Excitation Of Si_xO_y (x,y=1,2,3) Molecule Under External Electric Fields

In recent years, luminescence from silicon-based materials under the action of external electric field or light field has been an important research subject. Exploring silicon-based luminescent materials is necessary and it is the key of investigation to photoelectron integration lamp-house. At present, spectrums from ultraviolet to infrared have been observed extensively experimentally, but it is hysteretic in theory. It is proved that silicon-rich SiO₂ materials are important silicon-based materials luminescence materials, however, its microstructure is still uncertain and the theory of luminescence is also a subject of controversy. It is known that the properties of materials account for the properties of the molecules and the excited states under external electric field are critical to the study on luminescence. At present, the ground state properties of molecules have been researched extensively in theory but the study on excited states of molecules is lacking. Therefore, the study on excited states of molecules under external electric or light field from the level of atom and molecule is very important and significative.In this paper, the microstructures of some main silicon-rich SiO₂ molecules have been studied and the excited states also been analyzed. All the calculations are executed using Gaussian 03 program package. Density function theory (DFT) is an effectual and convenient method to research the ground structure and the excited properties. Therefore, at first the geometry of Si_xO_y molecule (Si₂O, Si₃O, Si₂O₂, Si₃O₂, Si₃O₃) is optimized using DFT ( B3p86 or B3lyp ) method. Then, on the basis of optimum structure, the excited properties of Si_xO_y molecule are calculated using CIS-DFT or TD-DFT method under no external electric field as well as external electric field. The oscillator strength, transition electric dipole momentμ, excited energy E and absorption spectrum also been calculated. On this basis, the possibility of luminescence from Si_xO_y molecule been analyzed and this improves the luminescence properties of silicon-rich SiO₂ molecules in the theory.Oxygen-deficient defects theory is a main theory to explain the luminescence from silicon-based materials. In the manufacturing process of silicon-rich SiO₂ materials, there must be many oxygen-deficient defects for the relative decrease of oxygen. Our results correspond with the experiment values perfectly which suggests the structure of Si_xO_y molecule is excepted to be one of the main basic microstructures of the materials so, the oxygen -deficient defect structural model for Si_xO_y molecule also has been provided to research the microstructures of the materials.