新穎磷酸鹽螢光粉之製備、發光特性與能量轉移之研究

Abstract

本研究成功製備三種分別應用於氙燈、七種顏色可調色調及三種適用於紫外或近紫外光發光的白光二極體的黃光磷酸鹽螢光粉。 第一章為本論文架構與目前螢光燈及白光發光二極體的研究背景及現況，探討敏化劑與活化劑的發光特性與能量轉移現象，另外設計與評估出研發新穎磷酸鹽螢光粉白光並且以此為主軸提出本論文研究之動機。 第二章描述發紫外光Ca9Y(PO4)7:Ln3+ (Ln = Ce, Gd, Pr)螢光材料之製備與發光特性分析。其中Ca9Y(PO4)7:Ce3+呈現寬帶的UVA波段發光，其發射峰波峰值為346 nm；Ca9Y(PO4)7:Gd3+呈現線性UV B波段發光，其發射峰波峰值為312 nm，而Ca9Y(PO4)7:Pr3+則呈現兩寬帶的UVC波段發光，其發光波長範圍在230 ~ 340 nm 之間，上述螢光體在172 波長的激發下， 均呈高發光效率及熱穩定性。 第三章詳述發紅光(Ca9Y(PO4)7:Ce3+,Mn2+ 螢光粉之固態法合成。其Ce3+ → Mn2+能量轉移機制經確認為共振型電偶極－四極交互作用，同時計算出Ce3+和Mn2+間能量轉移理論臨界距離為13.45 Å。以Ca9Y(PO4)7:0.15Ce3+,0.1Mn2+ 封裝為紅光螢光燈時，其色座標值為(0.54, 0.32)。 第四章描述綠光Ca9Y(PO4)7:Ce3+,Tb3+螢光粉之發光特性鑑定，本研究確認Ce3+ → Tb3+的能量轉移機制為電偶極－偶極交互作用，其中Ce3+和Tb3+間的能量轉移臨界距離為6.88 Å；然而Ca9(Y0.35Ce0.15Tb0.5)(PO4)7比商用綠光螢光粉LaPO4:Ce3+,Tb3+具有較高的熱穩定性，研究結果顯示此螢光材料適用於綠光螢光燈。 第五章描述(Ca9Y(PO4)7:Ce3+,Eu2+螢光粉之合成，其發光光譜呈現兩放射峰，其波長一源自於Ce3+離子為342 nm；而另一源自於Eu2+離子之發光，其波長為492 nm。利用能量轉移方式，此螢光粉發光顏色可從紫光調至藍綠光；藉由螢光衰變實驗可決定Ce3+ → Eu2+能量轉移機制為共振型態的電偶極－偶極交互作用，本研究並且利用濃度淬滅和光譜重疊法算出Ce3+和Eu2+間能量轉移的臨界距離為30.7 Å。 第六章描述單一組成Ca9Y(PO4)7:Eu2+,Mn2+白光螢光粉之製備與發光特性鑑定。在Ca9Y(PO4) 7主體中，Eu2+ → Mn2+能量轉移機制為共振型態的電偶極－四極交互作用，在250 ~ 440 nm 間波長激發下，藉由Eu2+與Mn2+相對比例之調控，其顏色可從藍綠光微調白光甚至到紅光。 第七章描述發光色調可調變的Ca9La(PO4)7:Eu2+,Mn2+螢光粉之製備與特性鑑定。藉由Eu2+與Mn2+之間共振型態的電偶極－四極型的能量轉移方式，其色度可從綠光微調至黃光甚至到紅光， Eu2+和Mn2+間能量傳遞臨界距離經計算結果為11.36 Å。將Ca9La(PO4)7:Eu2+,Mn2+封裝成白光發光二極體，其色座標值為(0.35, 0.31)、演色係數為91.5、色溫為4496 K，屬於中色溫白光。 第八章描述兩種放光顏色可調控的(Ca,Mg,Sr)9Y(PO4)7:Eu2+ 和(Ca0.5Sr0.5)9Y(PO4)7:Eu2+,Mn2+螢光粉。藉由結晶場的改變與Eu2+和Mn2+之間能量轉移之調控，其色度可從藍光微調至綠光甚至到紅光，Eu2+ → Mn2+能量轉移機制為共振型態的電偶極－偶極交互作用，同時計算出Eu2+和Mn2+之間能量轉移的臨界距離經結果計算為11.09 Å。將此螢光粉封裝成三波長白光發光二極體，測得其色座標值為(0.314, 0.348)、演色係數為87.4，且色溫為6303 K。 第九章描述Ca9Gd(PO4)7:Eu2+,Mn2+單一組成白光螢光粉之製備與螢光特性鑑定。本論文藉由Eu2+和Mn2+之間共振型態的電偶極－四極型的能量轉移，將色度由藍綠光微調至白光甚至到紅光。以Ca9Gd(PO4)7:Eu2+,Mn2+封裝成單一組成白光發光二極體，測得其色座標值為(0.312, 0.327)，色溫為6569 K。 第十章描述Sr8MgSc(PO4)7:Eu2+螢光粉之製備、晶體結構和發光特性鑑定。本研究利用近紫外發光二極體晶片搭配發黃光的(Sr0.99Eu0.01)8MgSc(PO4)7和藍光的BaMgAl10O17:Eu2+螢光粉混合成白光，其色座標值為(0.33, 0.34)，色溫為5614 K屬於中色溫白光，演色係數為96.7。 第十一章描述黃光Sr8MgY(PO4)7:Eu2+和Sr8MgLa(PO4)7:Eu2+螢光粉之製備與螢光特性鑑定。Sr8MgY(PO4)7:Eu2+和Sr8MgLa(PO4)7:Eu2+在400 nm近紫外波長激發下，前者呈現二處發光波長：一為518 nm，另一為610 nm；而後者呈現在611 nm放射峰，且此兩螢光粉較黃光 (Ba,Sr)2SiO4 (570 nm)商品具有較高的熱穩定性。將Sr8MgY(PO4)7:Eu2+和Sr8MgLa(PO4)7:Eu2+螢光粉分別封裝成兩種白光發光二極體，其中使用Sr8MgY(PO4)7:Eu2+螢光粉者，其色座標值為(0.348, 0.357)，色溫為4705 K屬於中色溫白光，演色係數為95.375；使用Sr8MgLa(PO4)7:Eu2+螢光粉者，其色座標為(0.365, 0.328)，色溫為4100 K屬於暖白光，演色係數為91.75。 最後則本論文歸納所開發的磷酸鹽螢光粉之發光特性、能量轉移機制和潛在應用與總結，並提示未來工作項目。

We have successfully synthesized three ultraviolet-radiative phosphors for applications in xenon lamps, seven emission color-tunable phosphors, and three yellow-emitting phosphors for applications in UV/NUV LEDs. Chapter 1 introduces the framework of this thesis and the research background of fluorescent lamp and white light-emitting diodes. By the literature review of luminescence properties and energy transfer phenomena of sensitizer and activator, to present the design and appraise of novel whitlockite-type phosphate phosphors, and then elaborates the motivations. Chapter 2 describes the preparation and luminescence characterizations for ultraviolet-radiating Ca9Y(PO4)7:Ln3+ (Ln = Ce, Gd, Pr) phosphors. The Ca9Y(PO4)7:Ce3+ phosphor emits UVA light in the form of one broad emission band centered at 346 nm; the Ca9Y(PO4)7:Gd3+ phosphor shows a strong sharp UVB emission band at 312 nm and the Ca9Y(PO4)7:Pr3+ shows two broad UVC emission bands peaking in the range of 230 ~ 340 nm. Under 172 nm VUV radiation excitation, we have demonstrated that Ca9Y(PO4)7:Ln3+ (Ln = Ce, Gd, Pr) phosphors exhibit high emission efficiency and excellent thermal stability. In Chapter 3, a series of new broad band deep red-emitting phosphors Ca9Y(PO4)7:Ce3+,Mn2+ have been synthesized by a high-temperature solid-state reaction. The energy transfer mechanism from Ce3+ to Mn2+ was via an electric dipole-quadrupole interaction and the critical energy transfer distance was found to be 13.45 Å. The Ca9Y(PO4)7:0.15Ce3+,0.1Mn2+ phosphor can be used to fabricate cold cathode fluorescent lamps and was found to emit red light with CIE coordinates of (0.54, 0.32). In Chapter 4 we have investigated the luminescence of a series of green-emitting Ca9Y(PO4)7:Ce3+,Tb3+ phosphors. The energy transfer from Ce3+ to Tb3+ has been demonstrated to be a dipole-dipole mechanism with a critical distance of 6.88 Å. The thermal quenching stability of the composition-optimized Ca9(Y0.35Ce0.15Tb0.5)(PO4)7 was found to be higher than that of LaPO4:Ce3+,Tb3+ commodity. Our results demonstrated that Ca9Y(PO4)7:Ce3+,Tb3+ can serve as a potential green-emitting phosphor for fluorescent lamp application. Chapter 5 describes a series of Ce3+- and Eu2+-coactivated Ca9Y(PO4)7 phosphors synthesized by high-temperature solid-state reactions. The Ca9Y(PO4)7:Ce3+,Eu2+ phosphor showed two emission bands at 342 nm and 492 nm, respectively. Through an effective resonance-type energy transfer, the Ca9Y(PO4)7:Ce3+,Eu2+ phosphors exhibit a systematically varied hue from ultraviolet to bluish-green. The energy transfer has been demonstrated to be a resonant type via a dipole-dipole mechanism and the critical distance was found to be about 30.7 Å. Chapter 6 describes the preparation and luminescence characterizations for single-composition emission color-tunable Ca9Y(PO4)7:Eu2+,Mn2+ phosphors. The energy transfer from Eu2+ to Mn2+ in Ca9Y(PO4)7 host matrix was studied and demonstrated to be a resonant type via a dipole-quadrupole mechanism. By properly tuning the ratio of Eu2+/Mn2+, white light with varied hues can be generated in pre-designed Ca9Y(PO4)7:Eu2+,Mn2+ phosphors under the excitation at 250 ~ 440 nm. Chapter 7 portrays a series of emission color-tunable Eu2+/Mn2+ co-activated Ca9La(PO4)7:Eu2+,Mn2+ phosphors, which exhibit varied hues from green through yellow, and eventually to red by resonance-type dipole-quadrupole of Eu2+ to Mn2+ energy transfer and the Eu2+–Mn2+ critical distance was estimated to be 11.36 Å. A white LED with CIE coordinates of (0.35, 0.31), excellent CRI of 91.5 and lower correlated color temperature of 4496 K was fabricated. Chapter 8 discusses a series of emission color-tunable (Ca,Mg,Sr)9Y(PO4)7:Eu2+ and (Ca0.5Sr0.5)9Y(PO4)7:Eu2+,Mn2+ phosphors whose emission wavelengths could be tuned from blue to green and eventually to red by tuning the crystal field splitting and energy transfer. The energy transfer mechanism has been demonstrated to be an electric dipole-quadrupole interaction and the Eu2+–Mn2+ critical distance was calculated to be 11.09 Å. A trichromatic white light-emitting diode with a CCT of 6303 K, CRI of 87.4, and CIE coordinates (0.314, 0.348) close to those of ideal white-light was fabricated using (Ca,Mg,Sr)9Y(PO4)7:Eu2+, Mn2+ phosphor. Chapter 9 delineates the preparation and luminescence characterizations for single-phased white light-emitting Ca9Gd(PO4)7:Eu2+,Mn2+ phosphors. By tuning the Eu2+/Mn2+ ratio, we have varied the emission hue from bluish-green to white-light and eventually to red via electric dipole-quadrupole energy transfer of Eu2+ → Mn2+. Combining a 380 nm NUV chip and a white-emitting (Ca0.973Eu0.007Mn0.02)9Gd(PO4)7 phosphor produced a white-light NUV LED, exhibiting the CIE coordinates of (0.312, 0.327) and CCT of 6569 K. Chapter 10 discusses that a yellow-emitting Eu2+-activated Sr8MgSc(PO4)7:Eu2+ phosphor whose crystal structure was refined and determined by Rietveld refinement method. In addition, white-light NUV LEDs were fabricated by using a phosphor blend of composition-optimized yellow-emitting (Sr0.99Eu0.01)8MgSc(PO4)7 and blue-emitting BaMgAl10O17:Eu2+ commodity pumped with a 400 nm NUV chip and the CIE coordinates, CCT and excellent CRI were found to (0.33, 0.34), 5614 K and 96.7, respectively. Chapter 11 depicts the preparation and luminescence characterization for yellow-emitting Sr8MgY(PO4)7 and Sr8MgLa(PO4)7 phosphors. Upon excitation at 400 nm, the Sr8MgY(PO4)7:Eu2+ and Sr8MgLa(PO4)7:Eu2+ phosphors exhibit strong yellow emissions centered at 518, 610, and 611 nm and they show higher thermal stability than (Ba,Sr)2SiO4 (570 nm) commodity phosphors. For Sr8MgY(PO4)7:Eu2+ and Sr8MgLa(PO4)7:Eu2+ phosphors, white-light NUV LEDs with the CIE coordinates of (0.348, 0.357) and (0.365, 0.328), CCT of 4705 K and 4100 K, and excellent CRI of 95.375 and 91.75, respectively, were fabricated. Final chapter summarizes and compares the luminescence properties, energy transfer mechanism, and applications for all of the phosphors investigated in this work and draws an overall conclusion.