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Investigations on Growth and Luminescent Persistence of Sulfide and Oxide Nano-Phosphors
|Authors: ||Wu, Chen-Yu|
|Contributors: ||NTOU:Department of Marine Engineering|
microwave-assisted process;in-situ reduction;inherited hydrothermal;Y2O3:Eu3+;(Ca,Sr)S:Eu2+;SrAl2O4:Eu2+,Dy3+
|Issue Date: ||2020-07-02T08:21:04Z
|Abstract: ||本研究成功利用微波輔助修飾與製備奈米氧化物螢光粒子，並且利用碳球模板還原法合成硫化物與氧化物奈米螢光粒子。進一步發展衍生性水熱法製備單晶板狀的奈米多元氧化物長時效性螢光粒子。 首先研究固態粉碎法將微米級Y2O3:Eu3+商用螢光粒子細化，發現破碎螢光粒子為奈米針刺狀粒子，利用微波能量可迅速修飾顆粒表面缺陷與晶體內部空缺。微波修飾後之螢光粒子仍維持奈米尺度與表面光滑的幾何結構，並保持與固態粉碎前相當的光學性質，成功利用微波修飾奈米化的商用Y2O3:Eu3+螢光粒子。 一般尿素水解合成前驅物過程既耗時又耗能，利用微波輔助液態尿素沉澱法增進化學反應，製備Y2O3:Eu3+奈米螢光粒子，既可縮短反應時間又可以節省能源損耗。進一步使用尿素水解法的溶劑為乙二醇，可以改變溶液界面能以控制Y2O3:Eu3+前驅物維持在奈米尺度下。再加入一些強鹼能控制製作時間，降低熱處理溫度至600C。使用微波液態輔助合成過程，成功地降低了前驅物合成時間與熱熱處理溫度，並且還可以維持在30-50nm良好結晶的Y2O3:Eu3+粒子形貌與特性。 Eu3+的f-f能態跳躍頻寬太窄不利於許多光譜上的運用，而Ce3+與Eu2+的5d14fn-14fn轉換可以控制光譜在不同的主體晶格場，但是還原激活劑的過程，傳統製程有許多高溫與氣氛的困難；本研究利用碳球為模板的核/殼結構，即碳球(核)/無機(硫,氧)化物前驅物(殼)，做為製備各種(Ca,Sr)S:Eu2+, CaS:Ce3+, SrY2S4:Eu2+, SrAl2O4:Eu2+等螢光體的前驅物，當碳球核燃燒時產生一氧化碳，消除前驅物殘存的氧，同時還原Eu3+成為Eu2+或Ce4+成為Ce3+，是一種自發同步還原反應。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，甚至對鹼土金屬硫化物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(Ca,Sr)S:Eu2+, CaS:Ce3+, SrY2S4:Eu2+, SrAl2O4:Eu2+等螢光體仍維持40nm的尺度，其光致發光(PL)強度比起傳統固態法合成之大晶粒螢光體來的強。另外，白光YAG之LED可以通過覆蓋本法製備之奈米CaS:Eu2+螢光粒子將演色指數(CRI)提高到96.77。 本研究利用衍生性水熱法製備長發光時效的綠光SrAl2O4:Eu2+,Dy3+螢光粒子，以NaAlO2做為鋁來源與礦化劑，無需額外添加強鹼當礦化劑。在水熱前/後加入少量硼酸鹽助熔劑來探討螢光增進效果；熱處理溫度1100C，成功獲得與維持單晶次微米/奈米厚度的板狀螢光粒子。因為單晶板狀奈米螢光粒子具有較高的表面積與較低光散射，其PL發光強度比一般多晶不規則形的螢光粒子高。研究結果指出硼酸鹽提供B3+的摻雜可以增進夜光時效性；水熱所得前驅物混合助熔劑可以形成SrAl2O4:Eu,Dy/B2O3的類核/殼結構；此構造可以提供抗環境性以保護奈米級板狀螢光粒子。|
In this study, microwave-assisted process has successfully modified and prepared nano-oxide phosphor particles. The carbon sphere templated core-shell reduction method is also successful in preparation of nano-oxide and sulfide phosphors. Finally, the inherited hydrothermal method proves successful synthsis of single-crystal nano-plate like long lasting phosphor particles. The nano-phosphor Y2O3:Eu3+ particles has needle-like surface made by sand milling from commercial micro particles. The microwave energy was used to modify the phosphor surfaces, and to remove the surface defects of phosphor particles. The smoothed Y2O3:Eu3+ particles can still maintain nano scale after microwave surface modification. Moreover, the nano smooth Y2O3:Eu3+ particles have almost the same photoluminescent property as commercial micro particles. The commercial Y2O3:Eu3+ particles size reduction and surface modification has been successfully done by microwave energy. The traditional urea hydrolysis method needs long aging time and wastes energy for the Y2O3:Eu3+ preparation. In this research, the microwave was used in hydrolysis process to promote reaction efficiency and reduce energy loss. Furthermore, the solvent in hydrolysis process can be replaced by ethylene glycol for reducing the interfacial energy between solvent and nuclei as to controlling the Y2O3:Eu3+ precursor particle size at nano scale. Such an organic solvent can reduce the heat-treating temperature to 600C by adding strong base to the urea hydrolysis solution. Therefore, the microwave assisted process successfully obtained well-crystallized Y2O3:Eu3+ 30-50 nm nano-particles and reduced the heat-treating temperature. The Eu3+ f-f state is a narrow band as to adjusting the spectra of electron transition necessarily for optical application. The spectra of Ce3+ and Eu2+ for 5d14fn-14fn transition are dependent on different crystal field around them. However, the reduction of activator is not easily controlled at high temperature and atmosphere limitation. A novel core-shell template technique was developed to heterogeneous nucleation and growth of (Ca,Sr)S:Eu2+ CaS:Ce3+、SrY2S4:Eu2+ and SrAl2O4:Eu2+ precursors on pseudo-nano-carbon sphere surface by a chemical reflux process. The nano-phosphors were formed by in-situ reduction of Eu3+-Eu2+/Ce4+-Ce3+ in a nitrogen atmosphere at 800C. The carbon spheres core self-oxidized the residual oxygen to produce a carbon monoxide reduction atmosphere preventing addition from hydrogen and poisonous sulfur to compensate sulfur atmosphere for the (Ca,Sr)S、SrY2S4 phosphors. Such a core-shell template technique may accomplish host phases crystallization and valence adjustment of activators in one process simultaneously. The (Ca,Sr)S:Eu2+, CaS:Ce3+, SrY2S4:Eu2+, SrAl2O4:Eu2+ nano-phosphors of 40 nm were achieved with the in-situ reduction technique. The photoluminescent (PL) intensities of such in-situ reduced nano-phosphors are higher than the large grained phosphors from conventional mixed oxide preparation. On the other hand, the YAG LED color rendering index (CRI) is modified to 96.77 by such an as-prepared CaS:Eu2+ nano phosphor addition. The long afterglow phosphors SrAl2O4:Eu2+,Dy3+ is prepared by inherited hydrothermal in this research. Such a process used the NaAlO2 as the aluminum source that can also play as the mineralizer role in the inherited hydrothermal process. The small amount of borate flux was added before and after the inherited hydrothermal process for the investigations on the optical properties of phosphors. The heat treatment temperature of 1100C for hydrothermal-prepared samples obtains nano-thick plate-like phosphor particles with single crystal. The plate-shaped nano particle of single crystal has a high surface area and low light-scattering so as to providing the photoluminescence (PL) property better than the irregular shaped particle of general polycrystal. In addition, the dopant of B3+ can enhance the long afterglow. On the other hand, a core/shell-like structure of SrAl2O4:Eu, Dy/B2O3 formed after the B2O3 addition to the as-prepared hydrothermal precursor of SrAl2O4:Eu, Dy. This core-shell-like structure can protect the nano-thick particle from harmfully environmental impact.
|Appears in Collections:||[輪機工程學系] 博碩士論文|
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