Engineering of semiconductor nanocrystals and metal Ions in amorphous materials

Semiconductor nanocrystals (NCs), metal ions containing glass based materials have applications in design engineering, and may solve many technological problems. P2O5 based glasses are an important class of materials for several applications, especially for high power laser. Recently, the construction of semiconductor NCs-based phosphate glass materials has been shown to be of high importance for various applications, like in photovoltaics, LEDs, lasers and spintronics. The major challenges are the intentional insertion of dopants into semiconductor NCs aiming expanding their intrinsic functionalities and the scalable incorporation of NCs into host free of hydroxyl and organic species for stabilizing and integrating their performances. On the other hand, the low refractive index of phosphate glass can be adjusted by the addition of a high index of TeO2 content. These hybrid materials fulfil the requirement of refractive index contrast for chromatic dispersion control and are useful for the design of photonic materials. The thesis focus on the design of ZnNiTe semiconductors in transparent phosphate glass-ceramics, and the effect of TeO2 environment in Nd3+ doped phosphate glass for optoelectronic and solid-state laser applications. The structural features of these materials have been determined by XRD, FT-IR and Raman spectroscopic techniques. Optical properties were characterized by using UV-Vis-NIR absorption and fluorescence spectroscopic techniques. The findings were used to estimate crystal field interaction parameters, coordinate state of Ni2+ ions, Judd-Ofelt intensity parameters for Nd3+ ions and radiative properties of metal ions in glasses. Thermal diffusivity (D) and thermal conductivity (K) of ZnNiTe NCs in glasses were determined using thermal lens (TL) and thermal relaxation (TR) techniques. The results revealed that the behaviors of D and K for the studied samples are similar. Nonlinear optical properties of ZnNiTe NCs glasses were also studied using Z-scan technique. The nonlinear refractive property is observed only in the sample containing 5% Ni. Other samples with 1.0% to 10% of Ni content presented nonlinear absorption nature. This suggests that the absorption coefficient, β does not change significantly with the wavelength, but increase with Ni concentration, with confinement effects and two-photon absorption (TPA).Nanocristais semicondutores (NCs), íons metálicos contidos em materiais à base de vidro, podem ter aplicações em projetos de engenharia e resolver muitos problemas tecnológicos. Composições de vidro à base de P2O5 constituem uma classe importante de materiais para diversas aplicações, especialmente para aplicações de laser de alta potência. Recentemente, a produção de materiais de vidro fosfato à base de NCs semicondutores tem se mostrado de fundamental importância para aplicações em várias áreas tais como, fotovoltaica, LEDs, lasers e spintrônica. Os principais desafios são a inserção intencional de dopantes nos NCs semicondutores de forma a expandir suas funcionalidades intrínsecas e a incorporação de NCs em hospedeiros livres de hidroxila e espécies orgânicas para estabilizar e integrar seus desempenhos. Por outro lado, o índice de refração pequeno dos vidros fosfato pode ser ajustado pela adição de TeO2 que possui alto índice de refração, permitindo assim o controle da dispersão cromática que é útil para projetos de materiais fotônicos. O foco da tese é a caracterização de semicondutores ZnNiTe crescidos em materiais vitro-cerâmicos transparentes a base de fosfato e o efeito de TeO2 em vidro fosfatos dopados com Nd3+ para aplicações optoeletrônicas e de lasers de estado sólido. As características estruturais desses materiais foram determinadas por técnicas espectroscópicas de XRD, FT-IR e Raman. As propriedades ópticas foram caracterizadas pelo uso de técnicas espectroscópicas de absorção de UV-Vis-NIR e fluorescência. Os resultados foram usados para estimar parâmetros de interação de cristal, estado de coordenação de íons Ni2+, parâmetros de Judd-Ofelt para íons Nd3+ e propriedades radiativas de íons metálicos em vidros. A difusividade térmica (D) e a condutividade térmica (K) dos NCs de ZnNiTe em vidros foram determinadas pelas técnicas de lente térmica (TL) e de relaxamento térmico (TR). Os resultados revelaram que os comportamentos de D e K nas amostras estudadas são semelhantes. As propriedades ópticas não lineares de NCs de ZnNiTe em vidros também foram estudadas usando a técnica de Z-scan. A propriedade de refração não linear foi observada apenas em amostras contendo 5% de Ni. Outras amostras, contendo de 1,0% a 10% de Ni apresentaram natureza de absorção não linear. Isto sugere que o coeficiente de absorção, não muda significativamente em função do comprimento de onda, mas sim devido ao aumento da concentração de Ni, efeitos de confinamento eletrônico e processos de absorção de dois fótons (TPA).PROQUALI (UFJF

Zn 1−x_{1-x} 1 - x Ni x_x x Te semiconductor nanocrystals in transparent glass for optoelectronic device applications

Abstract Doping glass with semiconductors, particularly with nanostructured semiconductors, has attracted attention due to the large optical absorption cross-sections of the latter. Based on this property, Ni $$^{2+}$$ 2 + (5 wt%) doped phosphate glass and Zn $$_{1-x}$$ 1 - x Ni $$_x$$ x Te (x = 0.5, 1.0, 5.0 and 10.0 wt% of Ni $$^{2+}$$ 2 + ) nanocrystals (NCs) doped phosphate glasses (GCs) were prepared by fusion method and subsequent heat treatment. Influence of Ni $$^{2+}$$ 2 + on structural, thermo-optical and third-order nonlinear optical properties have been analysed through various spectroscopic characterizations. The XRD pattern of the glass (G) exhibits the amorphous nature of the host material while GCs exhibit not only amorphous halo but also the presence of quantum dots (QDs) or nanocrystals (NCs) phases. TEM analysis of the studied GCs samples confirm the presence of quantum dots (QDs) and bulk NCs with an average diameter of approximately 4.2 $${\pm }$$ ± 0.3 nm and 13.4 $${\pm }$$ ± 0.2 nm, respectively. Several phosphate groups were observed and reported from Raman and FTIR-ATR spectra. The absorption band positions confirmed that Ni $$^{2+}$$ 2 + ions resemble to the octahedral symmetry. The intensity of absorption band around 1352 nm ( $$^3$$ 3 T $${_1}$$ 1 (F) $$\rightarrow$$ → $$^3$$ 3 A $${_2}$$ 2 (F)) increased with the increase of Ni $$^{2+}$$ 2 + in GCs which is an indicative of the $$^{[6]}$$ [ 6 ] Ni $$^{2+}$$ 2 + coordination. The emission properties such as emission cross-sections ( $${\sigma }_{emi}$$ σ emi ) full width at half maxima (FWHM) for the $$^1$$ 1 T $${_2}$$ 2 (D) $$\rightarrow$$ → $$^3$$ 3 T $${_2}$$ 2 (F) (visible) and $$^3$$ 3 A $${_2}$$ 2 (F) $$\rightarrow$$ → $$^3$$ 3 T $${_1}$$ 1 (F) (near-infrared) emission transitions were reported. Among the glass-containing semiconductor nanocrystals (GCs), the emission cross-sections in GC4 sample (x = 10% of Ni $$^{2+}$$ 2 + ) are the largest for both the visible (11.88 $$\times$$ × 10 $$^{-18}$$ - 18 cm $$^2$$ 2 ) and infrared (0.98 $$\times$$ × 10 $$^{-20}$$ - 20 cm $$^2$$ 2 ) transitions. Thermal diffusivity (D), thermal conductivity (K) and temperature dependent optical path length change (ds/dT) were obtained through time-resolved thermal lens (TL) and thermal relaxation (TR) methods. The D and K parameters do not change significantly with increase of Ni $$^{2+}$$ 2 + ions (0.5–5%) in GCs. Nonlinear-refractive index and nonlinear absorption of the studied samples were also obtained using femtosecond Z-scan technique. The increase of nonlinear absorption coefficient ( $$\beta$$ β ) is observed from GC2 (2.53 $${\times }$$ × 10 $$^{-10}$$ - 10 cm/W) to GC4 (7.98 $${\times }$$ × 10 $$^{-10}$$ - 10 cm/W). The GC4, sample with 10 wt% of Ni $$^{2+}$$ 2 + , showed the lowest ds/dT (1.22 $$\times$$ × 10 $$^{-6}$$ - 6 K $$^{-1}$$ - 1 ) with good lasing (FOM and emission cross-sections) and nonlinear absorption properties suggesting that it can be a good candidate for visible-red emission light conversion in LED technology