Study On Preparation And Optical Properties Of Tin Oxide Structure

Tin oxide (SnO2) was an important wide band gap metal oxide semiconductor material. Because of the excellent physical and chemical properties it was applied in many fields, such as gas sensors, transparent conductive films, solar cells, catalyst. Using the simple method, we prepared tin oxide quantum dots, core-shell structure microspheres and nanobelts and employed XRD, SEM and TEM to describe the structure and morphology of the samples. According to the results, the relationships between the morphology structures and growth conditions were given and the possible growth mechanism was also proposed. The properties of the sample were studied by the PL spectra and Raman spectroscopy. The findings and main conclusions were as follows:We fabricated SnO2quantum dots with the diameter size of about4～7nm by a hydrothermal method. High resolution transmission electron microscopy (HRTEM) shows that the quantum dot are in a good dispersion. The optical properties of the products were investigated by the room-temperature photoluminescence and the low-frequency Raman. PL showed that there was an intense emission peak centered at about600nm, of which was found in all samples with different sizes and could be attributed to the oxygen vacancy defects in the band gap. From the low-frequency Raman, a low frequency Raman peak at38cm-1was observed and shift to higher frequencies with decreasing the quantum dot size, which may be due to the phonon vibration of the sample surface. A special Raman peak was found at570cm-1. It was believed that this peak was the characteristic peak, with which the polycrystalline particle size reduce to a certain size.Using HMT as the active agent, we prepared SnO2core-shell structure microspheres with the spherical shell thickness of～200nm and the diameter of～2um by a hydrothermal method. The study of the impact of the concentration of HMT, NaOH, reaction time and temperature indicated that the active agent HMT play an important role in the formation of core-shell structure. No HMT, no core-shell structure. The surface of microsphere became smooth and the particles of microsphere decreased with the concentration of HMT increasing. The reason may be that the HMT prevent the growth of the SnO2nanoparticles. When the concentration of NaOH was too low, only the microsphere was formed. However, the hollow microsphere was formed with the concentration of NaOH increasing. An appropriate concentration brings the core-shell structure. The size of the particles increased with increasing the concentration of NaOH. With the extension of the reaction time, the product changed from the hollow ball to the core-shell structure microsphere, meanwhile the thickness of the spherical shell increasing. The microspheres and hollow spheres were at160℃, the core-shell structure at180℃. When the temperature rose to200℃, the core-shell structure changed to the hollow ball with a thick spherical shell. According to the above studies, the growth mechanism of the core-shell structure microspheres was proposed. It was observed that there was a peak at570cm-1in the Raman spectra again. The studies of the PL spectra showed that the wide602nm peak was due to the oxygen-related defects in the growth process.SnO2nanobelts were prepared via chemical vapor deposition method. The nanobelts were uniform,300-500nm in width,90nm in thickness and several tens of micrometers in length from the SEM and TEM. Ultraviolet-visible absorption spectra showed that the absorption edge of the nanobelts shift to high-energy. The band gap was larger than the value of3.62eV for bulk SnO2, which was probably due to the quantum size effect. PL spectra showed that there was a broad emission peak at602nm due to the oxygen vacancy defects, which brought in the growth process. Comparing to other samples, the peak of the sample prepared at1000℃showed a small red shift. The phenomenon may originate from the different band gaps due to the different morphologies and sizes. From the Raman spectra, the sample of1100℃had a weak Raman peak at695cm-1, which was not observed in bulk SnO2. The Raman mode may be the IR-active LO of modes, which was a consequence of disorder activation on the surface of the nanobelts.