1. Full name:     Nguyen Duy Thien                                             2. Sex: male

3. Date of birth: 30/03/1986                                                        4. Place of birth: Bac Giang

5. Admission decision number: 4439/QĐ-ĐHKHTN

6. Changes in academic process: Extended time by decision No 4735/QD-DHKHTN dated on 28/12/2018 and 569/QD-DHKHTN dated on 14/02/2020, by Rector of  Rector of VNU University of Science.

7. Official thesis title: Study the effect of surface plasmon in metal nanoparticles (Au, Ag) on optical properties of some materials base on ZTO and SiO2 opal

8. Major: Solid State Physics                                        9. Code: 9440130.02

10. Supervisors:            The principal supervisor: Assoc.Prof. Dr. Le Van Vu

                                  The second supervisor:  Assoc.Prof. Dr. Nguyen Ngoc Long

11. Summary of the new findings of the thesis

- Zn2SnO4 nanocrystals (ZTO) and ZTO:Eu3+ have been successfully synthesized by a hydrothermal approach. The influence of technological conditions on the formation and development of ZTO nanocrystals was systematically investigated. In particular, on the base of the observation of morphology, the analysis of the XRD patterns and the selected area energy-dispersive X-ray spectroscopy, the thesis author analyzed the formation mechanism of the crystalline phases in the process of manufacture of ZTO nanocrystals in a strict and detailed. Optimum technological conditions for synthesis of the ZTO nanocrystals were as follows: the molar ratio of Zn/Sn was 2/1.25, pH concentration was 12.2, and the reaction temperature and duration were 200 oC and 4-6 h, respectively. The results of studying the photoluminescence showed that the ZTO samples exhibited two broad emission bands centered at 596 and 662 nm, related to lattice defects. The samples of ZTO:Eu3+ exhibited five emission peaks located at 579, 593, 615, 651 and 695 nm, related to optical centers Eu3+. The competition between luminescent centers Eu3+ and lattice defects in the samples of ZTO:Eu3+ was investigated.

- The effect of surface plasmon in Au nanoparticles on photoluminscent spectra of ZTO:Eu3+@Au nanocrystals was studied. The results showed that under 361 nm excitation, the intensity of the lattice defect emission was decreased, on the contrary, the intensity of the emission peaks of Eu3+ ion was increased with increasing of Au content in samples. Under excitation wavelength of 394 nm, the emission bands of the lattice defects did not appear; while the intensity of the emission peaks of Eu3+ ion was decreased with increasing of Au content. The reason of this phenomenon is the interaction between the plasmon of Au nanoparticles and the luminescent centers in the samples of ZTO:Eu3+. A diagram of energy transitions was proposed to adequately explain above mentioned phenomenon.

-  The SiO2 nanospheres with fairly uniformity have been successfully synthesized by Stober method. The effects of technological conditions on the formation and development of SiO2 nanospheres was systematically studied. From SiO2 spheres, the SiO2 opal periodic structure has been successfully fabricated by self-arranged method. The morphology and characteristic optical properties of SiO2 opal were studied in detail. The results showed that the peak position of the reflection spectra of the SiO2 opal changed with the size of the SiO2 spheres. The broad photoluminescence band of the SiO2 opal was a superposition of three spectral bands with the peaks at wavelengths 390, 440 and 480 nm.

-  The effect of plasmon on Ag nanoparticles on the luminescence spectra of SiO2 opal was studied in detail. The results showed that when the Ag nanoparticle content increased, the luminescent bands at the short wavelength side were extinguished faster than the bands on the long wave side. The reason is that the luminescence band at short wave side coincides with the top of the surface plasmon resonance absorption band of Ag nanoparticles.

     -  The Ag/SiO2 opal substrates were used to detect CBZ by the SERS technique. The SERS spectra of CBZ showed strong scattering peaks at 628, 726, 1006, 1227, 1274, 1462, and 1519 cm-1. The detection limit for CBZ was found to be 0.1 ppm using these substrates. This result opens up the prospect of using SERS spectroscopy to quickly determine CBZ residue on food and vegetables according to the standards of the Ministry of Health of Vietnam.

12. Pratical applicability, if any:

- ZTO@Au and ZTO: Eu3+@Au can be used to make dye-sensitized solar cell, photocatalytic materials etc.

- The Ag/SiO2 substrates can be used to quickly determine CBZ residue on food and vegetables according to the standards of the Ministry of Health of Vietnam.

13. Further research directions, if any

-  Study the effect of surface plasmon in Au, Ag nanoparticles on optical properties of Si nanowires and applications.

14. Thesis-related publications:

[1] Nguyen Duy Thien, Ngo Nhu Viet, Nguyen Ngoc Long, Le Van Vu (2015), “Synthesis and optical properties of Zn2SnO4:Eu3+ nanocrystals”, VNU Journal of Science: Mathematics-Physics, 31(1S), pp.66-72.

[2] Nguyen Duy Thien, Nguyen Ngọc Tú, Ngo Như Viet, Nguyen Duy Phuong, Le Van Vu, Nguyen Ngoc Long (2015), “Hydrothermal Synthesis and optical properties of undoped and  Eu3+-doped zinc stanate nanocrystals”, Communications in Physics, 25(4), pp.327-339.

[3] Nguyễn Duy Thiện, Nguyễn Ngọc Long, Lê Văn Vũ (2017), “Ảnh hưởng của hạt nano vàng lên tính chất huỳnh quang của vật liệu Zn2SnO4: Eu3+”, Kỷ yếu Hội nghị Vật lý chất rắn và Khoa học vật liệu toàn quốc lần thứ 10, 208 -211.

[4] Nguyen Duy Thien, Le Van Vu, Nguyen Ngoc Long (2018), “The effect of interaction between surface plasmons of gold nanoparticles and optical active centers on luminescence of Eu3+-doped Zn2SnO4 nanocrystals”, Optical Materials, 78, pp.319-324.

[5] Nguyen Duy Thien, Nguyen Ngoc Tu, Nguyen Quang Hoa, Sai Cong Doanh, Nguyen Ngoc Long, Le Van Vu (2019), ”Detection of Carbendazim by SERS Technique Using Silver Nanoparticles Decorated SiO2 Opal Crystal Substrates”, Journal of Electronic Materials, 48, pp.8149-8155.

[6] Nguyen Duy Thien, Luu Manh Quynh, Le Van Vu and Nguyen Ngoc Long (2019), “Phase transformation and photoluminescence of undoped and Eu3+-doped zinc stannate (Zn2SnO4) nanocrystals synthesized by hydrothermal method”, Journal of Materials Science: Materials in Electronics, 30, pp.1813-1820.

[7] Nguyen Duy Thien, Nguyen Ngoc Tu, Nguyen Quang Hoa, Sai Cong Doanh and Le Van Vu (2021), “Fabrication, characterization of SiO2 nanospheres and SiO2 opal photonic crystals”, VNU Journal of Science: Mathematics-Physics, 37(1). pp. 68-73.