1. Full name: Hoang Manh Ha                                        2. Sex: Male

3. Date of birth: 08/10/1982                                            4. Place of birth: Vinh Phuc

5. Admission decision number: No 4374/QĐ-KHTN-CTSV dated on 03/12/2012, by Rector of VNU University of Science.

6. Changes in academic process:          

- Extension Decision No 741/QD-DHKHTN dated on 31/3/2016 and 1034/QD-DHKHTN dated on 25/4/2017 by Rector of VNU University of Science

- Decision No 5000/QD-DHKHTN dated on 29/12/2017 by Rector of VNU University of Science that sending PhD. student back to office.

7. Official thesis title: “Synthesis and study optical properties of rare earth doped Nanofluorit LaF3:RE3+ (RE3+: Sm3+, Ho3+, Eu3+)”

8. Major: Solid state Physics                 9. Code: 62 44 01 04

10. Supervisors:            PGS. TS. Le Van Vu

                                    PGS.TS. Nguyen Ngoc Long    

11. Summary of the new findings of the thesis

- The LaF3 and LaF3:Sm3+ nanocrystals have been synthesized hydrothermal method. The nanocrystals possess hexagonal structure with  space group. The lattice parameters were calculated to be a = 7.167 Ǻ and c = 7.323 Ǻ. Absorption, PL and PLE spectra related to Sm3+ ion have been investigated in detail. Judd–Ofelt theory has been applied to the absorption spectrum to estimate Wl (λ = 2, 4, 6) intensity parameters. The results show that W2 = 6,176x10-20 cm2, W4 = 7,997x10-20 cm2 and W6 = 3,098x10-20 cm2 with the r.m.s deviation of oscillator strength s = 0,273x10-6. Based on the obtained JO intensity parameters, the radiative properties of the 5G5/2 excited level have been predicted. It is found that 4G5/2 à 6H7/2 (594 nm) transition has the highest radiative transition rate compared to the other transitions. In addition, the 4G5/2 à 6H7/2 transition has maximal experimental branching ratio (bexp = 55,5%) and maximal stimulated emission cross-section (sem(lp) = 10,8x10-22 cm2). Luminescence quantum efficiency of the excited 4G5/2 state of Sm3+ ion in LaF3 nanocrystals is determined to be 82 %. 

- The photocatalytic activity of the prepared LaF3:Sm3+ nanocrystals was demonstrated by decomposing R6G under UV light radiation. The photodegradation rate constant k increases from 0.012 to 0.032 min‒1 with the decrease of LaF3:Sm3+ nanocrystal size,which makes it a promising candidate in the application of environmental pollutant treatment.

- Ho3+-doped LaF3 nanocrystals with 1.0, 3.0, and 5.0 mol% Ho3+ have been prepared by hydrothermal method. The nanocrystals possess hexagonal structure with  pace group with lattice parameters a = 7.172 Å and c = 7.342 Å. The room temperature absorption, luminescence spectra of LaF3:Ho3+ was investigated in detail. Judd-Ofelt theory has been applied to estimate Wl (λ = 2, 4, 6) intensity parameters. For LaF3:5%Ho3+ sample, W2 = 1,872x10-20 cm2, W4 = 4,006x10-20 cm2 and W6 = 4,720x10-20 cm2. Based on these JO parameters, various radiative parameters such as radiative transition probabilitiesn , radiative lifetime  , branching ratios  and stimulated emission cross-section  for various emission levels of LaF3:5%Ho3+ sample have been determined. It is found that the luminescence quantum efficiency of 5F5 excited state is decreased from 55,8 to 37,9 % with increasing Ho3+ concentration from 1 to 5 mol%.

- LaF3:Eu3+ nanocrystals were prepared by hydrothermal method. The optical properties of Eu3+-doped LaF3 nanocrystals have been investigated. The small value of R and Ω2 parameter shows that the coordination structure surrounding the Eu3+ ions has high symmetry and Eu3+ - F- bond has low polarizability. The radiative parameters show that the 5D5/2→7F1 transition of Eu3+ ions in LaF3 nanocrystals is very useful fiber optic amplifier.

12. Practical applicability, if any:

13. Further research directions:

- Synthesis and study optical properties of rare earth doped Nanofluorit.

14. Thesis-related publications:

[1] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2018), “Radiative transition dynamics of holmium ions-doped LaF3 Nanocrystals”, Journal of Materials Science: Materials in Electronics, 29, pp. 1607–1613.

[2] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2017), “Optical properties and Judd–Ofelt analysis of Sm ions in Lanthanum trifluoride nanocrystals”, Journal of Materials Science: Materials in Electronics, 28, pp. 884–891.

[3] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2016), “Photoluminescence and Energy Transfer Between Sm3+ Ions in LaF3 Nanocrystals Prepared by Hydrothermal Method”, International Journal of Materials Science and Applications, 5(6), pp. 284-289.

[4] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2017), “Photocatalytic properties of LaF3:Sm3+ nanocrystals prepared via hydrothermal technique”, JOURNAL OF SCIENCE OF HNUE: Material Sci. Vol. 61, No. 9A, pp. 75-82.

[5] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2016), “Synthesis and Optical Properties of Ho3+, Pr3+ Co-doped LaF3 Nanocrystals”, VNU Journal of Science: Mathematics – Physics, Vol. 32, No. 4, pp. 26-31.

[6] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, Phan Van Do, (2016), “OPTICAL PROPERTIES OF EU3+ IONS IN LAF3 NANOCRYSTALS”, Journal of Science and Technology, Vol 54, No. 1A, pp. 88-95.

[7] Hoang Manh Ha, Tran Thi Quynh Hoa, Le Van Vu, Nguyen Ngoc Long, (2015), “Optical properties of LaF3: Ho3+ nanoparticles prepared by hydrothermal method”, VNU Journal of Science: Mathematics – Physics, Vol. 31, No. 1S, pp. 11-16.

[8] Hoàng Mạnh Hà, Trần Thị Quỳnh Hoa, Lê Văn Vũ, Nguyễn Ngọc Long, (2013), “TÍNH CHẤT CẤU TRÚC VÀ TÍNH CHẤT QUANG CỦA CÁC HẠT NANO LaF3:Sm3+ CHẾ TẠO BẰNG PHƯƠNG PHÁP THỦY NHIỆT”, Tuyển tập báo cáo Hội nghị Vật lý chất rắn và Khoa học vật liệu toàn quốc lần thứ 8, Thái Nguyên, trang 166-170.