Under diminishing size of semiconductor nanoparticles (quantum dots) they change properties dramatically due to familiar quantum size effects. The species of the lowest possible size corresponding semiconductor crystal lattices (clusters) possess the maximum quantum confined features. They are of interest to follow the transition between molecular properties of few-atomic precursors and nuclei of a solid phase. We consider quantum chemical modeling of cadmium chalcogenide clusters containing tens of atoms. They may be the fragments of bulk lattices and nave arbitrary geometries. Ab initio geometry optimization (at the restricted Hartree-Fock level) together with electronic structure analysis allows to find possible structures of the CdnXm-clusters (X=S,Se,Te) terminating with hydrogen atoms. The clusters considered (up to n=17, m=32) reveal the dramatic variation of properties with size, interband gap is much higher than for the bulk counterparts for all chalcogenides, and simulate well some experimental findings on spectral properties of (CdX)n produced in colloids with organic ligand capping. The results obtained are important as a theoretical base of small semiconductor clusters those do not described within the effective mass approximation and as pathways to discover a growth sequence of these species towards bigger nanoparticles.
Copper incorporation into zeolites by the ion-exchange from Cu(II) solutions followed by different heat treatments results in a production of a number of species. Redistribution among different sites after dehydration, spontaneous and forced reduction, cluster and particle aggregation, etc. can occur, and a final copper state depends on type of zeolite, SiO2/Al2O3 molar ratio and processing conditions. Various species where observed: copper ions Cu2+ and Cu+, small particles and clusters Cun. We concentrate on the appearance of small copper clusters feasible in zeolites with size of cavities those match the cluster size. The clusters were simulated with ab initio quantum chemical calculations in the range of sizes 5 < n < 10 those are probable within zeolites cavities. Experimental data available on optical absorption of the reduced copper in the three types of zeolites can argue on the occurrence of the clusters stabilized within channels under mild reduction conditions while the larger copper nanoparticles appear under the harder reduction. The model calculation proposes some few-atomic copper clusters (Cun) as the candidates to fit the zeolite cavities with correspondence of the calculated absorption bands with the experimental spectra.
Sol-gel glasses containing copper selenide nanoparticles and having absorption band at 1.1?2.2 ?m can be used as saturable absorber passive shutter for Q-switching and mode-locking of the solid-state lasers operating in the wavelength range of 1.0?1.5 ?m. The bleaching relaxation time of the glasses was measured to be 0.46?1.4 ns in dependence on copper selenide stoichiometry.
The silica sol-gel derived glasses co-doped with CuxO and CuxSe nanoparticles and Eu3+ ions have been fabricated. The analysis of luminescence spectra of a series of glasses with different composition allows us to suppose the direct energy transfer between copper oxide nanoparticle and Eu3+ ion. A luminescence signal of europium ions occurs as the result of excitation of the complex active centres (SiO2:Cu2O:Eu3+) in the absorption range of copper oxide.
Binary oxide solid products and glasses in the ZrO2-GeO2 system with the Ge:Zr molar ratio ranged from 1:1 to 3:1 were synthesized from inorganic precursors in aqueous medium by ammonia stimulated hydrolysis and coprecipitation. The latter were formed due to reaction of Zr(IV)+Ge(IV) solution with precipitating agent. The precipitated xerogels covered a color spectrum from white to red, and the color was more intense with increase of GeO2 content in the binary ZrO2-GeO2 composition. DTA, XRD, IR, and XPS were used for examination of crystalline structure and phase transformations in the coprecipitated amorphous xerogels and thermally treated ZrO2-GeO2 products. In samples with excess of germania in the binary ZrO2-GeO2 system both tetrahedral and octahedral coordination of Ge occur, resulting in different crystallization behaviors. In line with the stable ZrGe04 phase with scheelite structure we have established an appearance of new crystalline phase (called X-phase) for thermally treated (1000°C) samples with Ge:Zr = 2:1 and 3:1 rather than the hexagonal GeO2 phase.
Copper nanoparticles were produced within the protonated and alkaline forms of several zeolites by the hydrogen reduction of corresponding Cu-exchanged forms. Variation of zeolite structure, reduction temperature and acidity of zeolites were the main factors influencing metal reducibility and appearance of copper reduced forms. They were detected by means of optical absorption using diffuse reflectance spectroscopy technique. The effect of zeolite type upon the plasmon resonance band associated with the reduced copper clusters was investigated experimentally and discussed with eh Mie theory simulation results. The type of this spectral appearance is associated with size of copper nanoparticles formed as the result of reduction and secondary aggregation and dielectric properties of zeolite micro crystals being a matrix for the nanoparticle stabilization.
Small copper particles within zeolite (mordenite) matrix produced by copper ion reduction were studied. Variation of SiO2/Al2O3 molar ratio of mordenite does not change crystal structure, but results in different ionic properties. A change of SiO2/Al2O3 ratio leads to transformation of the plasmon resonance from a classical peak to a shoulder in the same wavelength range. These features were simulated by the Mie theory, and calculations outlined additional absorption bands those consistent with the experiment.
Nonlinear optical effects in surface oxidized CuFexSy (x equals 1,2, y equals 2,3) nanoparticles incorporated in polymeric film are studied. Surface oxidation of CuFeS2 and CuFe2S3 nanoparticles results in appearance of the additional absorption band with maximum at 1.03 and 1.15 micrometer, respectively. Bleaching of this additional absorption band in CuFe2S3 particles and the induced absorption in all studied samples after picosecond laser excitation take place. An energy level scheme for CuFeS2 and CuFe2S3 nanoparticles with long-lived trap levels in the band gap is proposed and origin of additional absorption is discussed. Characteristic times for career relaxation from conduction band to these trap levels are approximately 25 plus or minus 5 ps for CuFe2S3 and approximately 70 plus or minus 10 ps for CuFeS2 oxidized nanoparticles. The relaxation of electrons from trap levels has characteristic time of more than 500 ps.
Glasses containing nanoparticles of CuInS2 dispersed in a silicate matrix were fabricated. Absorption and luminescence spectra of glasses containing nanocrystals with size of 10 - 70 nm were studied. The possible reasons for the long-wavelength shift of the fundamental absorption edge and the non-chalcopyrite structure of CuInS2 nanoparticles are discussed.
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