NGHIÊN CỨU TÍNH CHẤT HẤP THỤ VÀ QUANG HUỲNH QUANG CỦA NANO TINH THỂ CdxZn1-xS PHA TẠP Cu LUẬN VĂN THẠC SĨ VẬT LÝ

BỘ GIÁO DỤC VÀ ĐÀO TẠO VIỆN HÀN LÂM KHOA HỌC VÀ CÔNG NGHỆ VIỆT NAM HỌC VIỆN KHOA HỌC VÀ CÔNG NGHỆ - Trần Ánh Quang NGHIÊN CỨU TÍNH CHẤT HẤP THỤ VÀ QUANG HUỲNH QUANG CỦA NANO TINH THỂ CdxZn1-xS PHA TẠP Cu LUẬN VĂN THẠC SĨ VẬT LÝ Hà Nội - 2019 BỘ GIÁO DỤC VÀ ĐÀO TẠO VIỆN HÀN LÂM KHOA HỌC VÀ CÔNG NGHỆ VIỆT NAM HỌC VIỆN KHOA HỌC VÀ CÔNG NGHỆ - Trần Ánh Quang NGHIÊN CỨU TÍNH CHẤT HẤP THỤ VÀ QUANG HUỲNH QUANG CỦA NANO TINH THỂ CdxZn1-xS PHA TẠP Cu Chuyên ngành: Vật lý chất rắn Mã số: 44 01 04 LUẬN VĂN THẠC SĨ VẬT LÝ NGƯỜI HƯỚNG DẪN KHOA HỌC: Hướng dẫn 1: TS Nguyễn Thị Thúy Liễu Hướng dẫn 2: PGS.TS Nguyễn Xuân Nghĩa Hà Nội - 2019 Lời cam đoan Tôi xin cam đoan công trình nghiên cứu tơi hướng dẫn TS Nguyễn Thị Thúy Liễu PGS.TS Nguyễn Xuân Nghĩa Các kết nghiên cứu trình bày luận văn trung thực, khách quan thông tin trích dẫn rõ nguồn gốc Quảng Bình, ngày 09 tháng 10 năm 2019 Học viên Trần Ánh Quang Lời cảm ơn Lời đầu tiên, xin bày tỏ lòng biết ơn sâu sắc tới TS Nguyễn Thị Thúy Liễu - người tận tình hướng dẫn, động viên giúp đỡ tơi suốt q trình thực luận văn Tôi xin cảm ơn PGS TS Nguyễn Xn Nghĩa tận tình dẫn, góp ý cụ thể cho nghiên cứu khoa học Tôi xin trân trọng cảm ơn giúp đỡ, tạo điều kiện thuận lợi Học viện Khoa học Công nghệ - Viện Hàn lâm Khoa học Công nghệ Việt Nam q trình tơi thực hồn thành luận văn Xin cảm ơn hỗ trợ, động viên từ gia đình bè bạn tạo động lực to lớn giúp tơi hồn thành luận văn Nghiên cứu tài trợ Quỹ Phát triển khoa học công nghệ Quốc gia (NAFOSTED) đề tài mã số 103.02-2017.54 Trần Ánh Quang Danh mục ký hiệu chữ viết tắt Các ký hiệu x d r aZb aWz, cWz α γ C β θ  ν h Eg Eu Ec e Hàm lượng thành phần hóa học nano tinh thể Đường kính nano tinh thể Bán kính nano tinh thể Hằng số mạng tinh thể cấu trúc zinc blende Các số mạng tinh thể cấu trúc wurtzite Độ hấp thụ Hệ số dập tắt Nồng độ nano tinh thể mẫu dung dịch Độ rộng đỉnh nhiễu xạ nửa cực đại Góc nhiễu xạ Bước sóng me* Tần số Hằng số Planck Năng lượng vùng cấm Năng lượng Urbach Năng lượng trạng thái điện tử Điện tích điện tử Khối lượng hiệu dụng điện tử mh* Khối lượng hiệu dụng lỗ trống mr  Khối lượng rút gọn điện tử lỗ trống Bậc phản xạ Nồng độ điện tử Hằng số điện môi vật liệu o Hằng số điện môi chân không ’ Ứng suất n n’ b ΔEMB ΔAH ΔPH Hằng số bowing quang học Độ dịch lượng Moss-Burstein Độ dịch đỉnh hấp thụ thứ Độ dịch đỉnh phát xạ lượng cao Các chữ viết tắt NC Nano tinh thể Zb Zinc blende Wz Wurtzite XRD Nhiễu xạ tia X EDX Tán sắc lượng tia X AAS Phổ hấp thụ nguyên tử PL Quang huỳnh quang EH(A) Vị trí đỉnh phát xạ lượng cao NC Cd0,5Zn0,5S EH(B) Vị trí đỉnh phát xạ lượng cao NC Cd0,5Zn0,5S:Cu Danh mục bảng Bảng 3.1 Trang So sánh hàm lượng x tính tốn kết phân tích 36 EDX AAS Danh mục hình vẽ, đồ thị Hình 1.1 Hình 1.2 Hình 1.3 Hình 1.4 Hình 1.5 Hình 1.6 Trang Sự phụ thuộc hàm lượng tạp Mn NC ZnxCd1-xS vào thành phần x (a) Phổ hấp thụ, (b) phổ PL, (c) màu phát xạ NC ZnxCd1-xS:Cu/ZnS chế tạo với tỷ lệ Zn/Cd khác Mơ tả q trình pha tạp Cu vào NC ZnxCd1-xSe 10 Đồ thị biểu diễn lượng vùng cấm NC Zn xCd1- 11 xSe phụ thuộc vào kích thước hàm lượng thành phần Đường liền nét kết tính tốn lý thuyết; ký hiệu ●, ○, Δ, × thể kết thực nghiệm Khoảng phổ phát xạ NC bán dẫn pha tạp khác 13 Khoảng bước sóng phát xạ InP:Cu mở rộng đến 1100 nm số liệu giới hạn vùng nhìn thấy Giản đồ lượng minh họa (a) q trình kích thích 14 (b) q trình rã kích thích 1 lượng trạng thái bản, 2 biểu diễn lượng trạng Hình 1.7 thái kích thích Giản đồ lượng (a) q trình kích thích (b) q trình rã kích thích NC bán dẫn pha Mn 1, 2, 3 mô tả trạng thái (mạng + Mn), (mạng nền* + Mn), (mạng + Mn*) với ký hiệu * trạng thái kích thích 14 Hình 1.8 Hình 1.9 Hình 1.10 Hình 1.11 Hình 1.12 Hình 2.1 Hình 3.1 Hình 3.2 Hình 3.3 Hình 3.4 Hình 3.5 Hình 3.6 Giản đồ lượng NC ZnS pha tạp Mn có trạng thái bề mặt/sai hỏng Các q trình kích thích rã kích thích (a) NC khơng pha tạp (b) NC pha tạp Các đoán nhận khác vị trí mức lượng ion Cu2+ vật liệu bán dẫn II-VI Vị trí mức lượng ion Cu vật liệu InP, ZnSe, CdS ZnS Các vị trí xác định vị trí lượng phát xạ thấp ion Cu Sơ đồ giải thích hình thành chân hấp thụ Urbach Giản đồ cấu trúc vùng lượng với trạng thái điện tử lấp đầy hoàn toàn hàm phân bố điện tử với mức Fermi vùng dẫn Minh họa hình học định luật nhiễu xạ Bragg Ảnh TEM giản đồ phân bố kích thước mẫu NC nền: (a) Cd0,3Zn0,7S; (b) Cd0,5Zn0,5S; (c) Cd0,7Zn0,3S; mẫu NC pha tạp % Cu: (d) Cd0,3Zn0,7S:Cu; (e) Cd0,5Zn0,5S:Cu; (f) Cd0,7Zn0,3S:Cu Ảnh TEM giản đồ phân bố kích thước mẫu NC Cd0,4Zn0,6S:Cu có hàm lượng Cu: (a) %; (b) 0,2 %; (c) % Kích thước trung bình mẫu NC Zn1-xCdxS NC Zn1-xCdxS:1 % Cu có hàm lượng x = 0,3; 0,4; 0,5; 0,7 Phổ EDX mẫu NC Cd0,7Zn0,3S Phân tích Rietveld mẫu: (a) NC Cd0,4Zn0,6S NC Cd0,4Zn0,6S:1 % Cu; (b) NC Cd0,7Zn0,3S NC Cd0,7Zn0,3S:1 % Cu Các giản đồ XRD pha Zb Wz tương ứng phân biệt màu nhạt màu đậm (a) Sự thay đổi số mạng tinh thể pha cấu trúc Zb Wz (b) tỉ phần pha cấu trúc Wz theo hàm lượng thành phần x mẫu NC CdxZn1-xS NC CdxZn1-xS:1 % Cu Các số mạng tinh thể NC 15 19 20 21 22 30 34 35 36 36 37 38 Hình 3.7 Hình 3.8 Hình 3.9 Hình 3.10 Hình 3.11 CdxZn1-xS NC CdxZn1-xS:1 % Cu tương ứng nhóm ký hiệu (○, □, ∆) (●, ■,▲) (a) Phân tích Rietveld giản đồ XRD mẫu Cd0,4Zn0,6S:Cu với hàm lượng Cu khác khoảng % - 1,5 %; (b) Sự thay đổi tỉ phần pha Wz theo hàm lượng tạp Cu Đường liền nét thể xu hướng thay đổi tỉ phần pha Wz Ảnh TEM (a) mẫu A (b) mẫu B (a) Minh họa phân tích Rietveld giản đồ XRD, (b) chứng hợp kim đồng mẫu A (a) Các phổ hấp thụ, PL, (b) phổ PL phụ thuộc cơng suất kích thích mẫu A B Sự thay đổi (a) lượng phát xạ (b) tỉ số cường 39 40 40 41 42 độ tích phân IL100/(IL+IH) mẫu A B Hình 3.12 Hình 3.13 Hình 3.14 Hình 3.15 mối liên quan với cơng suất kích thích quang (a) Phổ hấp thụ (b) phổ PL mẫu NC Cd0.4Zn0.6S không pha tạp pha tạp Cu với hàm lượng tạp Cu khoảng 0,2 % - 1,5 % Năng lượng dịch đỉnh AH PH mẫu pha tạp Cu so với mẫu không pha tạp mối liên quan với hàm lượng tạp Cu Ảnh TEM phân bố kích thước mẫu NC Cd0.4Zn0.6S pha tạp Cu với hàm lượng khác nhau: (a) %; (b) 0,2 %; (c) % (a) Phân tích Rietveld giản đồ XRD NC Cd0.4Zn0.6S có hàm lượng Cu %, 0,5 % % (Các số Miller tương ứng với đỉnh nhiễu xạ pha Zb số in nghiêng); (b) Sự thay đổi tỉ phần pha Wz mẫu theo hàm lượng tạp Cu 43 44 44 45 MỤC LỤC Trang Mở đầu …………………………………………………………… Chương Vấn đề pha tạp đặc trưng quang phổ nano tinh thể bán dẫn II-VI pha tạp kim loại chuyển tiếp ……… 1.1 Vấn đề pha tạp kim loại chuyển tiếp 1.2 Đặc trưng quang phổ nano tinh thể bán dẫn II-VI pha tạp kim loại chuyển tiếp 1.2.1 Năng lượng vùng cấm nano tinh thể bán dẫn hợp kim 1.2.2 Đặc trưng quang phổ nano tinh thể bán dẫn II-VI pha tạp kim loại chuyển tiếp 1.3 Ảnh hưởng cơng suất kích thích đến phổ quang huỳnh quang 1.4 Ý tưởng nghiên cứu Kết luận chương Chương Mẫu nghiên cứu phương pháp khảo sát đặc trưng vật liệu 2.1 Giới thiệu mẫu nghiên cứu 2.2 Các phương pháp khảo sát đặc trưng vật liệu ………… 2.2.1 Hiển vi điện tử truyền qua ……………………………… 2.2.2 Quang phổ tán sắc lượng ………………………… 2.2.3 Quang phổ hấp thụ nguyên tử ………………………… 2.2.4 Nhiễu xạ tia X ………………………………………… 2.2.5 Hấp thụ quang ………………………………………… 2.2.6 Quang huỳnh quang …………………………………… Kết luận chương …………………………………………………… Chương Kết nghiên cứu tính chất hấp thụ quang huỳnh quang nano tinh thể CdxZn1-xS:Cu …………… 3.1 Kích thước cấu trúc tinh thể mẫu 3.1.1 Kích thước 3.1.2 Cấu trúc tinh thể 3.2 Ảnh hưởng tạp Cu đến đặc trưng quang phổ 6 10 10 12 22 23 25 26 26 27 27 28 28 29 31 31 33 34 34 34 37 [11] Nag A., Sapra S., Nagamani C, Sharma A., Pradhan N., Bhat S.V., Sarma D.D., 2007, A study of Mn2+ Doping in CdS Nanocrystals, Chem Mater., 19, pp 3252-3259 [12] Zhang W., Zhou X., Zhong X., 2012, One-Pot Noninjection Synthesis of Cu-Doped ZnxCd1-xS Nanocrystals with Emission Color Tunable over Entire Visible Spectrum, Inorg Chem., 51, pp 3579-3587 [13] Acharya S, Pradhan N, 2011, Insertion/Ejection of Dopant Ions in Composition Tunable Semiconductor Nanocrystals, J Phys Chem., 115, pp 19513-19519 [14] Petrov D.V., Santos B.S., 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45234529 58 Công bố khoa học Phi Van Thang, Hoang Thi Lan Huong, Tran Anh Quang, Nguyen Xuan Nghia, Nguyen Thi Thuy Lieu, 2018, Excitation-power dependent photoluminescence of undoped and Cu-doped homogeneous Cd0.5Zn0.5S nanocrystals, Những tiến Quang học, Quang tử, Quang phổ Ứng dụng X, tr 173-178 59 Những tiến Quang học, Quang tử, Quang phổ Ứng dụng X 2018 EXCITATION-POWER DEPENDENT PHOTOLUMINESCENCE OF UNDOPED AND Cu-DOPED HOMOGENEOUS Cd0.5Zn0.5S NANOCRYSTALS Phi Van Thang1, Hoang Thi Lan Huong2, Tran Anh Quang3, Nguyen Xuan Nghia4, Nguyen Thi Thuy Lieu2 Quy Nhon University, 170 An Duong Vuong, Quy Nhon, Binh Dinh Posts and Telecommunications Institute of Technology, Km10 Nguyen Trai, Thanh Xuan, Hanoi Quang Ninh High School, Quang Ninh, Quang Binh Institute of Physics, 10 Dao Tan, Ba Dinh, Hanoi E-mail: nttlieu@ptit.du.vn Abstract Excitation-power dependent photoluminescence spectra of undoped and Cu-doped homogeneous Cd0.5Zn0.5S nanocrystals have been investigated in range of excitation power from 5×10-3 to mW The existence of Cu dopant in host nanocrystals leads to a strong increase in intensity of low energy emission band in comparison to high energy emission peak The influence of excitation power on the energy position and intensity of emission peaks at high and low energies is analyzed It was found that the excitation power dependent changes in spectral characteristics of undoped and Cu-doped samples are different The intensity ratio of high energy emission peak and low energy emission band increases for Cudoped sample and decreases for undoped sample Besides the band gap renormalization phenomenon observed for the high energy emission peaks of both samples, a linear dependence of the emission energy on third root of excitation power ranging to 0.46 mW was obtained for the low energy band of Cu-doped sample, and interpreted in terms of a state filling mechanism Key words: Undoped and Cu-doped Cd0.5Zn0.5S nanocrystals, Excitation-power dependent photoluminescence, State filling, Band gap renormalization I INTRODUCTION Among the II-VI group, ZnS (Eg = 3.72 eV) and CdS (Eg = 2.42 eV) are important wide bandgap semiconductors, which have potential applications in ultraviolet (UV)-light emitting diodes, electroluminescent devices, photocatalysis, chemical and biological sensing and in imaging applications [1-6] The formation of CdxZn1-xS nanocrystals (NCs) has recently opened new opportunities to tune the optical properties from the UV to the near infrared not only by changing the size but also by varying the Cd 2+/Zn2+ ratio in the NCs [7, 8] In recent years, transition metal (TM)-doped NCs have been investigated intensively since they not simply have all advantages of NCs but also possess additional advantages such as larger Stokes shift to avoid self-absorption/energy transfer, longer excited state lifetimes, and enhanced thermal and chemical stability [9-12] Among doped NC emitters, Mn- and Cu-doped NCs are leading Contrary to Mn-doped NCs, the emission of Cu-doped NCs was mainly originated due to the transition from the conduction ISBN: 173 Advances in Optics, Photonics, Spectroscopy and Applications X 2018 band of host semiconductor to the Cu-d states [13-16] Thus, Cu-doping can provide a convenient way to control the optical properties of host semiconductor In this work, colloidal undope and Cu-doped Cd0.5Zn0.5S NCs are prepared by wet chemical method The excitation power dependent PL spectra are investigated to elucidate the influence of Cu dopant on optical properties of homogeneous Cd0.5Zn0.5S NCs Their spectroscopic characteristics are analysed in relation to the crystal structure II EXPERIMENTS Materials and chemicals Initial chemicals, including zinc stearate (Zn(St)2, 98%), cadmium oxide (CdO, 99.99%, powder), sulfur (S, 99.98%, flour), 1-octadecene (ODE, 90%), and stearic acid (SA, 90%), were purchased from Aldrich and used as received without further purification Synthesis of Cd0.5Zn0.5S NCs For the synthesis of Cd0.5Zn0.5S NCs, a mixture of S (1 mmol) and ODE (24 mmol) was stirred at 100 °C for 60 in a vessel Meanwhile, 0.5 mmol of CdO, 1.4 mmol of SA, and 60 mmol of ODE were put in a three-neck flask, which was then heated up to 280 °C for 60 in order to form a transparent Cd solution Zn solution was obtained by dissolving 0.5 mmol of Zn(St)2 in mixture of SA (0.036 mmol) and ODE (60 mmol) at 180 o C for 60 After that, S solution was swiftly injected into a reaction flask containing a half of Zn and Cd precursor solutions at 280 oC Small amounts of remaining Zn and Cd precursor solutions then were alternately injected into reaction flask The Cd0.5Zn0.5S sample was prepared with reaction time of 270 and labeled as A Synthesis of Cu-doped Cd0.5Zn0.5S NCs Typical synthetic procedure previously described for the preparation of Cd 0.5Zn0.5S was followed expect that Cu 0.2 mol% relative to Cu and Zn was added to the mixture of Cd(St)2, Zn(St)2, SA and ODE before the injection of S precursor solution Cu-doped Cd0.5Zn0.5S sample also was prepared with reaction time of 270 and denoted by B Purification of NC samples Crude solutions obtained after preparing NC samples were mixed with isopropanol (according to the ratio of 1/3 in volume) NCs were collected by using a centrifuge, which worked with speed of 15000 rpm for After purification, a part of the products in powder was used to investigate crystal structure Other parts were dispersed in toluene for checking morphology and size and spectroscopic measurments Measurements Transmission electron microscopy (TEM) images of undoped and Cu-doped Cd0.5Zn0.5S samples were recorded by using JEM 1010 and JEM 2100 microscopes (Jeol) The samples were mounted on a carbon-coated cooper-mesh grid X-ray diffraction (XRD) patterns were obtained from an X-ray diffractometer (Siemen, D5005), using a Cu Kα radiation source with λ = 1.5406 Å Optical absorption spectra were recorded with a Jasco 670 spectrometer The photoluminescence (PL) properties of nanocrystals were studied by using iHR550 spectrometers, where an He-Cd laser with a wavelength of 325 nm and with a maximum excitation power of mW was used 174 ISBN: Những tiến Quang học, Quang tử, Quang phổ Ứng dụng X III 2018 RESULTS AND DISCUSSION Fig shows TEM images of the undoped and Cu-doped Cd0.5Zn0.5S NCs They have dot-like shape and average diameter of ~ 6.5 nm, reflecting that Cu content of 0.2 mol% does not influence on the shape and size of host NCs Fig.1 TEM images of (a) sample A and (b) sample B 20 (112) (311) (110) (220) (102) 30 40 50 2 (degree) 60 (b) Lattice parameter (angstrom) Exp IZb+IWz Zb Wz (101) (100) Intensity (a.u.) (a) (002) (111) XRD patterns of samples A and B are similar For illustration, the XRD pattern of sample A is shown in Fig 2a The shoulders on both sides of diffraction peak centered at about 27° reveal the superposition of diffraction peaks of zinc blende (Zb) and wurtzite (Wz) phases in Cd0.5Zn0.5S NCs To separate the diffraction peaks corresponding to Zb and Wz phases, Rietveld refinement analysis was performed using FullProf program modified with atomic scattering factors for electrons (Wz in space group P63mc and Zb in space group F-43 m) [17, 18] The Zb phase of sample A is characterized by the diffraction peaks centered at 27.6, 45.9, and 54.4° corresponding to the Miller indices (111), (220), and (311), respectively Meanwhile, the remaining part of XRD pattern indicates the Wz phase with the diffraction peaks centered at 26.0, 27.5, 29.4, 38.2, 45.8, and 53.4°, which correspond to the Miller indices (100), (002), (101), (102), (110), and (112), respectively As displayed in Fig 2b, the obtained lattice parameters of Zb and Wz phases are in good agreement with the lattice parameters of bulk Cd0.5Zn0.5S material This confirms the homogeneous alloying of sample A Moreover, the Zb phase fraction calculated basing on the integrated intensities of diffraction peaks of Wz and Zb phases is 52% The similarity of XRD patterns of samples A and B shows the Cu content of 0.2 mol% does not influence on the composition homogeneity and phase fractions of host NCs 0.65 cWz 0.60 0.55 aZb 0.50 0.45 0.40 aWz 0.0 0.2 0.4 0.6 0.8 1.0 Composition (x) Fig.2 (a) Rietveld refinement analysis of XRD pattern, and (b) the evidence on the homogeneous alloy of sample A ISBN: 175 Advances in Optics, Photonics, Spectroscopy and Applications X 2018 The absorption and PL spectra of samples A and B are depicted in Fig 3a The Cu doping leads to a shift of the first absorption peak and high energy emission peak (labeled as H) from 2.77 to 2.85 eV, and a strong increase in the intensity of low energy emission band (labeled as L) To date, the blue shift of TM-doped A2B6 NCs is explained by the different causes: the change in NC size [19, 20] or the intrinsic reasons of TM-doped NCs like the sp-3d exchange interaction in confinement regime, strain in NC, or excess carriers [21, 22], and therefore, need the further research (b) (a) L PL intensity (a.u.) Absorbance (a.u.) L PL intensity (a.u.) Exc power To identify the optical transitions as well as the competition of radiative combination chanels in Cd0.5Zn0.5S and Cu-doped Cd0.5Zn0.5S NCs, their excitation power dependent PL spectra were investigated As seen in Fig 3b, the changes in relative intensities of emission peaks are different for samples A and B with increasing the excitation power Careful analyses of these excitation power dependent PL spectra lead to the results plotted in Figs 4a and 4b H B H L H B A A 1.0 1.5 2.0 2.5 3.0 3.5 Energy (eV) 1.5 2.0 2.5 3.0 Energy (eV) Fig.3 (a) Absorption and PL spectra, and (b) excitation power dependent PL spectra of samples A and B (b) 100 (a) 2.85 EH(A) 2.70 IL×100/(IL+IH) Emission energy (eV) 90 2.80 2.75 B 95 EH(B) 85 80 A 75 EL(B) + 0.7 eV 70 2.65 0.01 0.1 Excitation power (mW) 0.01 0.1 10 Excitation power (mW) Fig.4 (a) Emissions energies and (b) the integrated intensity ratios IL100/(IL+IH) of samples A and B as a function of excitation power 176 ISBN: Những tiến Quang học, Quang tử, Quang phổ Ứng dụng X 2018 In Fig 4a, it shows that the emission energies EH(A) and EH(B) of peaks H of samples A and B are decreased 28 and meV, respectively, as excitation power increases from 0.005 to mW The red shift of band-edge emission peaks is attributed to the band gap renormalization Remarkably, the weaker band gap renormalization for sample B is due to the appearance of new radiative recombination chanel through Cu centers, leading to a decrease of the number of electron and hole located in conduction and valence bands of Cd0.5Zn0.5S NCs As could be seen in Fig 4b, with increasing excitation power from 0.005 to mW, the integrated intensity ratio IL100/(IL+IH) decreases from 94 to 69 % for sample A, meanwhile this ratio changes only from 97 to 91 % for sample B This supports the above suggestion Differently from the high energy emission peak H, the low energy emission band L of sample B increases ~ 24 meV as excitation power increases (Fig 4a) The insert in Fig 5a shows clearly the gradual shift of emission band L of sample B towards high energy side when increasing excitation power As above mentioned, the XRD analysis shows the coexistence of Zb and Wz phases in samples A and B The simultaneous appearance of band-edge and dopant emissions reveals that the carrier confinement regime in Cu-doped Cd0.5Zn0.5S NCs is quasi type-II 0.005 mW 0.46 mW mW (b) 1.99 Emission energy (eV) Normalized intensity (a.u.) (a) 1.6 2.0 2.4 Excitation power (mW) 1.98 1.97 1.96 1.95 0.0 0.5 1.0 1.5 Excitation power1/3 (mW)1/3 Fig (a) Low energy emission band L of Cu-doped Cd0.5Zn0.5S NCs at the different excitation powers; and (b) its emission energy versus the cubic root of excitation power In order to elucidate the nature of emission band L as excitation power increases, Fig 5b presents the energy position of this band as a function of the cubic root of excitation power The linear dependence for excitation power value up to 0.46 mW indicates the type-II nature of emission band L Thus, the emission band L is originated from the spatially indirect transition across Zb domain/Wz domain interface At higher excitation powers, the state filling results in the deviation of emission energy of this band from the linear relation In this case, the emission band L contains the spatially indirect transition across Zb domain/Wz domain interface, and the spatially direct transition from the excited state in conduction band to the Cu2+ state in both Zb and Wz domains ISBN: 177 Advances in Optics, Photonics, Spectroscopy and Applications X IV 2018 CONCLUSION Colloidal undoped and Cu-doped Cd0.5Zn0.5S NCs were prepared by wet chemical method at 280 oC for 270 Rietveld refinement analysis indicates that the samples are homogeneous alloy, and have the Zb phase fraction of 52 % The Cu doping leads to a strong increase in the intensity of low energy emission band The excitation power dependent PL was investigated in order to identify the nature of optical transitions as well as the competition of radiative recombination chanels in undoped and Cu-doped samples The confinement regime for the carriers in Cu-doped Cd0.5Zn0.5S NCs is quasi type-II The increase of excitation power leads to the band gap renormalization and band bending for host NCs At excitation power higher than 0.46 mW, the low energy emission band of Cudoped sample contains the spatially indirect transition across Zb domain/Wz domain interface, and the spatially direct transition from the excited state in conduction band to the Cu2+ state in both Zb and Wz domains The results provided an insight into the fundamental understanding of the optical transitions in Cu-doped ternary semiconductor NCs with coexistence of Zb and Wz structure phases V ACKNOWLEDGMENTS This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.02-2017.54 REFERENCES D.R Larson, W.R Zipfel, R.M Williams, S.W Clark, M.P Bruchez, F.W Wise, W.W Webb, Science, Vol 300, 2003, pp 1434-1436 P.O Anikeeva, J.E Halpert, M.G Bawendi, V Bulovic, Nano Lett Vol 9, 2009, pp 25322536 M Afzaal, P O‘Brien, J Mater Chem Vol 16, 2006, pp 1597-1602 B.N Pal, Y Ghosh, S Brovelli, R Loacharoensuk, V Klimov, J.A Hollingsworth, H Htoon, Nano Lett Vol 12, 2012, pp 331-336 A Aboulaich, D Billaud, M Abyan, L Balan, J.-J Gaumet, G Medjahdi, J Ghanbaja, R Schneider, ACS Appl Mater Interfaces Vol 4, 2012, pp 2561-2569 H Labiadh, T Ben Chaabane, L Balan, N Becheik, G Medjahdi, R Schneider, Appl Catal B: Environ Vol 144, 2014, pp 29-35 E Busby, A Thibert, et al., Chem Phys Lett Vol 573, 2013, pp 56-62 S Bhandari, R Begum, A Chattopadhyay, RSC Adv Mater Vol 3, 2013, pp 2885-2888 D.J Norris, A.L Efros, S.C Erwin, Science Vol 309, 2008, pp 1776-1779 10 P Wu, X.P Yan, Chem Soc Rev Vol 42, 2013, pp 5489-5521 11 S Jana, G Manna, B.B Srivastava, N Pradhan, Small Vol 9, 2013, pp 3753-3758 12 S Liu, X Su, Anal Methods Vol 5, 2013, pp 4541-4548 13 B.B Srivastava, S Janan, N Pradhan, J Am Chem Soc Vol 133, 2011, pp 1007-1015 14 R Viswanatha, S Brovelli, et al., Nano Lett Vol 11, 2011, pp 4753-4758 15 S Brovelli, C Galland, R Viswanatha, V.I Klimov, Nano Lett Vol 12, 2012, pp.4372-4379 16 Z Zhang, D Li, R Xie, W Wang, Angew Chem Vol 125, 2013, pp 5156-5159 17 V Kumar, S Kumari, et al., Adv Mater Lett Vol 6, 2015, pp 139-147 18 J Li, B Kempken, V Dzhagan, D.R.T Zahn, J Grzelak, S Mackowski, J Parisi, J KolnyOlesiak, CrystEngComm Vol 17, 2015, pp 5634-5643 19 R.S Kurma, V.Veeravazhuthi, N Muthukumarasamy, M Thambidurai, D.V Sankar, Superlattices and Microstructures Vol 86, 2015, pp 552-558 20 K Hadasa, G Yellaiah, M Nagabhushanam, Optik Vol 125, 2014, pp 6602-6608 21 I Devadoss, S Muthukumaran, Physica E Vol 72, 2015, pp 111-119 22 I Devadoss, S Muthukumaran, Mater Sci Semicond Proc Vol 41, 2016, pp 282-290 178 ISBN: