Doped Nano-luminescence Properties Of Ultrafine Particles

In this paper, the luminescent properties of doped semiconductor nanocrystals and rare earth doped nanocrystals have been studied. We studied that the effect of quantum confinement hi nanocrystals on energy levels and transition probabilities of impurity centers with the extension ranges of their wavefunctions differently, the effect of surface states and quantum size confinement in nanocrystals on energy transfer processes and the dominant mechanisms of the quenching have been discussed. The purpose of the paper is to study the luminescent processes of nanocrystals very deep and to provide the theoretical and experimental basis for establishing model of energy transfer and its practical application. The important result in the paper as following:Manganese doped zinc sulphide and copper doped zinc sulphide nanocrystals were prepared by coprecipitation method. Polymer films dispersed with ZnS:Mn and ZnS:Cu nanocrystals were prepared. Y2O3:Eu nanocrystals with different sizes and Y2O2S:Tb nanocrystals with different concentration have been prepared by combustion synthesis.It was studied that the effect of quantum confinement on SA luminescence center. The decay time of Mn has been accurate measured. The reason of lifetime shortening has been analyzed. It was also studied UV induced fluorescence enhancement in PVB film dispersed with ZnS:Mn nanoparticles.Based on the emission spectra and decay time, the effect of quantum confinement on energy levels and transition probabilities of Cu centers were discussed. The luminescent processes of G-Cu, B-Cu and R-Cu have been analyzed by the time-resolved spectra at room temperature and low temperature.The energy transfer between the Europium ions at different lattice sites hi cubic Y2O3 nanocrystals has been studied. The rate of energy transfer from Eu3+(C3i) to Eu3+(C2) in the case of Eu pairs is faster than for the isolated Eu(C3i) ions. The reason of quenching concentration increasing in Y2O3:Eu nanocrystals has been analyzed. We studied systematically the change of luminescence decay curve along with the change of size and concentration. The exchange interaction is considered to play the dominant role in the quenching of Eu emission. We fit the luminescence decay curve by the Inokuti-Hirayama theory. The efficiencies of energy transfer of exchange interaction have been calculated.We simulated two quenching mechanisms in nanocrystals by using monte-carlo method. They are surface states quenching center and bulk quenching center, the necessary conditions that doped nanocrystals become high efficiency luminescence material have been discussed.The energy transfer processes hi Y202S:Tb nanocrystals were studied. The quenchingconcentration of nanocrystals for quenching by cross relaxation is higher than that of bulk material. The dominant mechanisms of the quenching of 5D3 and 5D4 Tb34 emission were discussed. We fit the luminescence decay curve by the Inokuti-Hirayama theory. The energy transition efficiencies of 5D3 and 5D4 have been calculated. We fit the experimental curve by the theory formula of transition efficiencies and obtained the critical transfer concentration C0.Judd-Ofelt parameters of Y203:Eu nanocrystals were calculated by using J-O theory. The electric dipole and the nonzero magnetic dipole transition probabilities of 5D1-7FJ and 5D0-7F, in Eu3+ were calculated. We calculated the resonance energy transition probability of 5D0-7F2 of Eu3+ in Y2O3 nanocrystals. The Judd-Ofelt parameters were obtained from the emission spectra. Transition probabilities and integral intensity of 5D3-7FJ and 5D4-7FJ have calculated. The multipolar coupling transfer probabilities between the 5D3-5D4 and 7F6-7F0 were calculated on the basis of the theory of energy transfer. The relationship between emission intensities and concentration of Tb ion concentration have been obtained.