新穎高飽和紅光四價錳摻雜氟化物螢光粉之製備、發光特性鑑定及其照明之應用

Abstract

為改善傳統白光發光二極體 (WLED) 高色溫 (CCT > 4000 K) 與低演色性 (Ra < 80) 之缺失，近年來供暖白光LED封裝與液晶電視背光源所使用之高飽和紅光Mn4+螢光體逐漸興起。Mn4+摻雜氟化物在藍光及紫外光激發下，能放射窄波形紅光，其寬帶激發源自於Mn4+ (d3) 4A2g→4T2g及4A2g→4T1g兩躍遷，其所放射線形紅光則源自於2Eg→ 4A2g躍遷。 本研究以K2MnF6作為Mn4+的來源，透過高效陽離子交換法成功合成Rb2TiF6:Mn4+、Cs2ZrF6:Mn4+、Li2SiF6:Mn4+及Li2TiF6:Mn4+ 等四種高飽和紅光氟化物螢光體。上述氟化物主體晶格中，Mn4+ 所取代者為八面體配位的Ti4+、Si4+ 或Zr4+ 格位，我們利用X光粉末繞射、螢光、漫反射與熱消光光譜及掃描式電子顯微鏡進行螢光體之晶體結構、光學與發光特性及色度學特性分析鑑定，同時進行WLED封裝探討其應用潛力，研究結果顯示Rb2TiF6:Mn4+ 具有極高量子效率及熱消光性，極具應用於暖白光LED之潛力，其在波長 630 nm的窄波形紅光可用以改善白光LED色溫過高及演色性不足之缺失。

Being able to circumvent the problems of high color temperature (CCT > 4000K) and low color rendering index (CRI < 80) of conventional YAG-type white light-emitting diodes (WLEDs) used for lighting, Mn4+-activated red-emitting fluorides have been emerging as potential red phosphors for warm WLEDs due to their unique optical properties. In this research, we have successfully synthesized four novel fluoride phosphors, Rb2TiF6:Mn4+, Cs2ZrF6:Mn4+ and Li2XF6:Mn4+ (X= Ti and Si), through cation-exchange method using K2MnF6 as the Mn4+ source. The crystal structures and luminescent properties of the above phosphors were well investigated using X-ray powder diffraction (XRD), photoluminescence excitation and emission spectra (PL/PLE), temperature-dependent PL spectra, and decay measurements. Mn4+- activated red-emitting fluoride phosphors can be excited over a broad range from UV to blue region (300-550nm), attributed to the 4A2g → 4T2g and 4A2g → 4T1g transitions of Mn4+, and present highly-saturated red emission peak at around 630 nm, corresponding to the 2Eg → 4A2 transition of Mn4+. In addition, under excitation at 450 nm Rb2TiF6:Mn4+ exhibits decent thermal-quenching stability and high quantum efficiency (65.7%) relative to that of commercial K2SiF6:Mn4+. Furthermore, we also fabricated a WLED lamp using Rb2TiF6:Mn4+ as the red-emitting phosphor, Y3Al5O12:Ce3+ (YAG) and a 450 nm InGaN-based blue LED chip driven by 100 mA current. Our research results show that Rb2TiF6:Mn4+ can be one of the most promising red phosphor for warm-white LED.