Estudos de fenômenos óticos não lineares em nanocristais semicondutores para aplicações como marcadores biológicos

Abstract

In this work, we present the characterization of nonlinear optical phenomena in samples of CdTe/CdS core shell colloidal semiconductor nanocrystals synthesized in water using the mercaptosuccinic acid (MSA) or 3-mercaptopropionic acid (MPA) as stabilizers. Due to spatialconnement of electrons the nanocrystals exhibit quantum connement eects and are denominated quantum dots. These optical properties are important for application of the quantum dots as biological markers and for image acquisition by two photons excitation uorescence (TPEF). We implemented the experimental setups for photoluminescence and photoluminescence excitation (PLE) measurements using pulsed laser with femtoseconds pulses and the possibility to control the excitation laser repetition rate. We have also obtained images by two photons excitation uorescence (TPEF) and images by second harmonic generation (SHG) using a scanning optical microscope. The results applying the eective mass model show that the samples have a narrow size distribution. The emission spectrum by two photon absorption isnarrow (due the narrow size distribution) and the PLE spectrum shows a broad peak, allowing the use of a broad band of wavelengths of excitation. Depending on the power per pulse the nonlinear phenomena are more ecient and begins to saturate when the power is high. Finally,we present some preliminary tests of the application of quantum dots as biological markers in chicken embryos.