basis of the results obtained. The inference is made that spherical PbSe nanocrystals with a cubic lattice of the NaCl type are formed in fluorophosphate glasses. The nanocrystals are uniformly distributed over the matrix bulk and are characterized by a narrow size distribution (R/R 7%) in the studied size range R 1.8–10 nm, which corresponds to strong quantum confinement. It is noted that the mechanism of the quantum-dot growth in the glasses under consideration differs from the mechanisms studied earlier in glasses of silicate systems.     

Crystallization Behaviors of PbSe Quantum Dots in Silicate Glasses

This study, composed of three parts, aims at studying the crystallization behaviors of PbSe quantum dots (QDs) in silicate host glasses. Firstly, due to the importance of the choice of base glass for the QDs' crystallization, the selection of base glass compositions, the glass fragility, and glass formation ability (GFA) are discussed in details, and the results show that the selected glass compositions have an intermediate fragility and accordingly an intermediate glass transition temperature range among a wide variety of inorganic glass systems together with a good GFA/glass stability (GS). Thus, this base glass is suitable as the host glass in which PbSe QDs crystallize. Secondly, the experimental results on PbSe QDs' crystallizations are presented, and the results show that PbSe QDs can precipitate from silicate glasses favorably with no other chemical compounds precipitation, and the optimized temperature for PbSe QDs crystallization is 600°C. Lastly, the classical nucleation theory is used to analyze the PbSe QD crystallization behaviors in host glasses. The steady‐state nucleation rates and the growth rates of PbSe QDs as well as the time–temperature transformation (TTT) curves are calculated. The results indicate that the free surface energy between the PbSe nuclei and the host glass has great influence on the nucleation rates of PbSe QDs, while it has less effect on the growth rates of PbSe QDs; the crystallization behaviors of PbSe QDs with different volume fractions can be described well by the TTT curves while keeping the dimensionless empirical constant, α, unchanged for one certain curve.     

Band Gap and Diameter Modulation of Quantum Dots in Glasses

Modulation of the band gap energy and diameter of quantum dots (QDs) formed in glasses is important to achieve the optimized performance for applications as infrared light sources, lasers, saturable absorbers, etc. Absorption and photoluminescence of PbS QDs were extended into mid-infrared wavelength range in glasses containing small amount of lead but oversaturated with sulfur. Dual-band photoluminescence of PbSe QDs was prepared in oxyfluoride glass-ceramics containing BaF₂ nanocrystals. By introducing SnO in the glasses, alloyed Pb_1-xSn_xSe QDs with smaller band gap energies were formed in glasses, and mid-infrared photoluminescence of Pb_1-xSn_xSe QDs at ~2570 nm in wavelength was achieved.     

硫系玻璃中光诱导各向异性效应的研究

详细讨论了硫系玻璃中光诱导各向异性研究的历史、测量方法及其动力学特征和硫系玻璃中光诱导各向异性的来源和模型及其应用。     

Precipitation and Optical Properties of CsPbBr3 Quantum Dots in Phosphate Glasses

CsPbBr₃ quantum dots were precipitated in phosphate glasses through heat treatment. Controlled formation of CsPbBr₃ quantum dots was realized by adjustment of heat‐treatment conditions. Absorption and photoluminescence spectra of CsPbBr₃ quantum dots were tuned from 432 to 521 nm. Upon ultraviolet or blue light excitation, efficient photoluminescence from these CsPbBr₃ quantum dots doped phosphate glasses was observed.     

Phase Separation in Chalcogenide Glasses: The System AgAsSSe

We report on visualization of a phase separation in Ag_x(As_0.33S_0.67)_100−x and Ag_x(As_0.33S_0.335Se_0.335)_100−x chalcogenide glasses by means of atomic force microscopy (AFM). Sufficient topographical contrast (~20 nm) was achieved by selective polishing of a phase-separated sample (Ag-poor, Ag-rich regions) and phase separation occurred within 0.5–20 at.% Ag and 2–18 at.% Ag in Ag_x(As_0.33S_0.67)_100−x and Ag_x(As_0.33S_0.335Se_0.335)_100−x systems, respectively. Homogenous regions were observed below and above the phase separation lower and upper limits. Direct comparison of scanning electron microscopy and atomic force microscopy sensitivity of phase separation detection is shown. In addition, concentration of silver in particular phases of AgAsS system was evaluated by NanoSIMS (secondary ion mass spectroscopy) and very similar concentration of silver was detected in the phases at boundaries of immiscibility region.     

Photoinduced Fluidity and Viscoelasticity in Chalcogenide Glasses

This work is an attempt to apply conventional mechanical testing to characterize the photoinduced viscoelastic behavior of chalcogenide glasses. Creep or relaxation-recovery experiments are usually performed to characterize the delayed elastic contribution to deformation, during thermally activated flow. In this article, relaxation-recovery is used to characterize delayed elasticity under irradiation condition and to investigate the influence of the photon irradiation on the viscoelastic behavior. It is showed that thermally activated processes and photoinduced ones are decoupled. The viscoplastic deformation under irradiation is the sum of thermally activated and photoinduced processes. As soon as the irradiation ceases, chalcogenide glasses behave exactly as if they had never been irradiated. The photoinduced viscoelastic behavior seems to be solely due to transient photoinduced structural defects.     

Influence of Intermediate ZnO on the Crystallization of PbSe Quantum Dots in Silicate Glasses

Glasses containing PbSe quantum dots have important prospective applications in the area of near infrared optoelectronic devices. ZnO plays an important but complicated role in the preparation of quantum dot glass. We gave reasonable elaborations on the color changes of the as‐prepared and annealed glasses containing PbSe quantum dots. The as‐prepared glasses presenting nearly black to transparent straw‐yellow colors with rising ZnO content can be understood in terms of the conversion between PbSe and ZnSe; the colors of all annealed glasses turning very black can be well explained through thermodynamic calculations with the Gibbs–Helmho1tz equation. Next, according to the results of X‐ray diffraction, transmission electron microscopy and optical measurements, the sample with an introduction of 9.4 wt.% ZnO possesses a maximum degree of crystallization and the best optical properties among all samples, which suggests the host glass with addition of 9.4 ± 1 wt.% ZnO is optimum for crystallization of PbSe quantum dots. Finally, we employed classical nucleation theory to quantitatively calculate the nucleation rates and growth rates of PbSe quantum dots, and found that with the growing ZnO content in host glass, the nucleation rate decreases, whereas the growth rate of PbSe quantum dot increases gradually.     

Plasmon‐Assisted Precipitation of PbS Quantum Dots in Glasses Containing Ag Nanoparticles

PbS QDs of ~ 5nm diameter were precipitated in glasses containing Ag nanoparticles after 3 min of 1.5‐W continuous‐wave laser illumination at λ = 532 nm. Photoluminescence spectra of the PbS QDs recorded in the 1.3~1.6 μm wavelength region revealed conversion of photon energy to thermal energy by surface plasmon resonance. Laser‐assisted local heating around Ag NPs can provide a new method to control the spatial distribution of QDs in glasses.     

Direct Imaging of the Distribution of Nd3+ Ions in Glasses Containing PbS Quantum Dots

The influence of Nd³⁺ ions was investigated on the precipitation and optical properties of PbS quantum dots (QDs) inside silicate glasses. The diameters of the PbS QDs decreased as the concentration of Nd³⁺ in the glass increased as evidenced by blue shifts in the absorption and photoluminescence spectra. Electron energy loss spectroscopy shows that Nd³⁺ ions exist preferentially inside the PbS nanocrystals rather than in the glass matrix. We postulate that Nd–O clusters are preserved during heat treatment and serve as nucleation sites for PbS crystals. No change in the local bonding scheme of the Nd³⁺ ions was observed following heat treatment.     

Microseparation in Lead Borate Glasses

The microstructure of a series of lead borate glasses was studied by electron microscopy and small-angle X-ray scattering techniques. Although the glasses were optically homogeneous, microheterogeneities of the order of 2000 to 3000 A were detected in glasses with compositions near the region of two-liquid stability. The size of these heterogeneities increased as the composition approached the region of immiscibility.     

Concentration Quenching of Luminescence of Rare-Earth Ions in Chalcogenide Glasses

An equation describing the concentration dependences of the luminescence of rare-earth ions in different media is proposed. This equation makes it possible to evaluate the degree of homogeneity of rare-earth ion distribution over the matrix with the use of a numerical parameter, namely, the segregation factor.     

Role of Nitrogen in the Crystallization of Silicon Nitride-Doped Chalcogenide Glasses

Glasses in the Ge-S, Ge-As-Se, and Ge-As-Se-Te systems, doped with Si₃N₄, were melted after sealing under reduced pressure, and their crystallization behavior was examined using differential thermal analysis/differential scanning calorimetry and X-ray diffractometry. The effect of Si₃N₄ doping on the suppression of the crystallization of chalcogenide glasses was confirmed for all three systems and is attributed to the increased crosslinking upon substitution of the chalcogens by nitrogen atoms, presumably forming structural units that are similar to Ge₃N₄.     

粉体热压法制备As2Se3硫系玻璃研究

本研究尝试将As₂Se₃红外硫系透镜生产过程中产生的块体玻璃废料进行回收利用,首先将清洗后的块体玻璃废料球磨成粉体,然后采用粉体热压技术实现高光学质量As₂Se₃玻璃片的制备。研究了粉体粒度、热压参数对制备的As₂Se₃玻璃光学性能的影响,对比了粉体热压法和熔融淬冷法制备的As₂Se₃玻璃的性能,评估了通过粉体热压途径制备红外硫系玻璃的可行性。结果表明:随着球磨时间的延长,As₂Se₃玻璃粉体的平均颗粒尺寸逐渐减小,且颗粒尺寸的分布趋于更加均匀;使用平均颗粒尺寸为9.7 μm的粉体(球磨10 min),在压力为40 MPa、热压温度为250 ℃、热压时间为10 min的条件下获得的热压玻璃的致密度达到99.8%,其折射率与熔融淬冷法制备的玻璃的折射率接近(在10 μm波长的折射率差仅为0.003),在10 μm波长的透过率达61%(理论透过率为63.7%)。通过进一步提高玻璃粉体的纯度和尺寸均匀性,有望制备出与熔融淬冷法制备的玻璃性能相当的热压玻璃。     

若干硫系玻璃黏度变化速率的结构起源探索

用熔融淬冷法制备Ge₃₃As₁₂Se₅₅、Ge₂₂As₂₀Se₅₈、Ge₁₀As₄₀Se₅₀、As₄₀Se₆₀、Se硫系玻璃,采用流变仪测试样品黏弹状态的黏度,计算各样品黏度的Vogel-Fulcher-Tammann 方程和黏度变化速率(即料性)。结合拉曼光谱,根据玻璃微观结构对料性的影响规律进行系统分析。发现随着Ge_xAs_ySe_100-x-y硫系玻璃中Ge、As含量的增加,玻璃黏度随温度的变化速率先降低再升高,料性先变长后变短。在平均配位数=2~2.6时,随着平均配位数的增大,组成玻璃的原子之间的平均键能和网络结构稳定性逐渐变大,黏度变化速率降低,料性变长;在=2.6~2.78时,随着网络结构中As-As/Ge-Ge缺陷键的出现,玻璃网络结构的稳定性降低,玻璃黏度的变化速率加快,料性变短。     

Anionic Conduction in Lead Halosilicate Glasses

Electrical conductivity due to halide ions has been measured for the glasses in the system 30SiO₂· (70 − x )PbO · x PbX₂ (0 < x < 17.2 mol%; X = F, Cl). The conductivity increases with x by several orders of magnitude for both series of glasses. The contribution of principal factors to the conductivity has been examined. The analysis of the activation energy on the basis of the Anderson-Stuart model shows that the strain energy is a predominant term in the Cl glasses, while both the strain energy and the electrostatic energy have a comparable contribution in the F glasses. The decrease in the activation energy with increasing PbX₂ content is related to the decrease in the shear modulus for the Cl glasses and to the increase in the permittivity for the F glasses.     

CdTe量子点的水相制备

在水相中以巯基丙酸作为稳定剂,合成出具有不同荧光发射波长的CdTe量子点（QDs）,利用紫外吸收光谱（UV）、荧光光谱（FS）以及透射电子显微镜（TEM）对CdTeQDs进行了表征。研究了反应温度及pH值对所制备的CdTeQDs光学性质的影响。实验结果表明,合成CdTeQDs的最佳温度为96℃,pH值为10,且随着时间的增加量子点的粒径增大。