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Information on Doctoral thesis of Fellows Tran Thi Quynh Hoa

Official thesis title: Fabrication and characterization of ZnS nanomaterials
1. Full name: TRAN THI QUYNH HOA               
2. Sex: Female
3. Date of birth: 22/03/1982                                           
4. Place of birth: Hanoi, Vietnam
5. Admission decision number: 2385/SĐH dated 29 Jun 2007 by President of Vietnam National University, Hanoi
6. Changes in academic process: None
7. Official thesis title: Fabrication and characterization of ZnS nanomaterials
8. Major: Solid State Physics                                       
9. Code: 62 44 07 01
10. Supervisors: Assoc. Prof. Dr. Nguyen Ngoc Long; Assoc. Prof. Dr. Ta Dinh Canh
11. Summary of the new findings of the thesis
· First time in Vietnam, the ZnS nanocrystals with the size of several nanometers have been successfully fabricated by using a sonoelectrochemical method. The ZnS nanocrystals possess a face-centered-cubic structure and exhibit the quantum confinement effect. In these nanocrystals the surface defects play an important role in optical processes.
· The ZnS host nanocrystals and the Mn-doped ZnS nanocrystals have been successfully synthesized by hydrothermal method. The mechanism of photoluminescence and photoluminescence excitation in these nanocrystals has been analyzed in detail. In particular, the optical transitions within 3d levels of Mn2+ ion were observed at the same time in the diffuse reflection, absorption, photoluminescence and photoluminescence excitationspectra in the range of temperature from 10 K to room temperature. The photocatalytic properties of the ZnS and ZnS:Mn samples have been studied to decolorize waste in the textile dyeing industry.
· The surface passivation of ZnS:Mn nanoparticles by the TG organic and ZnS inorganic shells has been successfully performed. It was found that the coating ZnS:Mn nanocrystals with a shell remarkably decreased the surface defects, therefore, enhanced the emission of Mn2+ ions. In addition, the overcoating ZnS:Mn nanocrystals decreased the strength of quantum confinement, therefore, made the band edge of core/shell nanocrystals shift to the lower energy side compared with the bare nanocrystals

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