Nanoclusters de prata (Ag) e íons lantanídeos (Er3+, Pr3+, Yb3+) funcionalizados em materiais vítreos para geração de fonte de luz, camadas luminescentes para células solares de silício e aplicação em guias-de-ondas
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Data
2018-06-28
Autores
Silva, Tarcio de Castro
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Universidade Estadual Paulista (Unesp)
Resumo
Materiais vítreos se tornaram um dos mais atrativos materiais devido a fácil e rápida preparação. Durante as últimas décadas, várias aplicações têm sido exploradas e a viabilidade para mudança de frequência, conversão ascendente (upconversion) e descendente de energia (downconversion), geração de radiação visível com similaridade das emissões cromáticas azul, verde e vermelho; guia de onda, camadas luminescentes para células solares, geração de segundo harmônico e outros, estão publicadas. Propriedades estruturais como baixa energia de vibração estrutural (fônon), estabilidade química e ampla transparência óptica, tem sido o principal alvo para explorar uma excelente matriz para a dopagem com terras-raras. Por exemplo, íons Er3+ é um dos candidatos mais adequados para a propriedade de “upconversion” devido a absorção na região do infravermelho em 0,9 e 1,5 μm e consequente emissão na região do visível e infravermelho. Devido às suas propriedades espectroscópicas, os lantanídeos, geralmente, exibem emissões com linhas estreitas devido à fraca interação com o campo cristalino da matriz. Por outro lado, íons metálicos como a prata (Ag), exibem uma ampla banda de emissão e excitação. A propriedade mais interessante dos íons prata é que a emissão visível pode ser ajustada de acordo com a forma e tamanho das espécies de pratas presentes em uma amostra. Esta propriedade abre um largo espectro de aplicações nas quais a radiação visível pode ser explorada. Neste sentido, um dos principais objetivos dessa tese é mostrar a preparação de materiais vítreos contendo íons lantanídeos como Er3+ e Pr3+/Yb3+ e /ou íons prata e nanoclusters de prata para aplicação em camadas luminescentes para células solares, geração de luz branca, guia de onda e investigação dos processos de “upconversion” e “downconversion”. Para este propósito, materiais vítreos com composição molar 40InF3-20ZnF2-20Sr-20BaF2 (vidros fluoroindatos) e 50NaPO3-25ZnF2-15CdF2-10YF3 (vidros fluorofosfatos) foram selecionados. Os vidros fluoroindatos foram dopados com íons Er3+ com diferentes concentrações e os vidros fluorofosfatos com diferentes concentrações de pratas. Composições com diferentes concentrações de prata e os lantanídeos Pr3+/Yb3+ também foram preparadas. As amostras vítreas foram preparadas pelo método de fusão-choque térmico. Os materiais de partida foram pesados e homogeneizados em almofariz. A fusão dos compostos para os vidros fluoroindatos foram realizadas em tudo de platina a 850 °C durante 20 minutos e vertidos em um molde metálico pré-aquecido em 260 °C, enquanto que a obtenção dos vidros fluorofosfatos se deu com fusão a 1000 °C durante 30 minutos e vertidos em molde pré-aquecido a 300 °C. A primeira parte desta tese foi a preparação e avaliação das propriedades estruturais e espectroscópicas dos materiais vítreos. Absorção, excitação e espectros de emissão, o tamanho e morfologia dos nanoclusters de prata (para os vidros fluorofosfatos) bem como as propriedades térmicas foram analisadas. A segunda parte desta tese está relacionada com a aplicação dos vidros fluoroindatos como camadas luminescentes para o aumento da fotocorrente em uma célula solar de silício monocristalino e monofacial. Os vidros obtidos foram cortados e opticamente polidos de modo a obter amostras com as dimensões de 5.4 x 4.3 x 3.2 mm. As amostras foram colocadas na superfície de uma célula solar. Neste ponto, as diferentes concentrações de íons Er3+, que estão associadas à diferentes intensidades de emissão, foram analisadas nas medidas de fotocorrente. A terceira parte desta tese traz uma breve introdução aos nanoclusters de prata, que será a base para a compreensão dos resultados obtidos dos vidros fluorofosfatos. A maior parte dos resultados foram obtidos em colaboração com o “Institut de Chimie de la Matière Condensée de Bordeaux”, exceto os resultados das amostras preparadas para obtenção de radiação branca, capítulo 4. As amostras previamente preparadas com composição molar 45NaPO3-25MgF2-15CdF2-15YF3-5AgNO3, foram cortadas e polidas de modo a obter amostras com dimensão 7 x 4 x 2 mm. A estabilização dos nanoclusters de prata se deu através da técnica “Direct Laser Writing (DLW)”, utilizando laser de femtosegundo (fs) KGW:Yb, operando com linha espectral em 1030 nm e bombardeando a amostra com diferentes pulsos de energia. A irradiância laser foi controlada um modulador acústico-óptico permitindo a acumulação de N=105-106 com energia variando entre 20 e 150 nJ. As microestruturas de prata gravadas nas amostras foram avaliadas de acordo com suas propriedades de absorção e emissão. Em adição, neste amostra foi avaliada a viabilidade como guia de onda. Por último, na amostra com composição molar (30-x) NaPO3–30MgF2–30BaF2–10YF3–0.5Pr-0.5Yb - xAg (x = 0, 2, 4 and 10) foi analisada a transferência de energia dos nanoclusters de prata e os terras-raras Pr3+ e Yb3+. Os resultados apresentados nesta tese representam uma direção promissora para explorar materiais emissores com ampla emissão espectral com potencial uso em conversão descendente de energia “downconversion”, camadas para aplicações fotovoltaicas, fósforos e guias de ondas.
Glassy m aterials have becom e one of the m ost attractive m aterials owing their easy and fast preparation. During the last decades, several applications have been explored and the feasibility for frequency change, upconversion and downconversion, white light generation, waveguide, lum inescent layers for solar cell, second harm onic generation and other, are reported. Structural properties like low energy phonon, chem ical stability, broad transparence optical window have been the m ain target to explore a good h ost m aterials for lanthanides dopage. For exam ple, Er 3+ is one of the m ost suita ble candidate for upconversion since it has 1,5 μm and 0,9 μm absorption. Owing to their spectroscopic properties, lanthanides, generally, show visible em issions with narrow lines due to the poor interaction with the crystalline field of the host m aterial. On the other hand, m etal ions such as silver; generally, shows a broadban d em ission and absorption. The m ost interesting spectroscopic properties of silver is that the visible em ission m ay be tunable according to the size and shape of the silver species in the host m aterials. This property opens a large spectrum of application in which the visible light can be explored. In this sense, the m ain goal of this thesis is to show the preparation of glassy m aterials containing lanthanides such as Er 3+ , Pr 3+ /Yb 3+ and /or silver ions and nanoclusters for lum inescent layers for solar cell and photonic applications. The glassy m aterials selected for such purposes were fluoroindate glasses and fluorophosphate glasses. The sam ples were prepared by the conventional m elting - quenching m ethod. The raw m aterials with high purity were weighted and m ixed according to the following m olar com position: 40InF 3 - 20ZnF 2 - 20Sr - 20BaF 2 (fluoroindate glass) and 50NaPO 3 - 25ZnF 2 - 15CdF 2 - 10YF 3 (fluorophosphate glass). Besides, other com positions of fluorophosphate glasses were also synthesized. Fluoroindate glasses were doped with different Er 3+ am ount and the fluorophosphate glasses with different silver am ounts . The raw m aterials of the fluoroindate glasses were m elted in a platinum tube at 850 °C during 20 m inutes and poured out in a m old pre - heated at 260 °C. On the other hand, the raw m aterials of the fluorophosphate glasses were m elted in a platinum crucible at 1000 °C during 30 m in and poured out in a m ol pre - heated at 300 °C. The first part of this thesis was the preparation and the evalu ation of the structural and spectroscopic properties of these glasses. Absorption, excitation and em ission spectra , size and m orphology of the silver nanoclusters (for the fluorophosphate glasses) as well as therm al properties were analyzed. The second par t of this thesis is related to the application of the fluoroindate sam ples as lum inescent layers for enhance photocurrent in a m onocrystalline and m onofacial silicon solar cell. The glasses obtained were cut and polished in order to obtain sam ples with dim ensions 5.4 x 4.3 x 3.2 m m . The functional glass pieces were placed on the surface of the solar cell. At this point, the different Er 3+ am ount, which is associated with different upconversion intensity response s were eval uated in the photocurrent m easures. The third part of this thesis brings a brief introduction to the silver nanoclusters that will be the bases to understand the results obtained from the fluorophosphate glasses. Majority of these results was obtained in collaboration with “Institut de Chimie de la Matière Condensée de Bordeaux” , except the results of the sam ples for white light generation, shown in the chapter 4 . The sam ples previously prepared with m olar com position 45NaPO 3 - 25MgF 2 - 15CdF 2 - 15YF 3 - 5AgNO 3 , were cut and polished in order to obtai n sam ples with dim ension 7 x 4 x 2 m m . The stabilization of silver nanoclusters was carried out by direct laser writing (DLW technique), using a fem tosecond laser (KGW:Yb) operating at 1030 nm and delivering different energy pulses. The laser irradiance were controlled with an acousto - optic m odulator enabling the accum ulation of N=105 - 106 pulses with energy pulses going from 20 nJ up to 150 nJ . The m icrostructures of silver nanoclusters were evaluated according their a bsorption and em ission properties. Still, for this sam ple we also analyzed the feasibility as waveguiding m aterial. For last but no least, the sam ple with m olar com position ( 30 - x) NaPO 3 – 30 MgF 2 – 30BaF 2 – 10YF 3 – 0.5Pr - 0.5Yb - xAg (x = 0, 2, 4 and 10) was prepared in order to e valuate the energy transfer am ong the silver species and the rare earths Pr 3+ and Yb 3+ . The results presented in this thesis represent a promising direction to explore broadband emitter’s with potential use in down - conversion , layers for photovoltaic application, phosphors and waveguide . .
Glassy m aterials have becom e one of the m ost attractive m aterials owing their easy and fast preparation. During the last decades, several applications have been explored and the feasibility for frequency change, upconversion and downconversion, white light generation, waveguide, lum inescent layers for solar cell, second harm onic generation and other, are reported. Structural properties like low energy phonon, chem ical stability, broad transparence optical window have been the m ain target to explore a good h ost m aterials for lanthanides dopage. For exam ple, Er 3+ is one of the m ost suita ble candidate for upconversion since it has 1,5 μm and 0,9 μm absorption. Owing to their spectroscopic properties, lanthanides, generally, show visible em issions with narrow lines due to the poor interaction with the crystalline field of the host m aterial. On the other hand, m etal ions such as silver; generally, shows a broadban d em ission and absorption. The m ost interesting spectroscopic properties of silver is that the visible em ission m ay be tunable according to the size and shape of the silver species in the host m aterials. This property opens a large spectrum of application in which the visible light can be explored. In this sense, the m ain goal of this thesis is to show the preparation of glassy m aterials containing lanthanides such as Er 3+ , Pr 3+ /Yb 3+ and /or silver ions and nanoclusters for lum inescent layers for solar cell and photonic applications. The glassy m aterials selected for such purposes were fluoroindate glasses and fluorophosphate glasses. The sam ples were prepared by the conventional m elting - quenching m ethod. The raw m aterials with high purity were weighted and m ixed according to the following m olar com position: 40InF 3 - 20ZnF 2 - 20Sr - 20BaF 2 (fluoroindate glass) and 50NaPO 3 - 25ZnF 2 - 15CdF 2 - 10YF 3 (fluorophosphate glass). Besides, other com positions of fluorophosphate glasses were also synthesized. Fluoroindate glasses were doped with different Er 3+ am ount and the fluorophosphate glasses with different silver am ounts . The raw m aterials of the fluoroindate glasses were m elted in a platinum tube at 850 °C during 20 m inutes and poured out in a m old pre - heated at 260 °C. On the other hand, the raw m aterials of the fluorophosphate glasses were m elted in a platinum crucible at 1000 °C during 30 m in and poured out in a m ol pre - heated at 300 °C. The first part of this thesis was the preparation and the evalu ation of the structural and spectroscopic properties of these glasses. Absorption, excitation and em ission spectra , size and m orphology of the silver nanoclusters (for the fluorophosphate glasses) as well as therm al properties were analyzed. The second par t of this thesis is related to the application of the fluoroindate sam ples as lum inescent layers for enhance photocurrent in a m onocrystalline and m onofacial silicon solar cell. The glasses obtained were cut and polished in order to obtain sam ples with dim ensions 5.4 x 4.3 x 3.2 m m . The functional glass pieces were placed on the surface of the solar cell. At this point, the different Er 3+ am ount, which is associated with different upconversion intensity response s were eval uated in the photocurrent m easures. The third part of this thesis brings a brief introduction to the silver nanoclusters that will be the bases to understand the results obtained from the fluorophosphate glasses. Majority of these results was obtained in collaboration with “Institut de Chimie de la Matière Condensée de Bordeaux” , except the results of the sam ples for white light generation, shown in the chapter 4 . The sam ples previously prepared with m olar com position 45NaPO 3 - 25MgF 2 - 15CdF 2 - 15YF 3 - 5AgNO 3 , were cut and polished in order to obtai n sam ples with dim ension 7 x 4 x 2 m m . The stabilization of silver nanoclusters was carried out by direct laser writing (DLW technique), using a fem tosecond laser (KGW:Yb) operating at 1030 nm and delivering different energy pulses. The laser irradiance were controlled with an acousto - optic m odulator enabling the accum ulation of N=105 - 106 pulses with energy pulses going from 20 nJ up to 150 nJ . The m icrostructures of silver nanoclusters were evaluated according their a bsorption and em ission properties. Still, for this sam ple we also analyzed the feasibility as waveguiding m aterial. For last but no least, the sam ple with m olar com position ( 30 - x) NaPO 3 – 30 MgF 2 – 30BaF 2 – 10YF 3 – 0.5Pr - 0.5Yb - xAg (x = 0, 2, 4 and 10) was prepared in order to e valuate the energy transfer am ong the silver species and the rare earths Pr 3+ and Yb 3+ . The results presented in this thesis represent a promising direction to explore broadband emitter’s with potential use in down - conversion , layers for photovoltaic application, phosphors and waveguide . .
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Palavras-chave
Vidros fluoroindatos, Vidros fluorofosfatos, "Upconversion”, Downconversion, Transferência de energia, Célula solar, Nanoclusters de prata, Direct laser writing, Guias de onda