Enhanced Luminescence Efficiency Of Rare-earth Doped Si-based Thin Films By Energy Resonant Transfer Process

With the announcement of the22-nanometer chip manufacturing process from the Intel Corporation, the feature size of devices is gradually reduced and the development of silicon microelectronic industry has nearly come to the physics limits. One of the possible solutions is realize Si-based optoeletronic integrated circuits by combining the micro-eletronic devices with photonic devices on one chip. So far, the most challenging work is to find an efficient and stable silicon-based light source. On the other hand, the development of the cheap and high efficiency solar cells cause great interest from researchers all around the world. In order to improve the efficiency of solar cells and break through the Shockley-Queisser theoretical limit, it is necessary to find a suitable approach, such as up-conversion and down-conversion to make full use of the solar spectrum.As one of important silicon-based thin film functional materials, the trivalent rare-earth (RE) ions and nano-crystals co-doped silica thin film has caused great interest. Owing to the abundant energy levels arising from the4f inner shell configuration of RE ions and the quantum confinement effect of the nano-crystals, the RE ions and nano-crystals co-doped silica thin film is of great significance on the silicon-based optoelectronic integration and high efficiency solar cells.In this thesis, the RE ions and nano-crystals co-doped silica thin films were prepared by sol-gel and spin coating methods. The influence of doping concentrations and the post annealing temperatures to the average size of the nano-crystals doped in the silica thin film were systematically evaluated. On this basis, the SnO2nano-crystals and Eu3+(Er3+) co-doped silica thin film were prepared. The influences of doping and annealing conditions on the photoluminescence from Eu3+(Er3+) were discussed. The main content of the thesis is listed as follows:1. The metal-oxide nano-crystals doped silica thin films were prepared by sol-gel and spin coating methods. The formation of tetragonal rutile phase’s SnO2nano-crystals and hexagonal phase’s ZnO nano-crystals with uniform distribution was confirmed by the X-ray diffraction and the transmission electron microscopy. By controlling the doping concentrations and the post annealing conditions, we can control the particle size of the nano-crystals. Room temperature PL and PLE spectra of nano-crystals doped silica thin film were evaluated. The wide PL was originated from the defect states such as oxygen vacancies on the nano-crystals surface and the sharp PLE peak was slightly red-shifted as the increasing doping concentrations due to the enlargement of the average particle size.2. We fabricated the SnO2nano-crystals and rare-earth Eu3+ions co-doped SiO2thin films. It was found that the intensity of the emission from5D0-7F2transitions of the Eu3+ions was enhanced by150times due to the energy transfer from the oxygen-vacancy-related defects of SnO2nano-crystals to nearby Eu3+ions. The influences of Sn amounts and the post annealing temperatures were systematically evaluated to further understand the mechanism of the energy transfer. The luminescence intensity ratio of Eu3+ions from the electric dipole transition and the one from the magnetic dipole transition indicated the different probable locations of Eu3+ions in the sol-gel thin films which were further discussed based on temperature-dependent photoluminescence measurements.3. Er3+ions embedded in silica thin films co-doped by SnO2nano-crystals were fabricated by sol-gel and spin coating methods. A strong characteristic emission located at1540nm from Er3+ions can be identified and the PL intensity increases monotonously with the increasing Sn concentrations from0to20mol%, which can be attributed to more SnO2nano-crystals involved in energy transfer process. However, superfluous Sn will lead to luminescent saturation and quench when the concentration of Sn is more than20mol%, which may be explained that excessive concentrations lead to the agglomeration of nano-crystals and decrease in surface-to-volume ratio due to the increased particle size and influence the efficiency of the energy transfer. The emission at1540nm from Er3+ions can be enhanced by more than three orders of magnitude, which can be attributed to the effective energy transfer from the defect states of SnO2nano-crystals to nearby Er3+ions as revealed by the selective excitation experiments. It is an effective way to enhance luminescence by co-doping appropriate Sn concentrations.