Of Zns Nano-crystalline Structure, Defects And Luminescence

In this thesis, we studied systematically the influence of the annealing on the crystallite structure and fluorescence of ZnS nanoparticles and the surface state of ZnS nanoparticles. The main results and innovation are as follows:1. ZnS nanocrystallite was prepared by co-precipitation. The size variation of annealed nanoparticles was studied with the treatment temperature. The result shows that, for the size of 11nm ZnS nanoparticles, they grow up dramatically when the treatment temperature exceeding 600℃, and have been 3-5 um when the treatment temperature increasing to 900℃. The grown-up of nanoparticles during thermal treatment is also explained from the aspect of energy.2. The critical temperature from cubic to hexagonal phase was measured for the 11 -nm ZnS nanoparticles. The result shows that the transition temperature is 618℃, which, is far bellow than that in bulk materials (1020℃), which is attributed to the bigger surface tension of nanoparticles.3. The luminescence intensity of annealed nanoparticles was compared with that of the commercial bulk powders. The result shows that the emission of the former is far weaker than that of the latter. In addition, a emission band centered at 520nm was observed in all the annealed nanoparticles while it did not appear all the time in the commercial bulk powders. Considering the 520nm emission originates from donor-acceptor recombination, we suppose that in nanoparticles it may be easier to form defect levels acting as acceptor state. The doping of europium did not induce any new luminescent centers, but caused the luminescent efficiency of defects to increase greatly.4. By changing the rinse times during the synthesis of ZnS nanocrystallite, the surface state was studied. The result shows that with increasing rinse times, the emission intensity decreases dramatically. It concluded that self-activated luminescent centers are not distributed randomly but prefer to occupy the surface sites innanoparticles.5. By Raman spectra, EPR spectra and UV irradiation-induced spectra change, the organic function groups of -OH, -CH3 and -COO adsorbed electrically on the surface of nanoparticles were discussed. On one hand, these organic function groups decorate the surface of nanoparticles by combining with the surface dangling bonds. And most important, they may act partially as the donor of D-A pairs in the SA luminescence by providing electrons.