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|Title: ||自我還原 (Ca,Sr)S:Eu2+與微波均質Y2O3:Eu3+製備藍光激發之奈米級紅光螢光粉研究|
Investigations on self-reduced (Ca, Sr)S: Eu2 + and microwave homogenized Y2O3: Eu3 + nano-phosphors with red luminescence by broad-band blue-light excitation
|Authors: ||Chen-Yu Wu|
|Contributors: ||NTOU:Department of Marine Engineering|
|Keywords: ||自我還原，Y2O3: Eu3+，(Ca,Sr)S:Eu2+，藍光激發，紅色螢光體|
self-reduction, Y2O3: Eu3+, (Ca,Sr)S:Eu2+, blue-light excitation, red phosphors
|Issue Date: ||2013-10-07T03:01:19Z
|Abstract: ||使用藍光激發等向性佳的紅光奈米螢光粉，可提高白光LED或顯示器之色彩飽和度與發光強度。本研究利用濕式化學製程製作螢光粉，掌控其維度之等向性與尺度。在Y2O3:7mol% Eu3+製備中，利用尿素水解製作出分子形貌等向性佳的前驅物(YCO)球型粒子，並利用成核成長的過程掌控尿素水解法的前驅物粒徑成長的大小。傳統尿素水解反應時間太長，本研究加入低瓦數的微波100W-3.5min進行尿素溶劑/水解製程，以低界面能乙二醇為溶劑，製作出奈米級(25nm)之Y2O3: 7mol% Eu3+前驅物。利用微波溶劑解製作出的奈米級前驅物經過800℃熱處理後，其形貌仍維持奈米級，經466nm激發，所得紅光611nm強度已不亞於商業級粉末。 尿素水解陽離子的前驅物含有大量羰基，所以可以維持等向性佳的球型，其代價為熱處理溫度高達700~800℃方可將其羰基轉變成二氧化碳，此過程除了耗能且會增加粉末間頸縮成長的問題。本研究進一步利用KOH強鹼加入微波尿素溶劑解製程中(pH=9.5)，減少羰基反應，並且維持等向性佳的球形粒子，此種前驅物經過600℃熱處理後仍維持奈米尺度，並且具有466nm激發的良好紅光強度。 Eu3+藍光激發只限定於466nm，在許多藍光背光源是無法有效的運用。因此，本研究開發寬藍光激發範圍(380~550nm)均可激發的(Ca,Sr)S:Eu2+紅光(600~700nm)螢光粉。利用高溫迴流法異質成核前驅物在奈米碳球上(核殼法)，將其置於氮氣氛中，800℃熱處理，藉碳球燃燒產生一氧化碳，消除前驅物殘存的氧，同時還原Eu3+成為Eu2+，是一種自發性還原反應。此種還原過程具有一氧化碳保護氣氛，除了可以不需加入氫氣，也不需加入硫等有毒氣體做為補償氣氛，即可完成主體晶格成相與發光中心的價數調整。此種熱處理製程後之CaS:Eu2+螢光體仍維持40nm的尺度，其PL發光強度比起傳統固態法合成之大晶粒螢光體來的強。 本研究成功利用異質與均質成核的濕式化學製程控制藍光激發之紅光螢光粉尺度與等向性，進一步開發環保、簡化與低溫的自我還原製程，提升藍光激發的紅色螢光體發光強度。|
The color saturation and luminous intensity of white light LEDs or displays can be improved by use of isotropic red nano-phosphors which are excited by blue-light. This thesis uses wet chemical method to prepare and control phosphors’ particle size and isotropic dimension. The Y2O3 : 7mol% Eu3+ phosphors were prepared by urea hydrolysis to form isotropic molecular precursor (YCO) which grew into spherical particles. The particles growth mechanism in different solvents such as ethylene glycol or water was a zero-order chemical reaction. The growth of precursor particle size could be controlled by the zero-order chemical reaction process. Generally, the traditional urea hydrolysis reaction proceeds for a long time. When the low power microwave energy was utilized to drive the urea hydrolysis or solvolysis (100W-3.5 min) in a low surface energy solvent of ethylene glycol, the Y2O3 : 7mol% Eu3+ precursors were formed with nano-particle size of 25 nm. Such microwave-prepared precursors continued to maintain nano-particle size after 800C calcination and emitted 611 nm red-light under the 466 nm excitation. The urea-hydrolyzed precursors contained a lot of carbonyl groups (C=O) to maintain the isotropically spherical particles. It needed high calcined temperatures of 700-800C to remove the carbonyl groups. Energy consumption and particles necking occurred during the heat treatment. A strong base of KOH was added into microwave-driven urea solvolysis (pH=9.5) to reduce the amount of carbonyl groups in reaction and maintained the isotropically spherical particles. This process only required post-heat treatment at 600C as to maintaining the isoptropic and nano-size of particles. The red-light was well emitted by 466 nm excitation. The red-light emission of Eu3+ was restricted under the excitation of narrow band of 466 nm. It is expected that the luminescence can be generated from the broad-band back-light. This work also investigates the (Ca,Sr)S : Eu2+ with the 600~700 nm red-light emission under the excitation of broad-band blue-light of 380~550 nm. A novel core-shell technique was developed to heterogeneously nucleated CaS : Eu2+ and (Ca,Sr)S : Eu2+ precursors on pseudo-nano-carbon balls surface by reflux process. The CaS : Eu2+ and (Ca,Sr)S : Eu2+ nano-phosphors were then formed by self-reduction of Eu3+ to Eu2+ in a nitrogen atmosphere at 800C and then emit strong 600~700 nm red-light by 380~550 nm irradiation. The carbon balls core self-oxidized the residual oxygen to produce a reduction atmosphere without extra additions of hydrogen and poisonous sulfur to compensate sulfur atmosphere for the (Ca,Sr)S phosphors. Such core-shell template technique may accomplish host phases crystallization and valence adjustment of activators in one process simultaneously. The CaS : Eu2+ nano-phosphors of 40 nm were achieved with the self-reduction technique. Such photoluminescent intensity (PL) is higher than the large grained phosphors from conventional mixed oxide preparation. This thesis utilized homogeneous and heterogeneous nucleation processes to prepare and control the isotopic and nano-sized characteristics of blue-light excited red phosphors. Furthermore, the PL enhancement under blue-light excitation is completed by developing environmental friendliness, simple and low temperature self-reduction process.
|Appears in Collections:||[輪機工程學系] 博碩士論文|
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