Chinese Journal of Luminescence
In the past, for the effects of doping content on the properties of materials and the optimum doping content problems, research workers only do experiments according to experiences, then give out some qualitative explanations, and there never quantitative calculation has been reported. In this paper, a theoretical model is investigated and the expression of optimum doping content is proposed. Starting from crystal structure, a theoretical expression of the relationship among the optimum doping content and the crystal structure coordination number and preparation methods has been set up.Assumption 1: If a doping atom replaces a lattice atom, and there is another doping atom in the near lattices, two such atoms meeting results in impurity bunching.Assumption 2: The atom energy change for different film preparation process can be divided as follows: For sol-gel method or reactive evaporation method, △E≈0. For magnetron sputtering method, △E≈(1/2)kT. For vacuum evaporation method, △E≈kT. For CVD method, △E≈(3/2)kT.The experimental data fits a parabola equation as:The optimum value of doping content isi=0,1/2,1,3/2,So according to the equality, we can calculate the optimum doping content in consideration of crystal structure and preparation methods.Using this expression, the optimum doping content of manganese-doped zinc sulfide nanocrystals can be calculated respectively. The typical values of quantitative calculation is: xopt≈5.88at%-7.69at%. Those values are just around 4at%-7at% and they are in accordance with the experimental results of Ref.  . The quantitative calculation results are in accordance with the experimental results. The author have been applied this method to calculate the optimum doping content of some other films successfully, such as some oxide semiconductor transparent conductive films, gas sensitive films, electrochromic films, ferroelectric films. The values are also in accordance with experimental results. Those results are reported in other papers latterly.The theoretical investigation in this paper may be shallow indeed and the results may be discreditable, but that calculation results are in accordance with experimental results may not be occasionally. The problem of optimum doping content must imply some rules undiscovered. We expect that this paper will be paid attention to, thus real theory of optimum doping content will rise as quickly as possible.