In this work, we investigated the possible applications of Nd3+ ions doped lanthanium trifluoride (LaF3) nanocrystals as infrared constrast agents in the first and second biological windows of the electromagnetic spectrum, which extend from 700 to 1400 nm. For this, we use the three emissions of Nd3+ ions centered around 900, 1060, and 1330 nm, corresponding to transitions generated from the metastable state 4F3/2. In comparison with other fluorescent nanoparticles (NPs) used as biolables agents, such as semiconductor quantum dots and multiphotonic luminescent NPs, the Nd3+ doped LaF3 NPs present several advantages such as high fluorescence quantum efficiency and high chemical and spectral stabilities. We have demonstrated that, with the emission around 1060 nm is possible to obtain high brightness images of cancer cells and high penetration images of animal models (mices). Additionally, we have demonstrated that the emission around 900 nm has an appreciable thermal sensitivity that allows the use of such NPs as optical nanothermometers. As the Nd3+ concentration is increased to values around 25 mol%, this thermal sensitivity comes with a high conversion efficiency of light-to-heat, so that the NPs work as multifunctional agents capable of generating heat and measuring, simultaneously, induced local temperature. This has allowed the development of real time controlled thermal therapies of cancerous tumors in animal models (mices). / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta tese avaliamos as possíveis aplicações de nanocristais de trifluoreto de lantânio (LaF3) dopados com íons de Nd3+ como agentes de contrastes infravermelho na primeira e segunda janelas biológicas do espectro eletromagnético, as quais se estendem de 700 a 1400 nm. Para isso usamos as três emissões de íons de Nd3+ centradas em torno de 900, 1060 e 1330 nm, correspondentes a transições geradas a partir do estado metaestável 4F3/2. Na comparação com outras nanopartículas (NPs) fluorescentes usadas como agentes de bio-contrastes, tais como, pontos quânticos de semicondutores e NPs multifotônicas luminescentes, as NPs de LaF3 dopadas com íons de Nd3+ apresentam diversas vantagens, tais como, alta eficiência quântica de fluorescência e altas estabilidades química e espectral. Nós demonstramos com a emissão em torno de 1060 nm que é possível obter imagens de alto brilho de células cancerígenas e imagens de alta penetração de modelos animais (ratos). Adicionalmente, demonstramos que a emissão em torno de 900 nm apresenta uma apreciável sensibilidade térmica que permite utilizar tais NPs como nanotermômetros ópticos. Quando a concentração de íons de Nd3+ é elevada para valores em torno de 25 mol%, esta sensibilidade térmica vem acompanhada de uma alta eficiência de conversão luz-calor, fazendo as NPs se comportarem como agentes multifuncionais capazes de gerar calor e medir, de forma simultânea, a temperatura local induzida. Isto tem permitido o desenvolvimento de terapias térmicas, controladas em tempo real, de tumores cancerígenos em modelos animais (ratos).

Organic semiconductors are being investigated as an alternative to more traditional materials such as silicon, for the fabrication of different types of electronic devices. The advantages of such materials are flexibility, lightness and quick and low cost device production methods. In this thesis we analyze some small molecule organic semiconductors for their use in devices such as thin film transistors and photovoltaic cells. These materials, deposited in thin films on glass by thermal vacuum evaporation, are copper phthalocyanine (CuPc) and pentacene, p-type materials, fullerene (C60), PTCDA and PTCDI-C13, that are n-type. We analyze their optical properties by optical transmittance measurement and photothermal deflection spectroscopy (PDS). By such means we obtain the absorption coefficient of the materials in sub-gap region (near infrared - NIR), directly related with the density of electronic states. Furthermore, we examine thin film microstructure by X-ray diffraction (XRD) in order to observe if it is amorphous or polycrystalline. The data obtained by optical methods are used to calculate optical gap (Eg) and Urbach energy (Eu). The former of these parameters gives important information about the absorption properties of the material in the visible and NIR ranges of the spectrum, while the latter about the structural disorder in the film. Since a clear model for organic semiconductors is still not defined, in both cases we employ models that are usually considered in the case of inorganic semiconductors. The XRD analysis indicates that, in the deposition conditions used in this work, only C60 grows with amorphous structure while all the other materials are polycrystalline. Such result is used to determine which law can be used to estimate the optical gap: the general law for direct allowed electronic transitions in semiconductors for polycrystalline materials or the Tauc law for amorphous ones. The Urbach law, usually employed to have an idea about the amount of disorder in amorphous films, is used for all our materials as an indicator of thin film quality. Furthermore, we examine the stability of the materials over time under exposure to direct radiation and atmosphere and to compare the results with the ones obtained for samples simply exposed to atmosphere. PTCDA and CuPc have demonstrated to be stable against oxidizing agents that are present in atmosphere while the other materials suffer modifications in their optical properties. Such variations, principally located in the sub-gap region of the absorption region, indicate that an increase in the absorption level is obtained, probably due to the presence of defects that could work as charge carrier traps. Annealing treatments are performed on the degraded materials to observe that the degradation process is not reversible. Organic photovoltaic cells always include a heterojunction between two semiconductors, so the same study is performed on mixtures of two materials, a p-type and an n-type one, testing all the possible combinations between the investigated materials. The films are obtained by co-evaporating the two materials in 1:1 proportion. A mixture containing a degrading material also degrades. Heat treatments performed on the samples yield a partial crystallization of some materials but not of others and fail to recover the original optical properties when degradation occurs. Finally, two types of devices are fabricated: thin film transistors (TFTs) using PTCDI-C13 and diodes with CuPc. In the first case we obtain very interesting results, determining that the devices work as typical n-type channel transistors. An analysis of the device characterizations allows us to determine the density of electronic states in the channel obtaining a result that is very similar to the one obtained by optical means on the same material. In the second case we observe the typical diode behaviour but the response with light of such devices, characterized by having a structure similar to the one of Schottky type solar cells, is very low. / Los semiconductores orgánicos están siendo investigados como alternativos a materiales más tradicionales, como el silicio, para la fabricación de varios tipos de dispositivos electrónicos. Las ventajas que presentan tales materiales son flexibilidad, ligereza, rapidez y bajo coste de los métodos de producción de los dispositivos orgánicos. En esta tesis se analizan algunos semiconductores orgánicos de molécula pequeña para su aplicación en dispositivos como los transistores en capa delgada y las células fotovoltaicas. Tales materiales, depositados en capa delgada por evaporación térmica en vacío, son ftalocianina de cobre (CuPc) y pentaceno, de tipo p, fullereno (C60), PTCDA y PTCDI-C13, de tipo n. Se analizan las propiedades ópticas de ellos por medio de la medida de Trasmitancia Óptica y de la Espectroscopia de Deflección Fototérmica (PDS). Además se analiza la microestructura de las capas delgadas por difracción de rayos X (XRD) con el objetivo de observar si las capas tienen estructura amorfa o policristalina. Los datos son utilizados para calcular el gap óptico (Eg) y la energía de Urbach (Eu). Se analiza la estabilidad de los materiales con el pasar del tiempo y la exposición a irradiación directa, por un lado, y a la atmosfera, por otro lado. El fullereno es el único material que se deposita con estructura amorfa. Además se ha observado que CuPc y PTCDA son estables frente a la degradación por exposición a agentes oxidantes. Las células fotovoltaicas orgánicas incluyen siempre una heterounión entre dos semiconductores, así que se repite el mismo estudio sobre mezclas de dos materiales, uno de tipo p y otro de tipo n, probando todas las combinaciones posibles con los materiales analizados. Se observa que en una mezcla que incluya un material que presenta inestabilidad también hay degradación. Los tratamientos térmicos efectuados sobre las muestras han permiten obtener una parcial cristalización de algunos materiales pero no de otros y no llevan a recuperar las propiedades ópticas originarias, perdidas con la degradación. Finalmente, se fabrican dos tipos de dispositivos: TFTs de PTCDI-C13 y diodos de CuPc. En el primer caso se obtienen resultados interesantes, detectando que los dispositivos funcionan como típicos transistores en capa delgada de tipo n. En el segundo caso se observa el típico comportamiento de los diodos. Sin embargo, la respuesta con luz de tales dispositivos, de estructura análoga a fotocélulas de tipo Schottky, es muy escasa.