Synthesis, Photoacoustic And Photovoltage Characteristics Of ZnSe Quantum Dots

Zn Se quantum dots capped by ligand, L-Cysteine, were synthesized in aqueous solution. Samples were prepared depending on four different reaction conditions, heating temperature, value of pH, reflux time and ratio of ligand. Photoacoustic and photovoltaic properties of ZnSe QDs were analysed by PA and SPS.The crystal structure and size of ZnSe quantum dots were characterized by XRD. The analysis indicated that the structure of samples synthesized upon different reaction conditions was cubic zinc blende, and the ranges of size, 2.4-3.0nm of reflux temperature, 2.45-2.52 nm of pH, 2.48-2.53 nm of reflux time, 2.48-2.53 nm of ligand-ratio, respectively, were strong evidence for ensuring samples being quantum dots. Transmission electron microscopy(TEM), HRTEM and SAED were used to analyse microstructure and morphology of samples. The results showed that the particles were almost spherical shape, had good distribution uniformity and were polycrystalline structure. The main components and bond structure were characterized by FT-IR and Raman spectroscopy. And the core-shell structure, Zn Se/ZnS/ligand, was proven.In this thesis, PA and SPS were important measurements to analyze the photoexcited transition mechanism and the energy conversion behaviors. Analysis showed that the major way to releasing energy after illuminated by modulated light was nonradiative transition caused by lattice vibration during the incident wavelength of 300-400 nm and 700-800 nm, radiative transition for light emitting during 400-550 nm, nonradiative transition cooperated with radiative transition during 550-700 nm. All the results indicated that PA and SPS enjoyed the energy complementary relationship, and samples were all characterized by superior energy conversion efficiency. The analyzing upon EFISPS ensured samples exhibiting n-type semiconductor properties.Depending on different modulating frequency, 10-90 Hz, the analysis revealed that the relationship between PA response of sample prepared under 90 ℃ and modulating frequency of testing machine was well corresponded with R-G theory, the classical photoacoustic and photothermal theory. And the result also proved that the modulating frequency at 30 Hz was the optimum modulating frequency of testing machine.