Lead sulfide quantum dots in glasses controlled by silver diffusion

Precipitation of PbS quantum dots (QDs) in silicate glasses controlled by Ag⁺ ion diffusion was investigated. Ag⁺ ions penetrated ~ 0.5 μm into the glass when the glass was immersed in the AgNO₃ solution at 80 °C. Ag nano-particles (NPs) and PbS QDs were formed after heat-treatment at temperatures of 420–460 °C for 10 h. PbS QDs in Ag⁺-diffused regions photoluminesced at longer wavelengths than did those in Ag⁺-free regions. This indicates that PbS QDs thus formed in regions containing Ag NPs were larger than those in Ag⁺-free regions and this size difference was confirmed from the transmission electron microscope images. PbS QDs can grow at temperature as low as 420 °C in Ag⁺-diffused regions and this implies that PbS QDs form preferentially using Ag NPs as nucleating agents.     

Optical properties of PbSe quantum dots doped in borosilicate glass

PbSe quantum dots (QDs) were synthesized in borosilicate glass and their optical properties were investigated. The typical quantum confinement effects were clearly observed from the absorption when the average radii of the QDs changed from 1.7 to 3.1 nm. Photoluminescence from PbSe QDs was achieved in 1.1–2.2 μm wavelength region that covers the entire fiber-optic telecommunication window. Borosilicate glasses containing controlled size of PbSe QDs provide potentials for the fiber-optic amplifiers.     

Photoluminescence of PbS quantum dots embedded in glasses

Optical properties and photoluminescence of PbS quantum dots (QDs) embedded in glasses were investigated. Formation and radius of PbS QDs were carefully controlled though heat-treatment and modification of host glass composition. Heat-treatment conditions for precipitation of 3–10 nm radius QDs for the tunable photoluminescence in the 1–2 μm wavelength range were identified. Glasses doped with PbS QDs provide potential as robust materials for broadband fiber-optic amplifiers.     

Optical properties of novel PbS and PbSe quantum-dot-doped alumino-alkali-silicate glasses

Lead sulfide PbS and lead selenide PbSe quantum dots (QDs) were synthesized in novel alumino-alkali-silicate glass. The synthesis of the nanocrystals was stabilized by introduction of two alkaline components. The presence of crystalline phase was confirmed by X-ray diffraction analysis, transmission electron microscopy and optical spectroscopy. For PbS (PbSe) QD-doped glass, the position of the 1S–1S excitonic absorption peak can be managed in the spectral range of 1.5–2.1 μm (for PbS) or 1.8–2.2 μm (for PbSe) by appropriate heat‐treatment mode. The corresponding QD average diameter was found to be 5.8–9.7 nm (for PbS) and 7.5–9.5 nm (for PbSe). The influence of the secondary heat-treatment at the temperatures of 490–525 °C on the PbS QD growth in the glass matrix initially treated at 480 °C was studied in details. The photoluminescence of the PbS-QD-doped glass was observed, it was referred to the radiative recombination of the excitons from the 1S–1S state. The possibility to obtaining narrow 1S–1S absorption lines at the wavelengths longer than 2 μm is discussed.     

Structural peculiarities, and electrical and optical properties of 70TeO2·30PbCl2 glasses doped with Pr, prepared in Pt or Au crucibles

The influence of crucibles (Au or Pt) on the structure, electrical, dielectric and optical properties of 70TeO₂·30PbCl₂ glasses doped with Pr³⁺ added as a metal, chloride, or oxide, in concentrations of 500–1500 wt-ppm, is reported. The dc conductivity of ‘pure’ glasses prepared in Au crucibles is two orders of magnitude higher than that of those prepared in Pt crucibles. Upon doping, the dc conductivity of glasses prepared in Pt and Au crucibles increases or decreases, respectively. The static relative permittivity is equal to 33 ± 2. In the range of 640–700 nm, six photoluminescence (PL) peaks were observed, at 641.5, 647.1, 652.4, 660.8, 662.9, and 664.5 nm. In the range of 200–1200 cm⁻¹, seven Raman scattering (RS) peaks were observed at 184, 217, 321, 468, 654, 735 cm⁻¹, and a small peak at 650 cm⁻¹. Both spectra were deconvoluted using symmetrical Gaussian functions. Relative intensities of PL and RS bands depend on the concentration and chemical form of Pr³⁺ and on the material of the crucible. However, positions of these bands are independent of these conditions.     

Self-alignment of self-assembled InAs quantum dots

The lateral self-alignment properties of self-assembled InAs quantum dots (QDs) on a conventional GaAs (1 0 0) substrate by molecular beam epitaxy were investigated. The shape and optical properties of QDs were investigated by atomic force microscopy, transmission electron microscope, and photoluminescence (PL). Attempts were made to grow InAs-QDs using the In-interruption growth technique, in which the In flux was periodically interrupted. QDs grown without using the In-interruption growth technique were grown randomly on all regions. On the other hand, in the case of QDs grown using the In-interruption growth technique, QDs were self-aligned at the boundary between bright and dark regions, the PL intensity was increased and the PL peak position of QDs were red-shifted to 1300 nm. This represent a new technique for growing self-aligned QDs because no extra processing such as electron-beam lithography, V-grooves and surface modification by scanning tunneling microscopy is needed, and aligned QDs can be grown in situ on conventional GaAs substrates.     

Optical properties of chalcogenide multilayer deposited on Au layer

The chalcogenide multilayers were prepared as dielectric mirrors having the first order stop bands in the near infrared region 1.55 μm. The 7.5 layer pairs of the alternating amorphous Sb–Se and As–S layers were deposited on glass substrates using a conventional thermal evaporation method. To center the stop bands of the 15-layer dielectric mirrors at 1.55 μm, the layer thicknesses 117 nm for Sb–Se and 169 nm for As–S single layers were calculated from the quarter wave stack condition. The optical reflection and transmission spectra of the prepared mirrors were measured using a UV/VIS/NIR and FT-IR spectroscopy at the ambient and elevated temperatures. The optical reflection of the annealed 15-layer chalcogenide mirror was found higher than 99% in the range of 1440–1600 nm. As the 200 nm thick gold layer was added between the substrate and the chalcogenide mirror, the stop band of the annealed Au/multilayer system broadened to 1360–1740 nm simultaneously with an appearance of the 15% transmission peak at 1.55 μm. A preparation of similar metal/multilayer systems is one of the possible ways how to design the dielectric filters for near infrared region exploiting the good optical quality of the chalcogenide films and their simple deposition.     

New photoluminophore nanocomposite based on organic compound with Eu ions and copolymer styrene-butylmethacrilate

New nanocomposite (NC) material on the base of thenoyltrifluoroacetone (TTA) coordinated with trivalent europium ions and structured with phenantroline (Eu(TTA)₃Phen) and copolymer from styrene and butylmethacrylate (1:1) (SBMA) was prepared. The visible photoluminescence spectra of composites excited with N₂-laser (λ = 0.337 μm) at room and T = 78 K temperatures were studied. For the Eu(TTA)₃Phen/SBMA nanocomposite material emission bands located at 578, 590, 612, 675 and 705 nm can be attributed to the spin forbidden f–f transitions ⁵D₀ → ⁷F_i (i = 0,1,2,3 and 4), respectively. The more intensive luminescence band situated at 612 nm with the half width of 3 nm is connected to the Eu³⁺ ion electronic transition ⁵D₀ → ⁷F₂. It was shown that the maximum intensity of photoluminescence occurs at the concentration of 15% of the Eu(TTA)₃Phen in the SBMA polymer matrix.     

Fluorescence of copper, manganese and antimony ions in phosphate glass host

The paper presents a study based on luminescence characteristics of phosphate glasses containing Cu²⁺, Mn⁴⁺ and Sb³⁺. The glass samples obtained by a wet chemical route belong to Li₂O–BaO–Al₂O₃–La₂O₃–P₂O₅ oxide system. The oxide composition of the glass samples is calculated to obtain a vitreous network composed of metaphosphate chains bonded by modifier ions (Li⁺, Ba²⁺ and La³⁺) and fluorescent ions. The absorption spectra of the samples were acquired in the UV domain in order to establish the excitation wavelength for each fluorescent ion. The absorption peaks of Sb³⁺ ion are ranged at 285 nm and 250 nm, Mn²⁺ ion at 280 nm and 365 nm, Cu²⁺ ion at 295 nm and 313 nm. The luminescence peaks of Cu²⁺, Mn⁴⁺ and Sb³⁺ ions are found in the visible domain at different wavelengths, depending on the oxidation state and coordination symmetry of each fluorescent ion. The fluorescence of Sb³⁺ ion has a strong signal at 450 nm and a weak one at 465 nm, Mn²⁺ ion shows a fluorescence peak at 600 nm and the pair Cu²⁺/Cu⁺ ions reveals a fluorescence emission at 460 nm.     

Bi-doped glass optical fibers: Is it a new breakthrough in laser materials?

It has been shown recently, that Bi-doped glass optical fibers are a very promising active laser medium. Luminescence of Bi-doped glasses takes place in a spectral region of 1150–1500 nm, where no efficient fiber lasers (or any other efficient lasers) exist. The glasses have very broad luminescence bands (200–400 nm) and long lifetime (200–700 μs). The Bi absorption bands are situated in a spectral region of 500–1100 nm where long-lived high-brightness laser diodes developed for the pumping of lasers and amplifiers are available. Besides, strong luminescence has been observed in a variety of glass compositions. In this paper the recent results on the new laser material – Bi-doped glasses and optical fibers are reviewed. First, luminescence properties of various Bi-doped glasses are discussed. Then we describe the Bi-doped silica-based optical fiber fabrication and the absorption and luminescence properties of the fibers. At last some results on Bi-doped fiber lasers and their applications are presented.     

Photoconductive organic materials based on N-vinylcarbazole copolymers with higher alkenes as recording media in photonics

With the purpose to obtain novel photoconductive organic materials with improved complex of physical–mechanical properties and high sensitivity value, the possibility of N-vinylcarbazole copolymerization with higher alkenes was studied.The deposited films were 1.0–2.0 pm thin after drying in vacuum. The photosensitivity of the copolymer films is one order of magnitude greater than other carbazole containing copolymers. The investigation of spectral sensitivity was realized. Photosensitivity reaches its maximal value in 400–800 nm wave band.A photothermoplastic information registration medium was developed using synthesized copolymers. On the prepared photothermoplastic film, were recorded diffraction gratings with diffractional efficiency of 8–10% and resolution of 1000 mm⁻¹, using electrophotographic method. Photographical sensitivity of obtained films allows real time (1–3 s) photographical and holographic image recording.     

High-density carrier dynamics in Ge/Si quantum dots studied by time-resolved photoluminescence spectroscopy

We studied the temperature dependence of high-density carrier dynamics in as-grown and thermally annealed Ge quantum dots (QDs) in silicon crystals. In as-grown and thermally annealed samples, photoluminescence (PL) intensity exhibited a power-law dependence on the excitation intensity and its power-law index was ~ 0.7 at low temperatures. With increasing measurement temperature, PL intensity decreased and the index of the power-law function increased up to ~ 1.5, in which carrier recombination dynamics is dominated by a single carrier trapping. Moreover, in thermally annealed QDs, the index of the power law increased more rapidly than as-grown QDs, suggesting that the carrier recombination dynamics drastically changed in thermally annealed QDs. Effects of Ge/Si interface on high-density carrier recombination process are discussed.     

Peculiarities of photoluminescence excited by 157 nm wavelength F2 excimer laser in fused and unfused silicon dioxide

Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F₂ excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperbolic functions. The UV band of the unfused material is characterized by decay with exponential time constant τ  4.5 ns and hyperbolic function t⁻ⁿ, where n = 1.5 ± 0.4. For the blue band the hyperbolic decay kinetics with n  1.5 extends to several milliseconds, gradually transforming to the exponential one with τ = 11 ± 0.5 ms. In fused glass relative contribution of the fast component to the UV band is small whereas for the blue one it is great, that allows one to more accurately determine the hyperbolic law factor n = 1.1 ± 0.1 typical for tunneling recombination. Simultaneous intracenter and recombination luminescence, the later occurring with the participation of laser radiation induced defects, add particular features to the decay kinetics. Spectra of the above luminescence processes are different. A less sharp position of bands is associated with the recombination luminescence. The origin of the observed PL features we attribute to the presence of oxygen deficient centers in glass network in the form of twofold coordinated silicon. Such centers being affected by network irregularities can be responsible for the recombination PL component. A great variety of network irregularities is responsible for centers’ structural inequivalence, which causes a non-uniform broadening of PL spectral and kinetic parameters.     

Synthesis via an organic molten salt solvent route and characterization of PbS nanocrystals

In this paper, four petals flowers‐like and quasi sphere‐like PbS nanostructures were successfully synthesized by an environment friendly organic molten salt solvent (OMSS) route at 200 °C, with different sulfur sources, e.g. thiourea and sodium thiosulfate, respectively. The as‐synthesized products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV–vis absorption spectrum and photoluminescence (PL) spectrum, respectively. It was shown that four petals flowers‐like and quasi sphere‐like PbS nanocrystals were formed. It was also demonstrated that the morphologies of PbS nanocrystals were significantly influenced by different sulfur sources. The ultraviolet‐visible absorption peaks of PbS nanocrystals exhibited a large blue‐shift and the luminescence spectra had strong and broad emission bands centered at 488 nm and 492 nm. The possible formation mechanisms of the PbS nanostructures were discussed. The organic molten salt solvent (OMSS) method is preferable for synthesizing high‐quality PbS nanocrystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of IV–VI quantum dots embedded in glass: Size-effects

Measurements of the photoluminescence (PL), micro-PL, spatially-resolved PL, optical absorption and atomic force microscopy (AFM) of PbS and PbSe quantum dots (QDs) embedded in oxide glass matrix, were carried out. It was found that the energy gaps of the QDs showed pronounced anomalous temperature dependences. Their temperature coefficients depended strongly upon the size and shape of the QDs, and surface and/or confined phonon modes. In addition, the energy-dependent transfer rate of excitons from smaller to larger dots via electronic coupling was observed. It was predicted that further improvements in size selectivity, luminescence quantum yield, and well-controlled growth would enable highly efficient inter-dot energy transfer.     

Self-assembled InAs quantum dots with two different matrix materials

The effects of matrix materials on the structural and optical properties of self-assembled InAs quantum dots (QDs) grown by a molecular beam epitaxy were investigated by atomic force microscopy, cross-sectional transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. Cross-sectional TEM image indicated that the average lateral size and height of InAs QDs in a GaAs matrix on a GaAs substrate were 20.5 and 5.0 nm, respectively, which showed the PL peak position of 1.19 μm at room temperature. The average lateral size and height of InAs QDs buried in an InAlGaAs matrix on InP were 26.5 and 3.0 nm, respectively. The PL peak position for InP-based InAs QDs was around 1.55 μm at room temperature. If we only consider the size quantization effects, the difference in PL peak position between two QD systems with different matrices may be too large. The large difference in peak position can be mainly related to the QD size as well as the strain between the QDs and the matrix materials. The intermixing between the QDs and the matrix materials can partially change the In composition of QDs, resulting in the modification of the optical properties.     

Optical and structural properties of Ge–Se bulk glasses and Ag–Ge–Se thin films

The optical and structural properties of Ge₂₀Se₈₀, Ge₂₅Se₇₅ and Ge₃₀Se₇₀ bulk glasses and Ag_x(Ge_0.20Se_0.80)_100−x thin films, where x = 0, 6, 11, 16, 20 and 23 at.% were studied. All samples were confirmed as amorphous according to XRD. The Raman spectra showed increase in 260 cm⁻¹ and 237 cm⁻¹ and decrease in 198 cm⁻¹ and 216 cm⁻¹ bands with different Se content in the bulk samples. The optical bandgap energy of bulk samples decreased (2.17–2.08 eV) and refractive index increased (2.389–2.426 at 1550 nm) with increasing Se content in bulk glasses. The Ge₂₀Se₈₀ thin films were prepared by vacuum thermal evaporation from Ge₃₀Se₇₀ bulk glasses. The Raman spectra of the films showed that peaks at 260 cm⁻¹ and 216 cm⁻¹ decreased their intensities with increasing Ag content in the thin films. The significant red shift of bandgap energy occurred upon different Ag content. The optically induced dissolution and diffusion resulted in graded refractive index profile along the film thickness caused by different Ag concentration. The refractive index increased from the substrate side to the top of thin films. The graded profile was getting more uniform with increasing content of silver in the thin film.     

Correlation between the luminescence properties and the surface structures of submicron silica particles

We investigated the correlation between the luminescence properties and the surface structures of submicron silica particles prepared by the Stöber method. After annealing in a non-oxidizing atmosphere, the submicron-sized silica particles show a broad photoluminescence (PL) band at 500–540 nm by excitation at an ultraviolet wavelengths (254 and 365 nm), and the one at the 600 nm by excitation an Ar⁺ laser (488 nm). The PL appeared to result from the removal of impurities and subsequent formation of several luminescent structures on the internal surface of the primary particles by thermal annealing.     

Preparation of PbS nano‐microcrystals with different morphologies and their optical properties

PbS nano‐microcrystals were prepared from Pb(OAc)₂·3H₂O and sulfur in a solution without any surfactant using the solvothermal process. Different morphologies, mainly including polyhedron microcrystals and sphere‐like assemblies, were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). PbS nano‐microcrystals with cubic crystal structure were detected using X‐ray diffraction (XRD), electron diffraction (ED) and high resolution transmission electron micrograph (HRTEM) techniques. The optical properties were investigated by ultraviolet‐visible (UV‐vis) spectroscopy, and photoluminescence spectroscopy (PL). The UV‐vis absorption peaks of PbS exhibited a large blue‐shift and the PL spectra had a strong and broad emission bands centered at 408 nm. The crystal growth mechanism of PbS was also discussed.     

Nonlinear optical properties of PbS quantum dots in boro-silicate glass

PbS quantum dots synthesis in boro-silicate glass is presented. Absorption bleaching of PbS quantum dots of ≈4 and ≈7 nm in diameter dispersed in this glass has been studied. Bleaching relaxation time of 20–30 ps, absorption saturation fluence of ≈5 mJ/cm² and ground-state absorption cross-section of 2 ÷ 6 × 10⁻¹⁷ cm² at the wavelengths corresponding to the first excitonic absorption band maxima are measured.