Effect of Size Confinement on the Electronic States of CdS Cluster in a Germanium Oxide Matrix

Arai, Toshihiro; Fujumura, Hidehiko; Umezu, Ikuro; Ogawa, Tsutomu; Fujii, Americo

doi:10.1143/jjap.28.484

Cited by 64 publications

(13 citation statements)

References 18 publications

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“…Neste caso, foram utilizados poros umedecidos com géis dentro dos quais reagentes podiam ser difundidos e precipitados, sendo que o tamanho dos poros controlava tanto o tamanho máximo como a distribuição dos nanocristais. 6 Mais tarde, a técnica de co-sputtering foi utilizada para a produção de pontos quânticos de CdSe e Cd x Mn 1-x Se. O crescimento foi realizado por meio de bombardeamento por radiofrequência (sputtering) de um alvo composto pelo material que constituiria o ponto quântico e pela matriz escolhida para confiná-lo.…”

Section: Histórico Do Desenvolvimento Das Sínteses De Pontos Quânticounclassified

O estado da arte da síntese de semicondutores nanocristalinos coloidais

et al. 2010

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, 74, 36301-160 São João del-Rei -MG, Brasil Recebido em 8/11/09; aceito em 21/4/10; publicado na web em 24/8/10 THE STATE OF THE ART IN THE SYNTHESIS OF COLLOIDAL SEMICONDUCTOR NANOCRYSTALS. Colloidal semiconductor nanocrystals, also known as quantum dots, have attracted great attention since they have interesting size-dependent properties due to the quantum confinement effect. These nanoparticles are highly luminescent and have potential applications in different technological areas, including biological labeling, light-emitting diodes and photovoltaic devices. The synthetic methods of semiconductor nanocrystals have progressed in the last 30 years, and several protocols were developed to synthesize monodisperse nanocrystals with good optical properties, different compositions and morphologies. This review describes the main methods used to synthesize nanocrystals in the II-VI and III-V systems, and the recent approaches in this field of research.Keywords: semiconductor nanocrystals; quantum dots; colloidal synthesis. INTRODUÇÃOA síntese de nanocristais, partículas cristalinas com tamanhos de 1 a 100 nm, tem sido o objeto de inúmeros trabalhos científicos no mundo todo, devido às suas intrigantes propriedades ópticas. Dentre os materiais nanométricos, têm-se os semicondutores nanocristalinos coloidais, também chamados de pontos quânticos, os quais apresentam os portadores de carga (buracos e elétrons) em um estado de forte confinamento quântico, o que faz com que estes materiais possuam propriedades ópticas que podem ser alteradas modificando-se apenas o tamanho das nanopartículas. Uma das propriedades ópticas mais interessantes destes nanocristais, do ponto de vista da aplicação tecnológica, é a forte intensidade de luminescência que apresentam, permitindo que sejam utilizados em dispositivos optoeletrônicos, fotovoltaicos e biomédicos, dentre outros. 1,2A Figura 1 apresenta imagens de dispersões coloidais aquosas de nanocristais de telureto de cádmio (CdTe) com diferentes cores de emissão, em função do tamanho das nanopartículas, bem como os espectros de absorção óptica (UV-Vis) e de fotoluminescência (PL) dessas amostras.3 Na Figura 1b é possível observar um deslocamento da banda de absorção óptica fundamental de 480 para 556 nm (red shift), devido à formação de partículas maiores ao longo da evolução da síntese. De maneira semelhante, na Figura 1c, fica evidente um deslocamento das bandas de emissão em direção a comprimentos de ondas maiores, de 507 nm da primeira amostra para 592 nm na última amostra, o que corresponde a uma variação nas cores de emissão, como mostrado na Figura 1a.Os semicondutores nanocristalinos podem ser divididos em diferentes grupos da tabela periódica, tais como II-VI, III-V e IV-VI, sendo que, nesta revisão, são abordados, principalmente, os métodos experimentais de síntese para produção dos semicondutores dos grupos II-VI e III-V, embora esse último grupo seja ainda muito menos estudado. As sínteses destes materiais podem ser realizadas pelo método top-down, que utiliza técnicas ...

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Section: Histórico Do Desenvolvimento Das Sínteses De Pontos Quânticounclassified

O estado da arte da síntese de semicondutores nanocristalinos coloidais

et al. 2010

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“…Especially, the electronic and optical properties of semiconductor nanocrystals embedded in solid matrices such as CuCl in NaCl ͑Refs. 1 and 2͒ and CuCl, CdS, CdSe, CdS x Se 1Ϫx , and Ge in glass [3][4][5][6][7][8][9][10][11][12][13] have been studied in the past decade. Specific attention has been paid [8][9][10][11][12][13] to silicate glasses in which CdS or CdS x Se 1Ϫx nanoparticles are grown by special thermal treatment.…”

Section: Introductionmentioning

confidence: 99%

Acoustic vibrations of semiconductor nanocrystals in doped glasses

et al. 1999

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Polarization-dependent low-frequency off-resonant Raman scattering has been studied from various commercially available filter glass samples, which contain CdS x Se 1Ϫx nanoparticles embedded in a glass matrix. In order to distinguish the confined acoustic phonons from the glass background, the spectra have been compared with those obtained from the base material, which does not contain nanoparticles. Polarized and depolarized scattering from confined acoustic phonons was distinctly resolved near the laser line and overtones of the polarized modes were observed. A theoretical treatment, which establishes a relation between the particle size, the frequencies, and the widths of various phonons, taking into account the matrix influence on the vibrational spectrum and on its damping, is presented. The material-dependent generalized form of this model enables one to use it for any given combination of particle and matrix materials. A good agreement between the experimental and the theoretical results is found. The nanoparticle sizes obtained from Raman scattering agree well with those obtained from transmission electron microscope and anomalous small angle x-ray scattering experiments. ͓S0163-1829͑99͒07231-8͔

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“…14) The experimental results include the size distribution effect and the obtained spectra are the summation of those of the individual nanocrystals. 15) We assume that the lowest excited energies for each annealing time correspond to the absorption peaks indicated by arrows in Fig. 3.…”

Section: Resultsmentioning

confidence: 99%

“…Consequently, the capture cross section of the electrons to the surface states in the small nanocrystal is larger than that in the large one. 15,25) The other explanation is the increase of uniformity of the distribution of the nanocrystal sizes due to the annealing effect. Figure 7 shows a linear relationship between the steepness factor σ and the average radius.…”

Section: Resultsmentioning

confidence: 99%

Photoacoustic Studies of Annealed CdS_xSe_1-x (x = 0.26) Nanocrystals in a Glass Matrix

Shen¹,

Toyoda²

1999

Jpn. J. Appl. Phys.

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Photoacoustic (PA) spectroscopy is applied to study an optical absorption of CdS x Se 1−x (x = 0.26) nanocrystals in a glass matrix annealed at 700 • C for different time durations. As the annealing time increases, a shift of the absorption peak (due to the quantum confinement effect) to lower energy is observed in the PA spectra at room temperatures. The observed absorption peak shifts are used to evaluate the average size of CdS x Se 1−x nanocrystals in terms of a simple model. The average radius increases from 2.3 to 4.7 nm as the annealing time increases from 0 to 120 min. The PA signal intensities plotted in the semilogarithmic scale vary linearly below the fundamental absorption edges in accordance with the Urbach rule for the optical absorption coefficient. The steepness factor (slope of exponential optical absorption) of the PA spectra increases with increasing annealing time. The change of the electronic states by annealing is explained by considering that the contribution of the surface states decreases with the increase of the nanocrystal size.

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Effect of Size Confinement on the Electronic States of CdS Cluster in a Germanium Oxide Matrix

Cited by 64 publications

References 18 publications

O estado da arte da síntese de semicondutores nanocristalinos coloidais

O estado da arte da síntese de semicondutores nanocristalinos coloidais

Acoustic vibrations of semiconductor nanocrystals in doped glasses

Photoacoustic Studies of Annealed CdS_xSe_1-x (x = 0.26) Nanocrystals in a Glass Matrix

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Effect of Size Confinement on the Electronic States of CdS Cluster in a Germanium Oxide Matrix

Cited by 64 publications

References 18 publications

O estado da arte da síntese de semicondutores nanocristalinos coloidais

O estado da arte da síntese de semicondutores nanocristalinos coloidais

Acoustic vibrations of semiconductor nanocrystals in doped glasses

Photoacoustic Studies of Annealed CdSxSe1-x (x = 0.26) Nanocrystals in a Glass Matrix

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Photoacoustic Studies of Annealed CdS_xSe_1-x (x = 0.26) Nanocrystals in a Glass Matrix