新穎矽氧化物與矽氮化物螢光材料之製備、結構解析與發光特性

Synthesis, Structural Characterization and Luminescence Properties of New Silicate and Nitridosilicate Phosphors

楊哲遠(Che-Yuan Yang)

指導教授 ： 呂宗昕

國立臺灣大學/工學院/化學工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201701126

摘要

為解決現有白光發光二極體(白光LED)色溫高及演色性差之缺點，本研究針對其中之螢光材料進行改良，製備出一系列新型矽氧化物與矽氮化物螢光材料。研究中透過發光中心間之能量轉移調控螢光粉體之激發與放光光譜；利用新型製程改善粉體之結晶性、粒徑分布以及發光效率；並透過粉體與藍光發LED晶片之實際封裝，製備出具備高演色性之白光LED。
論文中首先於第三章製備ZnGd4Si3O13: Tb3+, Mn2+新型矽氧化物螢光粉體。在紫外光的激發下，ZnGd4Si3O13: Mn2+呈現一寬廣之紅光放射峰，ZnGd4Si3O13: Tb3+則在波長490, 544, 585和621nm的位置產生數個狹窄的放射峰。透過將Tb3+摻雜於ZnGd4Si3O13: Mn2+中可利用Tb3+→Mn2+的偶極-偶極能量轉移機制對其放光強度造成100%的提升。另一方面，將Mn2+摻雜於ZnGd4Si3O13: Tb3+時則因能量轉移導致Tb3+之放光強度隨Mn2+之摻雜濃度下降。此外在電子束之激發下，ZnGd4Si3O13: Tb3+, Mn2+亦呈現顯著之放光現象，顯示其應用於陰極發光的潛力。
為了調整螢光粉體之有效激發波段，論文第四章選用Sr2Si5N8材料作為主體，利用鋱離子作為活化中心，透過反應溫度之調整控制粉體之放光特性。於較低溫度下合成之Sr2-xTbxSi5N8粉體呈現標準之Tb3+窄峰放光光譜。當溫度提升後，粉體之放光光譜則出現另一寬廣之紅光放射峰。與只能被紫外光激發的Tb3+窄峰不同，該紅光放射峰可在藍光激發下產生，顯示粉體可被用作為白光LED中之紅光螢光粉。另一方面，粉體在深紫外光激發後出現明顯的長餘輝特性，顯示該粉體亦可用作為蓄光材料。
於論文的第五章中，為了改善傳統固相法反應法製備Sr2Si5N8之缺點，利用新型化學氣相沉積(chemical vapor deposition, CVD)法製備Sr2Si5N8: Ce3+黃光螢光粉。透過CVD法反應性均勻之優點，大幅提升粉體之結晶性、粒徑分布均勻性以及發光亮度。在藍光激發下，Sr2Si5N8: Ce3+呈現一黃光放射峰，隨著Ce3+的濃度提高，粉體之放射峰由535 nm紅位移至556 nm，這是由於短波長放光的再吸收以及晶場強度的增加所致。
於論文的第六章中，結合能量轉移與CVD法之優點，製備光色可調之Sr2Si5N8: Ce3+, Eu2+螢光粉。在藍光激發下，Sr2Si5N8: Eu2+呈現一紅光放射峰，透過將Ce3+摻雜於Sr2Si5N8: Eu2+中可利用Ce3+→Eu2+的偶極-偶極能量轉移機制對其放光強度造成10%的提升。另一方面，將Eu2+摻雜於Sr2Si5N8: Ce3+時則因能量轉移導致Ce3+之放光強度隨Eu2+之摻雜濃度下降，此外放光亦從黃光移至紅光。在最後透過將粉體與藍光LED晶片進行封裝，成功製備出具備純白光色與高演色性之白光LED。
論文中製備出一系列的矽氧化物與矽氮化物螢光材料，並開發出一具備潛力之新型矽氮化物粉體製程，將合成出之新型螢光粉體與藍光LED晶片進行結合，製備出具備高演色性之白光LED，突破現有白光LED遭遇之困境。

關鍵字

矽氧化物 ； 矽氮化物 ； 螢光材料

並列摘要

To solve the drawbacks including high correlated color temperatures (CCTs) and low color-rendering index (CRI) values of conventional white light-emitting diodes (WLEDs), this thesis developed a series of silicate and nitridosilicate phosphors. The excitation and emission spectra of phosphors were controlled via the energy transfer process between luminescence centers. The crystallinity, particle size distribution, and brightness of phosphors were improved via a new synthesis process. Through the combination of the present phosphors with blue LED chips, WLEDs with high CRI values were fabricated.
ZnGd4Si3O13: Tb3+, Mn2+ silicate phosphors were synthesized in the first section of the thesis (Chapter 3). Under UV excitation, ZnGd4Si3O13: Mn2+ phosphors presented a red emission band, while ZnGd4Si3O13: Tb3+ showed several emission lines at 490, 544, 585 and 621 nm. The co-doping of Tb3+ ions into ZnGd4Si3O13: Mn2+ resulted in a 100% enhancement of the photoluminescence intensity for Mn2+ ions through a dipole-dipole energy transfer mechanism. On the other hand, the energy transfer process led to a decrease in Tb3+ emission as co-doping Mn2+ ions into ZnGd4Si3O13: Tb3+. In addition, obvious emission properties under the electron-beam excitation indicated the potential of the present phosphors for cathodoluminescence application.
In Chapter 4, for tuning the excitation wavelengths of phosphors, Sr2Si5N8 was selected as the host material for phosphors, and terbium ions were selected as the activators. The emission properties of phosphors were controlled through the variation of annealing temperatures. Sr2-xTbxSi5N8 prepared at low temperatures exhibited several narrow emission lines attributed to Tb3+ ions. When the heating temperatures were increased, another broad emission band in the red region was observed. The excitation spectra of the red emission band covered a wide region in the range from UVC to blue light, indicating the suitability of the present phosphors as the red phosphors for improving the color-rendering index of WLEDs. In addition, Sr2-xTbxSi5N8 phosphors exhibited long afterglow properties after UVC excitation. These results support that the present phosphors are also potential for the application in persistent luminescence devices.
To solve the drawbacks of the conventional solid-state reaction method, the chemical vapor deposition (CVD) process was developed to synthesize Sr2Si5N8: Ce3+ yellow phosphors in Chapter 5. The phosphors prepared via the CVD process showed higher crystallinity, more uniform particle size distribution, and better luminescence properties. Upon the blue light excitation, Sr2-xCexSi5N8 phosphors exhibited a broad yellow band owing to the 5d→4f transition of Ce3+ ions. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions.
In Chapter 6, the advantages of energy transfer and CVD method were combined to prepare Sr2Si5N8: Ce3+, Eu2+ phosphors with color-tunability. As the concentration of Ce3+ ions increased, the red emission intensity of Sr1.98-xCexEu0.02Si5N8 phosphors increased 10% due to the enhanced absorption and a dipole-dipole energy transfer from Ce3+ ions to Eu2+ ions. On the other hand, the energy transfer process led to a decrease in the yellow emission intensity of Sr1.94-yCe0.06EuySi5N8 phosphors with the doping of Eu2+ ions, and a shift of the emitting color from yellow to red. Finally, WLEDs with pure white CCT and high CRI values were successfully developed through the combination of blue LED chips with Sr1.98-xCexEu0.02Si5N8 phosphors.
In this thesis, a series of silicate and nitridosilicate phosphors and a potential synthesis process for nitridosilicate phosphors were developed. Through the combination of the present phosphors with blue LED chips, WLEDs with high CRI values were fabricated to overcome the drawbacks of conventional approach.

並列關鍵字

silicate ； nitridosilicate ； phosphor

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