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Previous issue date: 2008-04-02 / Neste trabalho de Tese de Doutorado sintetizou-se e caracterizou-se pontos quânticos
(nanocristais) de PbS e Pb1-xMnxS em matrizes vítreas. Obtiveram-se e analizaram-se os
espectros de Absorção Óptica (AO), Ressonância Paramagnética Eletrônica (RPE) e curvas
de Magnetização por SQUID (Superconducting Quantum Interference Device
Magnetometer). As bandas de AO deslocaram-se para comprimentos de ondas menores
com o aumento da concentração de Mn em pontos quânticos de Pb1-xMnxS, que apresentam
“band gap” na região entre 0,41 eV (gap do PbS “bulk”) e 3,5 eV (gap do MnS “bulk”).
Espectros de RPE, correspondentes à transição eletrônica
2
1
2
1 − ↔ + , mostram as seis
linhas hiperfinas dos íons Mn2+ quando incorporados em pontos quânticos de PbS,
apresentando sinais dos tipos SI e SII, característicos de íons Mn2+ incorporados no interior
e na superfície de nanocristal, respectivamente. Curvas de Magnetização obtidas para as
amostras revelam o comportamento paramagnético dos pontos quânticos de Pb1-xMnxS.
Imagens de Microscopia de Força Atômica (MFA), obtidas para a matriz vítrea de
composição 40SiO2 . 30Na2CO3 . 4PbO2 . 1Al2O3 . 25B2O3 (mol%) + 2S (%wt) + xMn
(%wt (Pb)), confirmam o crescimento de nanocristais. Por meio do Modelo de Função
Envelope de Quatro Bandas estimou-se o tamanho médio de pontos quânticos de PbS e Pb1-
xMnxS. As estimativas teóricas para o tamanho médio dos pontos quânticos apresentaram
excelente concordância com as medidas de MFA. ________________________________________________________________________________________ ABSTRACT / In this Thesis PbS and Pb1-xMnxS quantum dots (nanocrystals), hosted in glass matrix, were
synthesized and characterized. Optical absorption (OA), Electron Paramagnetic Resonance
(EPR) and Magnetization curves (SQUID) were used to characterize the as-prepared
nanocrystals. Within the range of 0.41 eV (gap of bulk PbS) to 3.5 eV (gap of bulk MnS)
the OA bands of the Pb1-xMnxS nanocrystals shift toward lower wavelengths as the Mn
content increases. EPR spectra, corresponding to the
2
1
2
1 − ↔ + electronic transition, show
the standard six hyperfine lines of Mn2+ ion when incorporated into PbS nanocrystals, with
SI and SII features labeling Mn2+ ions located at the core and at the surface sites,
respectively. Magnetization curves show the paramagnetic behavior of the as-prepared Pb1-
xMnxS nanocrystals. Atomic Force Microscopic (AFM) images, recorded from the glassbased
samples with composition 40SiO . 30Na2CO3 . 4PbO2 . 1Al2O3 . 25B2O3 (mol%) +
2S (%wt) + xMn (%wt (Pb)), confirm the in-situ growth of nanocrystals. The average sizes
of the PbS and Pb1-xMnxS nanocrystals were estimated using the four-band envelope
function model. The estimated values for the nanocrystals average sizes are in excellent
agreement with the data provided by AFM.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.unb.br:10482/4006 |
| Date | 02 April 2008 |
| Creators | Silva, Ricardo Souza da |
| Contributors | Morais, Paulo César de |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UnB, instname:Universidade de Brasília, instacron:UNB |
| Rights | info:eu-repo/semantics/openAccess |
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