Tổng hợp và nghiên cứu tính chất quang của chấm lượng tử zns pha tạp mn bọc phủ thiolglycolic axit

ỦY BAN NHÂN DÂN THÀNH PHỐ HỒ CHÍ MINH SỞ KHOA HỌC VÀ CƠNG NGHỆ THÀNH ĐỒN TP HỒ CHÍ MINH TRUNG TÂM PHÁT TRIỂN KHOA HỌC VÀ CÔNG NGHỆ TRẺ CHƯƠNG TRÌNH KHOA HỌC VÀ CƠNG NGHỆ CẤP THÀNH PHỐ BÁO CÁO TỔNG HỢP KẾT QUẢ NHIỆM VỤ NGHIÊN CỨU KHOA HỌC VÀ CÔNG NGHỆ TỔNG HỢP VÀ NGHIÊN CỨU TÍNH CHẤT QUANG CỦA CHẤM LƯỢNG TỬ ZnS PHA TẠP Mn BỌC PHỦ THIOLGLYCOLIC AXIT Cơ quan chủ trì nhiệm vụ: Trung tâm Phát triển Khoa học Công nghệ Trẻ Chủ nhiệm nhiệm vụ: ThS Nguyễn Thành Phương Thành phố Hồ Chí Minh - 2019 ỦY BAN NHÂN DÂN THÀNH PHỐ HỒ CHÍ MINH SỞ KHOA HỌC VÀ CƠNG NGHỆ THÀNH ĐỒN TP HỒ CHÍ MINH TRUNG TÂM PHÁT TRIỂN KHOA HỌC VÀ CƠNG NGHỆ TRẺ CHƯƠNG TRÌNH KHOA HỌC VÀ CÔNG NGHỆ CẤP THÀNH PHỐ BÁO CÁO TỔNG HỢP KẾT QUẢ NHIỆM VỤ NGHIÊN CỨU KHOA HỌC VÀ CƠNG NGHỆ TỔNG HỢP VÀ NGHIÊN CỨU TÍNH CHẤT QUANG CỦA CHẤM LƯỢNG TỬ ZnS PHA TẠP Mn BỌC PHỦ THIOLGLYCOLIC AXIT Chủ nhiệm nhiệm vụ: (ký tên) Chủ tịch Hội đồng nghiệm thu (Ký ghi rõ họ tên) Nguyễn Thành Phương Cơ quan chủ trì nhiệm vụ Đồn Kim Thành THÀNH ĐỒN TP HỒ CHÍ MINH TRUNG TÂM PHÁT TRIỂN KHOA HỌC VÀ CÔNG NGHỆ TRẺ CỘNG HOÀ XÃ HỘI CHỦ NGHĨA VIỆT NAM Độc lập - Tự - Hạnh phúc TP HCM, ngày 17 tháng 04 năm 2019 BÁO CÁO THỐNG KÊ KẾT QUẢ THỰC HIỆN NHIỆM VỤ NGHIÊN CỨU KH&CN I THÔNG TIN CHUNG Tên nhiệm vụ: TỔNG HỢP VÀ NGHIÊN CỨU TÍNH CHẤT QUANG CỦA CHẤM LƯỢNG TỬ ZnS PHA TẠP Mn BỌC PHỦ THIOLGLYCOLIC AXIT Thuộc: Chương trình/lĩnh vực (tên chương trình/lĩnh vực): Vườn ươm Sáng tạo Khoa học Cơng nghệ trẻ Chủ nhiệm nhiệm vụ: Họ tên: Nguyễn Thành Phương Ngày, tháng, năm sinh: 03/04/1984 Nam/ Nữ: Nam Học hàm, học vị: Thạc sĩ Chức danh khoa học: Chức vụ Điện thoại: Tổ chức: (+84 - 028) 38968641 Nhà riêng: Mobile: 0938196184 Fax: E-mail: phuongnt@hcmute.edu.vn Tên tổ chức công tác: Khoa In & Truyền thông – Trường Đại học Sư phạm Kỹ thuật TP Hồ Chí Minh Địa tổ chức: Số 1, Võ Văn Ngân, Phường Linh Chiểu, Quận Thủ Đức Địa nhà riêng: Số 9.13, Khối A2, Chung cư Hiệp Bình Phước – Tam Bình, Đường Gị Dưa, Quận Thủ Đức Tổ chức chủ trì nhiệm vụ: Tên tổ chức chủ trì nhiệm vụ: Trung tâm Phát triển Khoa học Công nghệ trẻ Điện thoại: (028) 38 233 363 - (028) 38 230 780Fax: E-mail: khoahoctre@gmail.com Website: http:// khoahoctre.com.vn Địa chỉ: Số 1, Phạm Ngọc Thạch, P.Bến Nghé, Quận 1, TP.Hồ Chí Minh Họ tên thủ trưởng tổ chức: Đoàn Kim Thành Số tài khoản: 3713.0.1083277.00000 Kho bạc Nhà nước/Ngân hàng: Kho bạc Nhà nước Quận Thành phố Hồ Chí Minh Tên quan chủ quản đề tài: Sở Khoa học Công nghệ Tp HCM II TÌNH HÌNH THỰC HIỆN Thời gian thực nhiệm vụ: - Theo Hợp đồng ký kết: từ 20 tháng năm 2018 đến 20 tháng năm 2019 - Thực tế thực hiện: từ 20 tháng năm 2018 đến 20 tháng năm 2019 - Được gia hạn (nếu có): - Lần từ tháng… năm… đến tháng… năm… - Lần … Kinh phí sử dụng kinh phí: a) Tổng số kinh phí thực hiện: 80 tr.đ, đó: + Kính phí hỗ trợ từ ngân sách khoa học: 80 tr.đ + Kinh phí từ nguồn khác: tr.đ b) Tình hình cấp sử dụng kinh phí từ nguồn ngân sách khoa học: Số TT Theo kế hoạch Thời gian Kinh phí (Tháng, năm) (Tr.đ) Trong vịng ngày 40 hợp đồng ký Khi nộp báo cáo tiến 24 độ tháng Đề tài nghiệm 16 thu hợp đồng lý Thực tế đạt Thời gian Kinh phí (Tháng, năm) (Tr.đ) 6/2018 40 Ghi (Số đề nghị toán) 11/2018 24 5/2019 Đang làm hồ sơ toán c) Kết sử dụng kinh phí theo khoản chi: Đối với đề tài: Đơn vị tính: Triệu đồng Số TT Nội dung khoản chi Trả công lao động (khoa học, phổ thông) Nguyên, vật liệu, lượng Chi khác Tổng cộng - Lý thay đổi (nếu có): Theo kế hoạch Tổng NSKH 64,8102 64,8102 5,150 5,150 10,0398 10,0398 80 80 Thực tế đạt Nguồn Tổng khác 64,8102 NSKH 64,8102 Nguồn khác 0 5,150 5,150 0 10,0398 10,0398 0 80 80 Các văn hành q trình thực đề tài/dự án: (Liệt kê định, văn quan quản lý từ công đoạn xét duyệt, phê duyệt kinh phí, hợp đồng, điều chỉnh (thời gian, nội dung, kinh phí thực có); văn tổ chức chủ trì nhiệm vụ (đơn, kiến nghị điều chỉnh có) Số TT … Số, thời gian ban hành văn Tên văn Ghi Tổ chức phối hợp thực nhiệm vụ: Số TT Tên tổ chức đăng ký theo Thuyết minh Tên tổ chức tham gia thực Nội dung tham gia chủ yếu Sản phẩm chủ yếu đạt Ghi chú* - Lý thay đổi (nếu có): Cá nhân tham gia thực nhiệm vụ: (Người tham gia thực đề tài thuộc tổ chức chủ trì quan phối hợp, không 10 người kể chủ nhiệm) Số TT Tên cá nhân đăng ký theo Thuyết minh Nguyễn Thành Phương Tên cá nhân tham gia thực Nguyễn Thành Phương Nội dung tham gia Nội dung 1: Tổng hợp chấm lượng tử ZnS pha tạp Mn2+ (ZnS:Mn2+ QDs) bọc phủ TGA Sản phẩm chủ yếu đạt Báo cáo phân tích, báo đăng tạp chí ISI Nội dung 4: Viết báo đăng tạp chí chuyên ngành thuộc danh mục ISI, viết báo cáo tổng kết đề tài Bùi Tấn Phúc Bùi Tấn Phúc Nội dung 2: Nghiên cứu hình thái, cấu trúc chấm lượng tử ZnS:Mn2+ bọc phủ TGA Báo cáo phân tích Lâm Quang Vinh Lâm Quang Vinh Nội dung 3: Nghiên cứu tính chất quang chấm lượng tử ZnS:Mn2+ bọc phủ TGA Báo cáo phân tích - Lý thay đổi ( có): Ghi chú* Tình hình hợp tác quốc tế: Theo kế hoạch Số TT (Nội dung, thời gian, kinh phí, địa điểm, tên tổ chức hợp tác, số đoàn, số lượng người tham gia ) Thực tế đạt (Nội dung, thời gian, kinh phí, địa điểm, tên tổ chức hợp tác, số đoàn, số lượng người tham gia ) Ghi chú* - Lý thay đổi (nếu có): Tình hình tổ chức hội thảo, hội nghị: Số TT Theo kế hoạch Thực tế đạt (Nội dung, thời gian, kinh phí, địa điểm ) (Nội dung, thời gian, kinh phí, địa điểm ) Nội dung: Chế tạo chấm lượng tử ZnS:Mn2+ bọc phủ thiolglycolic acid Nội dung: Ứng dụng chấm lượng tử ZnS:Mn2+ mực in Thời gian: đầu tháng 04/2019, kinh phí triệu đồng, địa điểm: Khoa In & Truyền thông, Đại học Sư phạm Kỹ thuật TP HCM Thời gian: 03/05/2019, kinh phí triệu đồng, địa điểm: Khoa In & Truyền thông, Đại học Sư phạm Kỹ thuật TP HCM Ghi chú* - Lý thay đổi (nếu có): Tóm tắt nội dung, công việc chủ yếu: (Nêu mục 15 thuyết minh, không bao gồm: Hội thảo khoa học, điều tra khảo sát nước nước ngồi) Số TT Các nội dung, cơng việc chủ yếu (Các mốc đánh giá chủ yếu) Nội dung 1: Xây dựng thuyết minh đề tài nghiên cứu Nội dung 2: Tổng hợp chấm lượng tử ZnS pha tạp Mn2+ (ZnS:Mn2+ QDs) bọc phủ TGA  Công việc 1: Xây dựng quy trình chế tạo ZnS:Mn2+ QDs bọc phủ TGA Thời gian (Bắt đầu, kết thúc - tháng … năm) Theo kế Thực tế đạt hoạch 1/2018 1/2018 1/2018 – 6/2018 1/2018 – 6/2018 Người, quan thực Nguyễn Thành Phương Bùi Tấn Phúc  Công việc 2: Chế tạo ZnS:Mn2+ QDs theo thông số: nồng độ Mn2+ pha tạp, tỷ lệ Zn2+/S2- lượng chất bao TGA Nội dung 3: Nghiên cứu hình thái, cấu trúc chấm lượng tử ZnS:Mn2+ bọc phủ TGA 6/2018 6/2018 Lâm Quang Vinh 7/2018 – 8/2018 7/2018 – 8/2018 Nguyễn Thành Phương 8/2018 – 12/2018 8/2018 – 12/2018 Nguyễn Thành Phương Cơng việc: Phân tích giản đồ nhiễu xạ tia X ZnS:Mn2+ QDs khảo sát sát ảnh TEM Nội dung 4: Nghiên cứu tính chất quang chấm lượng tử ZnS:Mn2+ bọc phủ TGA Công việc: Nghiên cứu tính chất quang ZnS:Mn2+ QDs phương pháp quang phổ UVVis, quang huỳnh quang (PL), kích thích huỳnh quang (PLE), huỳnh quang phân giải thời gian, FTIR Nội dung 5: Viết báo cáo tổng kết đề tài  Công việc 1: Viết báo đăng tạp chí chun ngành thuộc danh mục ISI  Cơng việc 2: Viết báo cáo tổng kết đề tài - Lý thay đổi (nếu có): III SẢN PHẨM KH&CN CỦA NHIỆM VỤ Sản phẩm KH&CN tạo ra: a) Sản phẩm Dạng I: Số TT Tên sản phẩm tiêu chất lượng chủ yếu Đơn vị đo Số lượng Thực tế đạt Theo kế hoạch Điều khiển kích thước chấm lượng tử ZnS:Mn2+ theo lượng TGA khác Khảo sát mẫu Kích thước < theo lượng TGA 20nm, phát khác quang 590 nm Kích thước 7,5 – 18 nm, phát quang 590 nm Chấm lượng tử ZnS:Mn2+ có cấu trúc tinh thể xác định Khảo sát mẫu Cấu trúc lập phương lục giác ZnS:Mn2+ có cấu trúc lập phương lục giác Chấm lượng tử ZnS:Mn2+, hấp thụ ánh sáng khoảng 290 – 300 nm, phát quang bước sóng 590 nm Khảo sát mẫu Đỉnh hấp thụ khoảng 290 300 nm, phát huỳnh quang 590 nm ZnS:Mn2+ có đỉnh hấp thụ UV-vis khoảng 277 – 315 nm, phát quang 590 nm - Lý thay đổi (nếu có): b) Sản phẩm Dạng II: Số TT Tên sản phẩm Quy trình chế tạo chấm lượng tử ZnS:Mn2+ nhiệt độ phòng Báo cáo phân tích, đánh giá số liệu thực nghiệm - Lý thay đổi (nếu có): Yêu cầu khoa học cần đạt Theo kế hoạch Thực tế đạt Dạng sơ đồ khối, kèm theo điều kiện kỹ thuật, độ ổn định cao, điều khiển kích thước, phân bố kích thước hẹp từ 15 – 20 nm Đánh giá chuyên sâu số liệu thực nghiệm thu dựa tảng khoa học từ báo đăng tạp chí chun ngành có uy tín Ghi Dạng sơ đồ khối, kèm theo điều kiện kỹ thuật Phân bố kích thước từ 7,5 – 18 nm Quy mơ phịng thí nghiệm Báo cáo đánh giá chuyên sâu số liệu thực nghiệm thu, 01 báo đăng tạp chí Journal of luminescence, thuộc danh mục SCI 01 báo tham khảo thuộc danh mục SCI, IF > 2.7 c) Sản phẩm Dạng III: Số TT Tên sản phẩm Bài báo nghiên cứu Yêu cầu khoa học cần đạt Theo Thực tế kế hoạch đạt Số lượng, nơi công bố (Tạp chí, nhà xuất bản) 01 báo đăng 01 báo đăng tạp chí thuộc danh tạp chí thuộc mục ISI, IF >2 danh mục ISI SCI, IF >2.7 Journal of Luminescence, Elsevier - Lý thay đổi (nếu có): d) Kết đào tạo: Số TT Cấp đào tạo, Chuyên ngành đào tạo Thạc sỹ Tiến sỹ Số lượng Theo kế hoạch Thực tế đạt Ghi (Thời gian kết thúc) - Lý thay đổi (nếu có): đ) Tình hình đăng ký bảo hộ quyền sở hữu công nghiệp: Số TT Tên sản phẩm đăng ký Kết Theo kế hoạch Thực tế đạt Ghi (Thời gian kết thúc) - Lý thay đổi (nếu có): e) Thống kê danh mục sản phẩm KHCN ứng dụng vào thực tế Số TT Tên kết ứng dụng Thời gian Địa điểm (Ghi rõ tên, địa nơi ứng dụng) Kết sơ 2 Đánh giá hiệu nhiệm vụ mang lại: a) Hiệu khoa học công nghệ: (Nêu rõ danh mục công nghệ mức độ nắm vững, làm chủ, so sánh với trình độ cơng nghệ so với khu vực giới…)  Mở hướng nghiên cứu việc tạo sản phẩm khoa học cơng nghệ mang tính liên ngành Vật lý – Hóa học – Khoa học & Cơng nghệ Vật liệu – Ngành Công nghệ Kỹ thuật In  Bên cạnh đó, kết nghiên cứu cịn đóng góp vào lĩnh vực nghiên cứu mà giới nghiên cứu – lĩnh vực in điện tử (Printed lectronic) b) Hiệu kinh tế xã hội: (Nêu rõ hiệu làm lợi tính tiền dự kiến nhiệm vụ tạo so với sản phẩm loại thị trường…) Trong tương lai loại màng mỏng điện phát quang dần thay loại bảng dẫn, biển quảng cáo sử dụng đèn huỳnh quang Hơn nữa, loại bao bì thơng minh, pin mặt trời, loại thẻ nhận dạng qua sóng radio (RFID) sản xuất quy mô lớn thông qua việc kết hợp Công nghệ vật liệu với ngành Cơng nghệ Kỹ thuật in Tình hình thực chế độ báo cáo, kiểm tra nhiệm vụ: Số TT I Thời gian thực Nội dung Ghi (Tóm tắt kết quả, kết luận chính, người chủ trì…) Báo cáo tiến độ Nội dung 1: Xây dựng thuyết minh đề tài nghiên cứu 4/12/2018 Bản thuyết minh đề tài Nội dung 2: Tổng hợp chấm lượng tử ZnS pha tạp Mn2+ (ZnS:Mn2+ QDs) bọc phủ TGA Quy trình chế tạo ZnS:Mn2+ QDs Nội dung 3: Nghiên cứu hình thái, cấu trúc chấm lượng tử ZnS:Mn2+ bọc phủ TGA Giản đồ nhiễu xạ tia X, ảnh TEM Nội dung 4: Nghiên cứu tính chất quang chấm lượng tử ZnS:Mn2+ bọc phủ TGA Nội dung 5: Viết báo cáo tổng kết đề tài Phổ UV-vis, PL, PLE Kết báo cáo tổng kết đề tài Chủ nhiệm đề tài (Họ tên, chữ ký) Nguyễn Thành Phương Thủ trưởng tổ chức chủ trì (Họ tên, chữ ký đóng dấu) CHƯƠNG KẾT LUẬN VÀ HƯỚNG PHÁT TRIỂN ĐỀ TÀI Kết luận Đề tài đạt số kết sau: Đã chế tạo thành công chấm lượng tử ZnS pha tạp Mn2+ (ZnS:Mn2+ QDs) phương pháp kết tủa hóa học nhiệt độ 80oC, mơi trường khí Chấm lượng tử ZnS:Mn2+ có cấu trúc lập phương zinc-blend cấu trúc hexagonal wurtzite Kết khảo sát ảnh TEM cho thấy ZnS:Mn2+ QDs có dạng hình cầu với kích thước hạt khoảng 7,5 nm Tỷ lệ mol [S2-]/[Zn2+] ảnh hưởng đến cường độ phát xạ ion Mn2+ 4T1 – 6A1, tỷ lệ mol [S2-]/[Zn2+] > 1,5:1 dẫn đến mở rộng vùng phát xạ màu đỏ - cam phía bước sóng 700 nm hình thành cặp Mn2+-Mn2+ Tỷ lệ cường độ PL tương đối IOE/IBE tăng tăng lượng chất bao TGA tăng đạt giá trị lớn (tối ưu) thể tích VTGA = ml Sự dịch chuyển đỏ nhẹ đỉnh phát xạ Mn2+ 4T1 – 6A1 từ 588 đến 593 nm xuất nhiệt độ nung tăng từ 100 – 500oC Tại nhiệt độ nung 500oC pha MnS hình thành bên tinh thể mạng chủ ZnS Các ZnS:Mn2+ QDs phân tán dung dịch PVA có tiềm ứng dụng chế tạo mực in phun loại màng hình phát sáng Hướng phát triển đề tài  Xây dựng công thức mực in chấm lượng tử ZnS:Mn2+ QDs/PVA để chế tạo loại màng mỏng phát kỹ thuật in lụa công nghệ in phun  Ứng dụng in chống giả phát huỳnh quang cách pha tạp với ion kim loại khác Cu, Mn vào mạng 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Semiconductor Physics, Quantum Electronics & Optoelectronics 15 117 81 Journal of Luminescence 203 (2018) 533–539 Contents lists available at ScienceDirect Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin Energy transfer in poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots T ⁎ Thanh Phuong Nguyena,b, , Quang Vinh Lamc, Thi Bich Vud,e a Faculty of Graphic Arts and Media, HCMC University of Technology and Education, No Vo Van Ngan Street, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City 700000, Vietnam b University of Science, Viet Nam National University Ho Chi Minh City, No 227 Nguyen Van Cu Street., Ward 4, District 5, Ho Chi Minh City 700000, Vietnam c Viet Nam National University Ho Chi Minh City, Linh Trung Ward, Thu Duc District, Ho Chi Minh City 700000, Vietnam d Institute of Physics, Viet Nam Academy of Science and Technology, No 10, Dao Tan, Thu Le, Ba Dinh, Ha noi 100000, Vietnam e Duy Tan University, No 254 Nguyen Van Linh Street, Thanh Khe District, Da Nang City, Vietnam A R T I C LE I N FO A B S T R A C T Keywords: Energy transfer Mn2+-doped ZnS Quantum dots Photoluminescence Poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped ZnS quantum dots (PVA-ZnS:Mn2+ QDs) synthesized at 80 °C in air The structural property was investigated using X-ray powder diffraction (XRD) The XRD analysis shows that the ZnS:Mn2+ QDs possessed a zinc blende structure and the complexes of ZnS:Mn2+ QDs with PVA molecules have been formed The photoexcitation energy transfer is found and investigated between PVA molecules and ZnS:Mn2+ QDs using characterization techniques such as Fourier transform infrared spectroscopy (FTIR), UV–vis absorption spectroscopy, photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy The studied results show the photoluminescence enhancement of the Mn2+ 4T1(G) – 6A1(S) emission intensity is due to the efficient energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers Moreover, Förster resonance energy transfer (FRET) efficiency from PVA molecules to the Mn2+ center within PVA-ZnS:Mn2+ QDs is about 20.28% Introduction Semiconductor quantum dots (QDs) have attracted great interest in recent years due to their unique optical properties and potential applications Among II-VI semiconductors, zinc sulfide (ZnS) is relatively a non-toxic material when compared to Cd-based QDs ZnS has a wide direct bandgap of 3.6 eV, a small exciton Bohr radius of 2.5 nm [1] and particularly suitable as a host material for a large variety of luminescent ions such as Ag+, Cu2+, Mn2+, Eu3+, Sm3+, Tb3+ Recently, these semiconductor QDs have been systematically investigated, particularly Mn2+ doped ZnS quantum dots (ZnS:Mn2+ QDs), and have attained many successes although many debates still exist Additionally, the ZnS:Mn2+ QDs can be applied in a variety of fields such as optoelectronics [2–5], fluorescent ink [6] and fluorescent labeling agents [7,8] In particular, the hybrid polymer-semiconductor quantum dots are becoming increasingly attractive because of a large number of applications in thin film electroluminescent (EL) devices [3,5] Recently, the poly(vinyl alcohol) (PVA)-capped ZnS:Mn2+ QDs [9–12], poly(vinyl pyrrolidone) (PVP)-capped ZnS and PVP-capped ZnS:Mn2+ QDs [13] have attracted great attention Poly(vinyl alcohol) (PVA) is chosen as a good host material for QDs due to its excellent thermo-stability, transparency over the whole visible spectrum, chemical resistance, high mechanical strength and good adhesion to hydrophilic surfaces Additionally, hybrid ZnS:Mn2+ quantum dot-PVA systems have the inherent characteristics of PVA polymer matrices and unique optical of ZnS:Mn2+ QDs [12,14] However, most of the previous work on PVA-encapsulated Mn2+doped ZnS QDs is focused on understanding and solving the tasks of optimum Mn2+ doping content, PVA concentration and thermal stability of PVA-capped ZnS:Mn2+ nanoparticles [9–12] Viswanath and coworkers [9] reported that the PL color from the polyvinyl alcohol (PVA) capped Mn2+ doped ZnS nanocrystals can be tuned from UV to near infrared (IR) region Very recently, Thai et al [12] studied the effect of PVA on the photoluminescence enhancement of Mn2+ ions in ZnS:Mn2+/PVA nanoparticles Besides, Kumar et al [13] indicated the process of energy transfer from the poly(vinyl pyrrolidone) (PVP) surface adsorbate to the dopant Mn2+ ions in ZnS nanocrystals resulting in efficient orange-red emission Anni and co-worker [15] demonstrated ⁎ Corresponding author at: Faculty of Graphic Arts and Media, HCMC University of Technology and Education, No Vo Van Ngan Street, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City 700000, Vietnam E-mail address: phuongnt@hcmute.edu.vn (T.P Nguyen) https://doi.org/10.1016/j.jlumin.2018.07.010 Received May 2018; Received in revised form 18 June 2018; Accepted July 2018 Available online 06 July 2018 0022-2313/ © 2018 Elsevier B.V All rights reserved Journal of Luminescence 203 (2018) 533–539 T.P Nguyen et al 2.5 Characterization efficient Förster resonant energy transfer from a blue-emitting conjugated polymer to colloidal CdSe/ZnS core/shell quantum dots in hybrid films Moreover, to the best our knowledge, there are not any reports that clearly studied the energy transfer process from the PVA capping agent to Mn2+ luminescent centers in ZnS:Mn2+ quantum dots Thus, in this work, the structure and photoluminescence properties of the poly(vinyl alcohol)-encapsulated ZnS:Mn2+ QDs were systematically investigated and the resonance energy transfer mechanism was also discussed in detail In this study, the structure of the quantum dots was studied by the X-ray diffraction method (XRD) on Phillips X′pert XRD powder diffractometer using a radiation Cu-Kα with 1.5406 Ǻ wavelength, with 2θ from 10° to 60° The particle shape and size were studied using a JEM1010-JEOL transmission electron microscope (TEM) The FTIR spectra of the QDs were recorded with Shimadzu spectrophotometer in the range of 4000–400 cm−1 UV-Visible absorption spectra of samples were obtained using a Model PB-10 spectrophotometer after ultrasonification in de-ionized water and PVA solution Photoluminescence (PL) and photoluminescence excitation (PLE) measurements were obtained on MS-257 Oriel, FL3-22 spectrometers, respectively, using the excitation wavelength 325 nm of He-Cd laser and XFOR-450 xenon lamp All the observations were taken at room temperature Experiments 2.1 Materials Zinc acetate dihydrate (Zn(CH3COO)2·2H2O, 98%), manganese (II) chloride tetrahydrate (MnCl2·4H2O, 98%) and sodium sulfide nonahydrate (Na2S·9H2O, 98%) were purchased from Aldrich Thiolglycolic acid (TGA, HSCH2COOH, > 98%) was obtained from Merk Poly(vinyl alcohol) (PVA) (Aldrich, MW: 93,500 g/mol)) was used as the polymer matrix and stabilizer to prevent QDs agglomeration De-ionized water was used in all experiments Results and discussion 3.1 Structural and morphological properties The XRD patterns of pure PVA powders, ZnS:Mn2+ QDs, and PVAZnS:Mn2+ QDs are shown in Fig As can be seen in Fig 1(a), the three major diffraction peaks are located at 2θ = 28.7°, 47.7° and 56.4° corresponding to the lattice planes (111), (220), and (311) of cubic zincblende structure [3], which is also consistent with the standard card (JCPDS No 005–0566) No diffraction peaks from Mn2+-related impurity phase were observed in the XRD patterns, indicating that the low Mn2+ content has no obvious influence on the structure of the ZnS host For the pure PVA powders, a strong diffraction peak at 19.5° was observed in Fig 1(b), indicating PVA’s semi-crystalline nature [12] For the PVA-ZnS:Mn2+ QDs (Fig 1(c)), the diffraction peak of PVA was shown at 13.6°, while the peaks of (111), (220), and (311) belong to the cubic zinc-blende structure of ZnS:Mn2+ QDs The decrease of the PVA crystalline degree and the shift of XRD peak at lower Bragg’s angle at 13.6° indicate are due to the interaction between PVA chains and the ZnS:Mn2+ QDs The result indicates that the complexes of ZnS:Mn2+ QDs with PVA molecules have been formed (PVA-ZnS:Mn2+ QDs) Moreover, Murugadoss et al [16] reported that the decrease of the intermolecular interaction of PVA chains due to the embedment of ZnS:Mn2+ nanoparticles in PVA matrix would result in decreasing the crystalline degree of PVA The crystallite sizes were calculated according to the Debye – Scherrer’s Eq (1) [9] 2.2 Synthesis of Mn2+-doped ZnS quantum dots Colloidal Mn2+-doped ZnS quantum dots (ZnS:Mn2+ QDs) were synthesized in the air by using thiolglycolic acid (TGA) as a stabilizer In the procedure, 0.2 M of Zn(CH3COO)2·2H2O and 0.09 M of MnCl2·4H2O in 50 ml de-ionized water were dissolved together under vigorously stirring at 80 °C for 30 Subsequently, ml of thioglycolic acid (TGA = HSCH2COOH) was injected into the solution After 60 min, 0.2 M of Na2S·9H2O ([S2-]/[Zn2+] = 1:1) was dissolved in 25 ml of de-ionized water and added to the above solution The clear colloidal solution was formed immediately During the reaction process, the mixture was continuously stirred for 30 under air atmosphere at 80 °C The colloidal solution was kept at room temperature for 24 h The obtained precipitate was then isolated by centrifuging at 6000 rpm and washed several times using de-ionized water and ethanol Finally, the wet precipitate was dried for 10 h at 100 °C in an air atmosphere for further analysis 2.3 Preparation of PVA encapsulated ZnS:Mn2+ QDs (PVA-ZnS:Mn2+ QDs) In order to investigate the energy transfer process from the PVA capping agent to Mn2+ luminescent centers, the ZnS:Mn2+ QDs were encapsulated by PVA molecules (PVA-ZnS:Mn2+ QDs) First, the PVA solution (4.5 × 10−5 M) was prepared by dissolving 0.21 g of PVA in 50 ml of de-ionized water The complex solution of PVA/Zn2+ = 3×10−4 molar ratio was then stirred at 80 °C for h until completely soluble Then, 50 ml of ZnS:Mn2+ QDs aqueous solution which contained 0.22 g of ZnS:Mn2+ QD powders per 100 ml of de-ionized water was added into the above PVA/Zn2+ aqueous solution The mixture was continuously stirred for h under air atmosphere at 80 °C The obtained precipitate was then isolated by centrifuging at 6000 rpm and dried for 10 h at 100 °C in an air atmosphere for further analysis 2.4 Preparation of ZnS:Mn2+ QDs/PVA solution (ZnS:Mn2+ QDs/PVA) In the similar procedure, 0.02 g of ZnS:Mn2+ QDs powder was dispersed in 20 ml of 5.4 × 10−4 M PVA aqueous solution and 20 ml of de-ionized water (ZnS:Mn2+ QDs/PVA), respectively The colloidal solutions (1 g/l) were continuously stirred for h under air atmosphere at 80 °C and then sonicated for h to obtain a maximum dispersion Fig XRD spectra of (a) ZnS:Mn2+ QDs (b) pure PVA and (c) PVA-ZnS:Mn2+ QDs 534 Journal of Luminescence 203 (2018) 533–539 T.P Nguyen et al Fig TEM images of (a) ZnS:Mn2+ QDs and (b) PVA-ZnS:Mn2+ QDs D= 0.9λ βhkl cos θ group at 2935 cm−1 and the C˭O stretching band from acetate group at 1726 cm−1 [17] According to the Reference [18,19], the vibrational band at about 1090 cm−1, related to carboxyl stretching band (C-O), is mostly attributed to the crystallinity of the PVA As can be seen in Fig 3(b), the broad absorption bands at about 3387 cm−1 correspond to –OH group vibration which indicates the existence of absorbed water molecules on the surface of ZnS:Mn2+ QDs Besides, the narrow bands at 1132 and 896 cm−1 are due to the Zn-S stretching vibration [16,20] while the peaks at 777 and 706 cm−1 are due to the Mn-O-Mn vibration [21] The peaks at 1566 and 1378 cm−1 are assigned to characteristic vibrations of the carboxyl group in thiolglycolic acid (TGA) [22] In Fig 3(c), FTIR spectrum of PVA-ZnS:Mn2+ QDs also shows characteristic peaks of PVA and TGA Moreover, the vibration of –OH group is shifted towards the shorter wavenumber at 3377 cm−1 The result indicates the bond between the –OH group of PVA molecules and ZnS:Mn2+ QDs The shift and increase of the vibrational bands’ intensity at 887 and 551 cm−1 were also observed in Fig 3(c) Additionally, the decrease of the C-O stretching peak intensity at 1090 cm−1 was observed in PVA-ZnS:Mn2+ QDs which is due to the decrease of the PVA crystallinity degree [10] The results indicate an interaction between ZnS:Mn2+ QDs and PVA molecules via the formation of OH-Zn2+ complexes Consequently, the XRD and FTIR results strongly support the formation of PVA-encapsulated ZnS:Mn2+ QDs (1) where D is the crystallite size, λ is the wavelength of X-ray (λ = 1.5406 Ǻ), θ is the Bragg angle and βhkl is the full-width at half maximum (FWHM) of the diffraction peak (in radians) at 2θ Based on the FWHM of (111) reflection, the crystallite sizes of ZnS:Mn2+ QDs and PVAZnS:Mn2+ QDs were estimated to be 2.2 nm and 2.5 nm, respectively The increase of the crystallite size is due to the formation of the PVA shell around the ZnS:Mn2+ QDs Fig shows the TEM images of ZnS:Mn2+ QDs, and PVA-ZnS:Mn2+ QDs, respectively The TEM images reveal that the ZnS:Mn2+ QDs are spherical in shape The particle sizes were estimated to be 7.5 and 10 nm for the ZnS:Mn2+ QDs and the PVA-ZnS:Mn2+ QDs, respectively The trend of the particle size increase is reasonable agreement with the XRD analysis However, the particle size is larger than the crystallite size, indicating that the particles probably are polycrystalline 3.2 FTIR spectra Fig shows the FTIR spectra of pure PVA, ZnS:Mn2+ QDs, and PVA-ZnS:Mn2+ QDs in the range of 400–4000 cm−1 In Fig 3(a), FTIR spectrum of the pure PVA sample clearly reveals the major peaks associated with poly(vinyl alcohol) For example, it can be observed the –OH stretching band at 3377 cm−1, the stretching C-H from the alkyl 3.3 Optical properties Fig shows the UV – vis spectra of the aqueous solution of PVA, ZnS:Mn2+ QDs aqueous solution, and PVA-ZnS:Mn2+ QDs aqueous solution, respectively The PVA solution showed the relatively weak peaks at 275 and 335 nm (Fig 4(a)) These peaks are attributed to the π-π* transition of C˭C bond and the n-π* transition of C˭O bond, respectively [14,23,24] Besides, the absorption peaks appeared at about 290 nm for the ZnS:Mn2+ QDs aqueous solution and at 294 nm for PVAZnS:Mn2+ QDs as Fig 4(b,c) The result shows that a slight red shift (≈ nm) has been observed with the PVA-ZnS:Mn2+ QDs indicating an increase in particle size The optical bandgap values at these absorption peaks were estimated to be Eg* = 4.27 and 4.22 eV for the ZnS:Mn2+ QDs and the PVA-ZnS:Mn2+ QDs, respectively All absorption peaks are significantly blue-shifted from the bulk ZnS (3.6 eV) indicating the quantum confinement effect [1] Additionally, the particle size (2R, diameter) of the QDs can be determined by [9]: d (2R) = 0.32 − 2.9 E − 3.49 3.5 − E (2) (Eg*) where E is the optical bandgap in eV and d(2R) is the average diameter of the QDs in nm The average diameters were calculated to be 2.9 and 3.0 nm for the Fig FT-IR spectra of (a) pure PVA, (b) ZnS:Mn2+ QDs and (c) PVAZnS:Mn2+ QDs 535 Journal of Luminescence 203 (2018) 533–539 T.P Nguyen et al However, for the PVA-ZnS:Mn2+ QDs, the peak position of the near edge absorption transition of the ZnS host was shifted towards the longer wavelength at 339 nm, which is due to increase in particle size The result is reasonable agreement with the UV-vis result Besides, the positions of the five excitation peaks of Mn2+ ions are not changed compared with those in bulk ZnS:Mn The result indicates that these ZnS:Mn2+ QDs have the similar degree of the sp-d mixing in comparison with the bulk material [26] Moreover, the energy of the Mn2+ emission band of ZnS:Mn2+ is a function of the crystal field strength Dq and the Racah parameter B [27] The B value depends strongly on the covalent interaction between 3d electrons of the Mn2+ ions and the surrounding ions and decreases from the Mn2+ free-ion value The Racah parameters for the free-ion are B = 860 cm−1 and C = 3850 cm−1 while those for the ZnS:Mn2+ bulk crystal are B = 609 cm−1, C = 3111 cm−1 and Dq = 667 cm−1 [26,27] The parameters B, C and Dq were determined by the following equations: Fig UV – vis absorption spectra of (a) PVA aqueous solution, (b) ZnS:Mn2+ QDs and (c) PVA-ZnS:Mn2+ QDs 10B + 5C = A1 , 4E ( 4G ) (3) 17B + 5C = 4E (4D) (4) 100Dq2 − (14B + 5C − E2)⋅(22B + 7C − E2) ZnS:Mn2+ QDs and the PVA-ZnS:Mn2+ QDs, respectively These particle sizes are smaller than the exciton Bohr diameter of ZnS (2αB~5 nm) [2] It is indicated that the strong quantum-size effect appears in all the samples Moreover, the particle sizes are larger than the crystallite sizes obtained from XRD pattern analysis The result is also consistent with the observations of Refs [1,9,25] It is due to the fact that the XRD analysis is only sensitive to the crystalline core size while the particle size from the UV-Vis spectroscopy can be affected by the solvent [24] The PLE measurement is a method to provide direct information on the energy level structure of the Mn2+ ions in ZnS:Mn2+ quantum dots Fig shows the PLE spectra of ZnS:Mn2+ QDs and PVA-ZnS:Mn2+ QDs at room temperature, respectively The PLE spectrum was measured by exciting the QDs and monitoring the characteristic orange-red emission of Mn2+ at 588 nm For the ZnS:Mn2+ QDs, the maximum excitation peak appeared at about 322 nm and the other smaller peaks in the range of 360–540 nm were observed in the inset of Fig According to the references [26–28], the peak excitation of 322 nm is related to the near edge absorption transition of the ZnS host whereas the smaller peaks at about 390, 430, 467, and 496 nm are attributed to the transitions between the 6A1(6S) ground state and the excited states of 4E(4D), 4T2(4D), A1(4G)-4E(4G), and 4T2(4G) within 3d5 configuration of the Mn2+ ions, respectively The excitation peaks of Mn2+ the d-d excitation transitions are relatively small since they are forbidden transitions [29,30] = 12B2 (E2 − 22B − 7C ) 13B + 5C − E2 (5) where E2 = E( T2) – E( A1) Based on the PLE spectra (the inset of Fig 5), the parameters B, C and Dq were calculated to be 600, 3082, and 587 cm−1, respectively The values of B and Dq are smaller compared to bulk ZnS:Mn2+, the results indicate that the covalent interaction between the Mn2+ ions and the surrounding S2- ions [26,27] Additionally, Chen et al.[27] reported that the change in crystal field strength is not the main reason for the emission shift of Mn2+ in ZnS:Mn2+ QDs Besides, the relative PLE intensity ratio (I467/IZnS) of 6A1(S) → 4A1, 4E(4G) direct excitation bands at 467 nm to the band-band transition at 322 and 339 nm increased from I467/IZnS = 0.016–0.053 for ZnS:Mn2+ QDs and PVAZnS:Mn2+ QDs, respectively The PLE enhancement can be attributed to sensitizers which predominantly absorbed the energy of exciting light and then transferred to the emitting Mn2+ centers [26,35] Fig shows the photoluminescence (PL) spectra of the PVA powder, the PVA aqueous solution, ZnS:Mn2+ QDs powder and PVAZnS:Mn2+ QDs powder under 325 nm excitation It is very interesting Fig PL spectra of (a) pure PVA powder, (b) PVA aqueous solution (4.5 × 10−5 M), (c) ZnS:Mn2+ QDs powder and (d) PVA-ZnS:Mn2+ QDs powder Fig PLE spectra of ZnS:Mn2+ QDs and PVA-ZnS:Mn2+ QDs monitored at 590 nm 536 Journal of Luminescence 203 (2018) 533–539 T.P Nguyen et al to see that the PVA powder is little emission under 325 nm excitation (Fig 6(a)) However, the PVA aqueous solution is strongly emissive with a peak maximum at 418 nm (Fig 6(b)) which attributes to n ← π* electronic transition in non-bonding 2p2(O) electrons in free OH groups in the syndiotactic configuration of PVA polymer molecules (s-PVA) [23,31] In the s-PVA configuration, the OH groups regularly alternate from one side of the plane to the other Moreover, Ram and co-workers [23] reported that a pure PVA had 43% syndiotactic-PVA, 38% atacticPVA and 19% isotactic-PVA For the ZnS:Mn2+ QDs powder (Fig 6(c)), the PL peak at about 400 nm (blue emission) is due to defect-states in the ZnS host [32,33] and the other peak at about 588 nm (orange-red emission) is assigned to the Mn2+ 4T1 – 6A1 emission [17,29] The blue emission (BE) peak at about 400 nm is attributed to the recombination of electrons in sulfur vacancy (VS) states with holes in the ground states of ZnS host [32,33] while the orange-red emission (OE) at 588 nm occurs due to spin forbidden 4T1(G) (excited) – 6A1(S) (ground) transition within 3d5 shell of Mn2+ via energy transfer from the ZnS host to the d electrons of Mn2+ ions [34–36] However, for PVA-ZnS:Mn2+ QDs powder, the BE peak was observed at 415 nm while the OE peak was observed at 600 nm as Fig 6(d) The very small red-shift (≈ 12 nm) compared with the core ZnS:Mn2+ QDs observed from the PVA-ZnS:Mn2+ QDs indicates that surface states of the ZnS:Mn2+ QDs were effectively passivated by PVA molecules [11] As a result, the PVA capping agent minimized the surface defects and enhanced the possibility of the energy transfer process from the ZnS host lattice to Mn2+ centers The red-shift phenomenon was also observed in the reports of Refs [14,27] Especially the PL intensity of Mn2+ 4T1 – 6A1 emission at 600 nm (Fig 6(d)) was significantly enhanced while the reduction of PL emission intensity at 415 nm was observed with the PVA encapsulated ZnS:Mn2+ QDs (PVAZnS:Mn2+ QDs) It is also in good agreement with the PLE analysis Thus, the studied result is suggested that the PL enhancement of the PVA-ZnS:Mn2+ QDs at 600 nm is due to the fact that (i) the surface states of the ZnS:Mn2+ QDs were effectively passivated by PVA molecules thus the excitation energy transfer from the ZnS host to the Mn2+ ions is more efficient and (ii) the efficient energy transfer process from the PVA capping agent to the Mn2+ luminescent centers Similarly, Fig shows the PL spectra of PVA aqueous solution (5.4 × 10−4 M), ZnS:Mn2+ QDs aqueous solution (1 g/l) and ZnS:Mn2+ QDs/PVA solution (1 g/l), respectively The studied result shows that the orange-red emission PL peak of ZnS:Mn2+ QDs aqueous solution was observed at about 588 nm and the blue emission was observed at Fig PL spectrum of PVA aqueous solution (a) and PLE spectrum of Mn2+ ions within ZnS:Mn2+ QDs The good overlap between the PVA (donor) emission and ZnS:Mn2+ QDs (acceptor) absorption is very evident Table FRET parameters of PVA-ZnS:Mn2+ QDs pairs Samples Overlap integral J, (M−1 cm3) Critical radius R0, (Ǻ) ФFRET, % PVA-ZnS:Mn2+ QDs 7.6 × 10−17 13 20.28 about 400 nm as Fig 7(b) However, for the ZnS:Mn2+ QDs dispersed in PVA (5.4 × 10−4 M) aqueous solution (ZnS:Mn2+ QDs/PVA), the orange-red emission PL intensity of the Mn2+ 4T1 – 6A1 transition at 615 nm was also enhanced while the PL intensity of PVA solution at 418 nm (Fig 7(a)) was significantly reduced and shifted to 430 nm as Fig 7(c) The strong red-shift of the orange-red emission PL peak (≈ 27 nm) compared with the core ZnS:Mn2+ QDs also observed from the ZnS:Mn2+ QDs/PVA solution indicates that surface states of the ZnS:Mn2+ QDs were passivated by PVA molecules [11,14,27] Moreover, the tail groups of PVA molecules anchored on the ZnS:Mn2+ particles surface with the increase of the PVA concentration, leading to the coarse surface [11] As a result, the non-radiation transfer processes are increased due to the surface states, so the PL efficiency of the Mn2+ T1 – 6A1 emission decreased From the analyzed results, we can suggest that PVA molecules interacted with the surface of ZnS:Mn2+ QDs and the energy transfer process from the PVA capping agent to the Mn2+ luminescent centers takes place under 325 nm excitation It is very probable that Mn2+ interstitial defects and Zn2+ ions at the surface interact with –OH hydroxyl groups of the PVA molecules via a kind of ligand reaction to form OH-Mn2+ and OH-Zn2+ complexes These complexes act as sensitizers (donor) which absorb the energy of exciting light and then is transferred to the luminescent Mn2+ ion centers (acceptor) Thus, the intensity of Mn2+ 4T1 – 6A1 emission is greatly enhanced for the PVAZnS:Mn2+ QDs Furthermore, Fig clearly shows the good overlap between the PVA emission and the Mn2+ ions absorption within ZnS:Mn2+ QDs It is a fundamental requirement to have resonance energy transfer (RET) from the donor to the acceptor [37] Consequently, when the ZnS:Mn2+ QDs are encapsulated by PVA molecules, the PVA can act as an energy donor while the Mn2+ ions within ZnS:Mn2+ QDs act as an acceptor The RET efficiency is usually determined through the Förster radius R0 given by the formula (6) [37]: Fig PL spectra of (a) PVA aqueous solution (5.4 × 10−4 M), (b) ZnS:Mn2+ QDs aqueous solution (1 g/l) and (c) ZnS:Mn2+ QDs/PVA solution (1 g/l) R0 = 537 9000 ln 10 k Φd ⋅J 128 π n4 NA (6) Journal of Luminescence 203 (2018) 533–539 T.P Nguyen et al Fig Schematic diagram of various electronic transitions and energy transfer process in poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots where k2 is an orientation factor in space of transition dipoles of donor and acceptor (k2 = 2/3), Фd is the quantum yield of the donor in the absence of acceptor (Фd = 0.34 [38]), n is the refractive index of the medium, NA is Avogadro’s number The refractive index (n) is typically assumed to be 1.33 for the PVA in aqueous solution J is the overlap integral between the donor emission band and the acceptor absorption band: that the efficient energy transfer takes place from the ZnS host and the PVA molecules to the Mn2+ centers under 325 nm excitation The energy transfer scheme of PVA-ZnS:Mn2+ QDs is also illustrated in Fig Conclusion The photoluminescence (PL) enhancement of the Mn2+ 4T1(G) – A1(S) emission intensity of PVA-ZnS:Mn2+ QDs is investigated in this study The studied results indicate that the PL enhancement at 600 nm is due to the fact that the PVA capping agent minimized the surface defects of ZnS:Mn2+ QDs and enhanced the possibility of the energy transfer process from the ZnS host lattice to Mn2+ centers Moreover, the photoexcitation energy transfer between PVA molecules and Mn2+ ions in ZnS:Mn2+ QDs is investigated in this study The similar result has been also observed in the ZnS:Mn2+/PVA solution It was found that interactions between ZnS:Mn2+ QDs and PVA molecules in PVAZnS:Mn2+ QDs and ZnS:Mn2+ QDs/PVA solution lead to Förster resonance energy transfer (FRET) efficiency from PVA molecules to the Mn2+ center within ZnS:Mn2+ QDs and the photoexcitation energy transfer efficiency is about 20.28% Our studied results are relevant to the application of hybrid organic/inorganic systems to light emitting devices J= ∫ IDH (λ) εA (λ) λ4 dλ (7) IDH (λ) is the normalized PL spectrum of energy donor where (∫ IDH (λ ) dλ = 1), εA(λ) is the molar extinction coefficient of the acceptor, λ is the wavelength The molar extinction coefficient of the ion Mn2+ at 525 nm is about εMn2+ ≈ 101 M−1 cm−1 [30] From Eqs (6) and (7), the efficiency of RET between the PVA donor and the Mn2+ acceptor (D – A) is given with: ΦET = R 06 + r6 R 06 (8) where R0 (Förster radius) is the D – A distance at which the transfer efficiency is 50%, and r is the D – A distance The active –OH groups of PVA molecules could interact with Zn2+ and Mn2+ ions of ZnS:Mn2+ QDs via a kind of ligand reaction to form OH-Zn2+ and OH-Mn2+ complexes Additionally, the ZnS:Mn2+ QDs radius is about 1.45 nm and the OH-Mn2+ bond length is about 1.83 Ǻ [39] Thus, the distance between D – A is considered as the sum of the ZnS:Mn2+ QDs radius and the OH-Mn2+ bond length As a result, the calculated values of overlap integrals, the critical radii of PVA-ZnS:Mn2+ QDs donor – acceptor pairs and the RET efficiency are listed in Table Moreover, Orlova and co-workers [40] reported that the efficiency of RET (ФRET) increased from 27% to 98% with the decrease of the distance between D – A from 5.5 nm to 1.75 nm Similarly, T Kezuka et al [41] have observed the energy transfer between poly(acrylic acid) (PAA) and Mn2+ ions in the composite film of nanocrystalline ZnS:Mn and PAA Later, K Manzoor et al [13] have also indicated that enhanced photoluminescence has been observed from the polyvinyl pyrrolidone (PVP) capped ZnS:Mn2+ nanoparticles due to efficient energy transfer from the surface adsorbed PVP molecules to Mn2+ luminescent centers in nanocrystals Recently, K Sabira and co-workers [42] have reported that the photoluminescence quantum yield of the poly(vinylidene fluoride)/ ZnS:Mn2+ (PVDF/ZnS:Mn2+) nanocomposite film was about 8.15% Therefore, from these analyzed results, we can conclude that the PL enhancement of the PVA encapsulated ZnS:Mn2+ QDs is due to the fact Acknowledgement This work was supported by the Center for Science and Technology Development (TST), the Printing Material Lab, Ho Chi Minh City University of Technology and Education and the Applied Physical Chemistry Lab, University of Science Ho Chi Minh City References [1] R.M Krsmanović Whiffena, D.J Jovanović, Ž Antić, B Bártová, D Milivojević, M.D 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