Tổng hợp vật liệu huỳnh quang ba màu sử dụng trong các đèn huỳnh quang compact

Tổng hợp vật liệu huỳnh quang ba màu sử dụng trong các đèn huỳnh quang compact Tổng hợp vật liệu huỳnh quang ba màu sử dụng trong các đèn huỳnh quang compact Tổng hợp vật liệu huỳnh quang ba màu sử dụng trong các đèn huỳnh quang compact luận văn tốt nghiệp,luận văn thạc sĩ, luận văn cao học, luận văn đại học, luận án tiến sĩ, đồ án tốt nghiệp luận văn tốt nghiệp,luận văn thạc sĩ, luận văn cao học, luận văn đại học, luận án tiến sĩ, đồ án tốt nghiệp

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF TECHNOLOGY INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE BUI VAN HAO SYNTHESIS OF TRICOLOR PHOSPHORS USED IN FLUORESCENT AND COMPACT FLUORESCENT LAMPS MASTER THESIS OF MATERIALS SCIENCE BATCH ITIMS - 2006 Supervisor: Assoc Prof Dr Pham Thanh Huy Hanoi - 2008 BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU BÙI VĂN HÀO TỔNG HỢP VẬT LIỆU HUỲNH QUANG BA MÀU SỬ DỤNG TRONG CÁC ĐÈN HUỲNH QUANG VÀ HUỲNH QUANG COMPACT LUẬN VĂN THẠC SĨ KHOA HỌC VẬT LIỆU KHOÁ ITIMS - 2006 Người hướng dẫn: PGS TS Phạm Thành Huy Hà Nội - 2008 Acknowledgments Firstly, I am deeply thankful my supervisor, Assoc Prof Dr Pham Thanh Huy for his direct guidance and financial support during my study He has believed and created the best conditions for my research I would like to thank and give my best regards to the directorate and all the teachers, scientists of ITIMS who have brought me much knowledge through interesting lessons and opportunities in future I further thank to Dr Tran Ngoc Khiem, Dr Trinh Xuan Anh, Dr Le Anh Tuan, MSc Tran Trong An, MSc Phi Van Luong, Nguyen Manh Cuong, Duong Thanh Tung and other members of Photonics and Optoelectronics Lab for their kind help during my research I would also like to thank to the directors of Quy Nhon University for the permission and financial support for my study Finally, I am deeply thankful my family and all my friends who have helped, encouraged and supported me at any time Hanoi, September 2008 Master student: Bui Van Hao Contents Introduction Chapter 1: An overview of phosphors used in lighting devices 1.1 Early phosphors for fluorescent lamps 1.2 Tricolor phosphors for luminescent lamps based on rare earth activators 1.2.1 Blue emitting phosphors 1.2.2 Green emitting phosphors 11 1.2.3 Red emitting phosphors 12 1.3 Phosphor synthesis methods 13 1.3.1 Solid state reaction method 13 1.3.2 Combustion synthesis 13 1.3.3 Spray pyrolysis 13 1.3.4 Sol-gel method 15 Chapter 2: Experimental 18 2.1 Preparation of blue-emitting phosphor BaMgAl10O17:Eu2+ by sol – gel method 18 2.2 Preparation of green emitting phosphors (LaGd)PO4:Tb3+ by sol – gel method 20 2.3 Preparation of red emitting phosphors Y2O3:Eu3+ by sol – gel method 21 2.4 Material characterization and analysis 23 2.4.1 Infrared spectroscopy 23 2.4.2 X-ray diffraction techniques 26 2.4.3 Scanning electron microscopy (SEM) 29 2.4.4 Transmission electron microscopy (TEM) 32 2.4.5 Photoluminescence spectroscopy - Luminescence and excitation spectra 33 Chapter 3: Results and discussion 35 3.1 Structure and luminescent properties of BaMgAl10O17:Eu2+ blue emitting phosphor 35 3.1.1 Crystalline structure of the powders 35 3.1.2 Morphology of the phosphor 39 3.1.3 Photoluminescent spectra of the phosphors 40 3.2 Structure and photoluminescent properties of (LaGd)PO4:Tb3+ green emitting phosphor 46 3.2.1 Crystalline structure of the phosphor 46 3.2.2 Morphology of the phosphor 48 3.2.3 Photoluminescent properties of the phosphors 49 3.3 Structure and photoluminescent properties of Y2O3:Eu3+ red emitting phosphor 52 3.3.1 Formation of Y2O3:Eu3+ phosphor using citric acid as chelating agent in the sintering process 52 3.3.2 Morphology of Y2O3:Eu3+ phosphor 54 3.3.3 Luminescent properties of the phosphors 55 3.3.4 Effect of the ratio of metal ions to acid on particle size and luminescent properties of the phosphors 63 Conclusions 65 -1- INTRODUCTION In modern society, people rely heavily on rare earth based devices In almost any office, light is produced by fluorescent lamps in which UV radiation from mercury plasma is converted into visible light by rare-earth based phosphors In addition, in our information society, vast amounts of information are read from displays, in most cases CRTs, in which rare-earth materials are applied After more than 50 years of extensive research on the luminescent materials applied in lamps and displays, compounds are obtained with almost ideal physical properties: very high energy efficiencies for cathoderay phosphors and very high UV absorptions and quantum efficiencies for lamp phosphors In fluorescent lamps with a very high color rendering index (CRI), three or more phosphors are applied In Philips high-quality fluorescent lamps with the so-called 'Color 80' phosphor blend, BaMgAl10O17:Eu (BAM), (Ce,Gd,Tb)MgB5O10 (CBT) and Y2O3:Eu (YOX) are used as blue-, greenand red-emitting phosphors, respectively In these materials, rare-earth ions are applied for absorption of the UV radiation and the generation of visible light Bui Van Hao - ITIMS 2006 -2- The phosphor price contributes considerably to the price of the lamp (tens of percent) Therefore, cost price reduction is a very important topic in research on phosphors to be applied in fluorescent lamps An obvious way to reduce the cost price of the phosphors is to optimize the preparation of the phosphors or to reduce the amount of phosphor applied in the lamp, e.g by reducing the grain size of the phosphors In this thesis, synthesis processes and luminescent properties of tricolor phosphors are presented The phosphors we aim to prepare are BaMgAl10O17:Eu2+, (La,Gd)PO4:Tb3+ and Y2O3:Eu3+ corresponding to blue-, green- and red-emitting phosphors, respectively Sol – gel is chosen as the method to synthesize the phosphors Bui Van Hao - ITIMS 2006 INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE (ITIMS) BATCH ITIMS – 2006 Title of Master Thesis: “SYNTHESIS OF TRICOLOR PHOSPHORS USED IN FLUORESCENT AND COMPACT FLUORESCENT LAMPS” Author: Bui Van Hao Supervisor: Assoc Prof Dr Pham Thanh Huy Referees: Abstract: In this thesis, structure and luminescent properties of tricolor phosphors prepared by sol–gel method are presented We aim to synthesize BaMgAl10O17:Eu2+, (La,Gd)PO4:Tb3+ and Y2O3:Eu3+ as blue-, green- and redemiting phosphors, respectively The starting materials contain rare-earth oxides, metal nitrates and metal phosphates To dissolve oxides into solution, nitric acid is used Citric acid and tartaric acid are employed as chelating agents in making sol Several factors effecting on structure and luminescent properties of the phosphors such as doping concentration, sintering temperature are examined Crystalline structure of the powder is investigated by X-ray diffraction (XRD) technique Morphology and particle size of the phosphors are observed by scanning electron microscope (SEM) and transmission electron microscope (TEM) Photoluminescence measurements are performed using a continuous wave He–Cd laser (325 nm) as the excitation source VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU KHÓA ITIMS – 2006 Tên luận văn: “TỔNG HỢP BỘT HUỲNH QUANG BA MÀU SỬ DỤNG TRONG CÁC ĐÈN HUỲNH QUANG VÀ HUỲNH QUANG COMPACT” Tác giả: Bùi Văn Hào Người hướng dẫn: PGS TS Phạm Thành Huy Người nhận xét: Tóm tắt: Trong luận văn chúng tơi trình bày cấu trúc tính chất phát quang bột huỳnh quang ba màu tổng hợp phương pháp sol-gel Mục đích chúng tơi chế tạo bột BaMgAl10O17:Eu2+, (La,Gd)PO4:Tb3+ Y2O3:Eu3+ tương ứng với màu phát quang xanh lam, xanh lục đỏ Các vật liệu ban đầu bao gồm ơxít đất muối kim loại Axít nitric dùng để hồ tan ơxít thành dung dịch muối Axít citric axít tactaric dùng làm tác nhân tạo sol Một số yếu tố ảnh hưởng đến cấu trúc tính chất phát quang bột phát quang nồng độ pha tạp, nhiệt độ thiêu kết khảo sát Cấu trúc tinh bột nhận được khảo sát nhờ kỹ thuật nhiễu xạ tia X Hình thái kích thước hạt quan sát công nghệ hiển vi điện tử quét (SEM) hiển vi điện tử truyền qua (TEM) Các phép đo phổ huỳnh quang bột phát quang thực với nguồn kích thích laser He-Cd bước sóng 325 nm -3- Chapter AN OVERVIEW OF PHOSPHORS USED IN LIGHTING DEVICES 1.1 Early phosphors for fluorescent lamps A fluorescent lamp is filled with a noble gas at a pressure of 400 Pa, containing 0.8 Pa mercury Under the excitation of electrons accelerated by electric field inside the tube, mercury atoms are excited In the process of returning to the ground state, they emit radiations which are mainly in ultraviolet region About 85% of emitted radiation is at 254 nm and 12% at 185 nm The rest 3% is at longer wavelength ultraviolet and visible region (297, 302, 313, 334, 365, 405, 408, 436, 546, 576 and 579 nm) The lamp phosphors should convert 254 and 185 nm radiations into visible light The luminescent activators of the phosphors absorb these radiations and emit other wavelengths in visible region when they return to ground state Requirements for the practical use of phosphors in fluorescent lamps are high emission efficacy under excitation with 254 nm radiation and physical and chemical stability in the rare gas/mercury discharge space In the early time of luminescent lighting (1938-1948), a mixture of two phosphors was used, namely MgWO4 and (ZnBe)2SiO4:Mn2+ While the former has a broad bluish-white emission band with a maximum at 480 nm (figure 1.1) and can be efficiently excited by short wavelength ultraviolet region, the latter gives an emission spectrum that covers the green to red part of visible spectrum (figure 1.2) Bui Van Hao - ITIMS 2006 - 52 - 3.3 Structure and photoluminescent properties of Y2O3:Eu3+ red emitting phosphor 3.3.1 Formation of Y2O3:Eu3+ phosphor using citric acid as chelating agent in the sintering process Fig 3.12 IR spectra of the phosphors before sintering and sintered at different temperatures Figure 3.12 shows the IR spectra of Y2O3:Eu3+ phosphors before sintering and sintered at different temperatures For the dry gel before calcination, the IR spectrum consists mainly of three parts: the first part with a peak at 3438.5 cm-1 arises from the absorption of O–H vibration; the second part with the main peaks at 1418.3 and 1541.2 cm-1 comes from citrate groups Bui Van Hao - ITIMS 2006 - 53 - and the third part with a weak peak at 845.3 cm-1 due to the absorption of small amount of CO32– After sintering at 600 oC, the absorption peaks from the organic components decrease, and a new sharp peak at 560 arises due to the absorption of Y2O3 The absorption of organic composition almost disappeared after sintering at 900 oC and only the absorption of Y2O3 is considerable XRD patterns of phosphors sintered at different temperatures are shown in figure 3.13 The powder crystallized completely at the temperature of 600 o C The set of peaks obtained correspond to characteristic peaks of Y2O3 cubic phase So we can conclude that our powders have cubic crystalline structure Narrow peaks indicate large particle size of the phosphors Fig 3.13 XRD patterns of the phosphors sintered at different temperatures Bui Van Hao - ITIMS 2006 - 54 - 3.3.2 Morphology of Y2O3:Eu3+ phosphor Fig.3.14 SEM image of the powder sintered at 900 oC for hours Bui Van Hao - ITIMS 2006 - 55 - Figure 3.14 shows SEM image of the powder sintered at 900 oC in hours It can be seen that nearly spherical particles are obtained and particle size is estimated from to µm 3.3.3 Luminescent properties of the phosphors Emission spectrum of the phosphor with europium atom concentration of 7% sintered at 900 oC for hours when excited by 325 nm beam are shown in figure 3.15 It can be seen that the phosphor has an intensive fluorescence with a sharp peak at the wavelength of 611.5 nm corresponding to the transition between 5D0 and 7F2 energy levels of Eu3+ ions Fig 3.15 Emission spectrum of the phosphor sintered at 900 oC for hours, λex = 325 nm Bui Van Hao - ITIMS 2006 - 56 - The emission intensity of the phosphors depends on the Eu3+ concentration and sintering temperature As shown in figure 3.16, the strongest emission intensity corresponds to the concentration of at.% Higher concentrations cause the decrease of emission intensity This effect may be attributed to the concentration quenching mechanism [15] Fig 3.16 Concentration dependence of emission intensity of the phosphors Effect of sintering temperature on photoluminescent intensity was investigated The emission intensity increases with the increase of temperature The optimal sintering temperature to obtain the highest is 900 o C Higher sintering temperatures cause the decrease of emission intensity This can be explained that at higher temperatures, particles tend to move into clusters, as a result, the emission intensity will be decreased Bui Van Hao - ITIMS 2006 - 57 - Fig 3.17 Sintering temperature dependence of emission intensity of the phosphors Similar results have been obtained in case of using tartaric acid as chelating agent We have used tartaric acid for the purpose of nanoscaled phosphor synthesis Fig 3.18 XRD patterns of the powders sintered at different temperatures Bui Van Hao - ITIMS 2006 - 58 - X-Ray diffraction patterns of nanophosphors are shown in figure 3.18 Like the microphosphors, the nanoscaled phosphors have cubic structure In figure 3.19 are FE-SEM and TEM images of the nanoparticles obtained by sintering the dry gel at 800 oC for hours From these images we can see that the particles are rather homogeneous and the grain size is evaluated in the range of 20 to 30 nm Crystallite size of the nanophosphors can be calculated according to Scherrer formula [16]: D = 0.89λ , where D is β cos θ the crystallite size diameter (nm), λ is the X-ray wavelength (0.15405 nm), θ is the diffraction angle and β is the full-width at half-maximum (FWHM, in radian) of (222) peak The results are summarized in the table 3.1 These results are in good agreement with the particle size observed by FE-SEM and TEM Bui Van Hao - ITIMS 2006 - 59 - Fig 3.19 FE-SEM and TEM images of the nanophosphors Bui Van Hao - ITIMS 2006 - 60 - Table Crystallite size of the phosphors Sample Sintering temperature Peak position FWHM D (nm) 600 oC 29.03o 0.883o 700 oC 29.12o 0.543o 15 800 oC 29.12o 0.505o 16 900 oC 29.15o 0.410o 20 Emission spectrum of the nanophosphor is shown in figure 3.20 Photoluminescence measurements were performed using a continuous wave He–Cd laser (325 nm) as the excitation source Fig 3.20 Photoluminescent spectrum of the nanophosphor Bui Van Hao - ITIMS 2006 - 61 - Let’s take a comparison between emission spectra of micro and nanophosphors No significant difference in position of the peaks between two spectra, but there is a little difference in shape of the curves The emission bandwidth of the nanophosphors is larger than that of the microphosphors The increasing bandwidth results from the increase of the lattice relaxation energy of the excited state with decreasing particle size [17] Fig 3.21 A comparison between emission spectra of two kinds of phosphors The dependence of emission intensity on europium concentration and sintering temperature of the nanophosphors (figure 3.22) is similar to that of the microphosphors The optimum europium concentration is at.% and temperature is 800 oC Bui Van Hao - ITIMS 2006 - 62 - (a) (b) Fig 3.22 Dependence of emission intensity on Europium concentration (a) and sintering temperature (b) Bui Van Hao - ITIMS 2006 - 63 - A general comparison of emission intensities of two kinds of phosphors can be inferred The results show that the microphosphors have stronger emission intensity than that of the nanoparticles in the same conditions of concentration and temperature Nanoscaled phosphors have lower quantum efficiency compared to microscale particles This is attributed to the large surface area, which amplifies quenching processes [18] Fig.3.23 Emission intensity of Y2O3:Eu3+ as a function of sintering temperature 3.3.4 Effect of the ratio of metal ions to acid on particle size and luminescent properties of the phosphors In this work, different molar ratios of metal ions to citric acid and tartaric acid (1:1, 1:2, 1:3, and 1:4) were studied At the ratio of 1:1, the particles Bui Van Hao - ITIMS 2006 - 64 - were in an inhomogeneous form Other ratios did not make an obvious change in particle size Fig 3.24 Dependence of emission intensity on metal ion : acid molar ratio When the ratio of metal ion to acid was 1:2, the highest emission intensity was obtained This can be explained that high acid concentration causes a higher carbon impurity left in the powder which decreases luminescent intensity while the lower acid amount accelerates the rate of hydrolysis in solgel process, as a result, the nanoparticles could not be homogeneous [19] Bui Van Hao - ITIMS 2006 - 65 - CONCLUSIONS In general, we have been successful in preparing tricolor phosphors by sol – gel process The results can be briefly summarized as following: • For the blue emitting phosphors BaMgAl10O17:Eu2+: o BaMgAl10O17:Eu2+ hexagonal phase we aim to synthesize forms when sintered at 1200 oC o The particle size is in the range of 100 nm to 600 nm o Luminescent characteristics of BaMgAl10O17:Eu2+ appear for the samples sintered at 1300 oC and reduced at above 900 oC Emission intensity increases with the increase of reducing temperature • For the green emitting phosphors (La, Gd)PO4:Tb3+: o (La, Gd)PO4:Tb3+ crystalline phase forms at 700 oC with a variety of structures: hexagonal, tetragonal and monoclinic o The particle size varies from 100 nm to 700 nm o The optimum sintering temperature to obtain highest emission intensity is 800 oC • For the red emitting phosphors Y2O3:Eu3+: o The samples completely crystallized at 600 o C and the phosphors have cubic crystalline structure Bui Van Hao - ITIMS 2006 - 66 - o The grain size of the phosphors is in the range of – µm (the microphosphors - citric acid is used as chelating agent) and 20 – 30 nm (the nanophosphors - tartaric acid is used as chelating agent) o The optimum sintering temperature to obtain highest emission intensity is 900 o C (microphosphors) and 800 o C (nanophosphors) o The optimum europium doping concentration is at.% o The optimum ratio of metal ion to acid (chelating agent) is 1:2 Bui Van Hao - ITIMS 2006 ... TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU BÙI VĂN HÀO TỔNG HỢP VẬT LIỆU HUỲNH QUANG BA MÀU SỬ DỤNG TRONG CÁC ĐÈN HUỲNH QUANG VÀ HUỲNH QUANG COMPACT LUẬN VĂN THẠC SĨ KHOA HỌC VẬT LIỆU KHOÁ ITIMS - 2006... VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU KHÓA ITIMS – 2006 Tên luận văn: “TỔNG HỢP BỘT HUỲNH QUANG BA MÀU SỬ DỤNG TRONG CÁC ĐÈN HUỲNH QUANG VÀ HUỲNH QUANG COMPACT? ?? Tác giả: Bùi Văn Hào Người... Huy Người nhận xét: Tóm tắt: Trong luận văn chúng tơi trình bày cấu trúc tính chất phát quang bột huỳnh quang ba màu tổng hợp phương pháp sol-gel Mục đích chế tạo bột BaMgAl10O17:Eu2+, (La,Gd)PO4:Tb3+