應用於白光LED之高量子產率無稀土螢光材料

Abstract

目前高效率白光LED多數是使用稀土型螢光材料來實現，然而稀土之開採對環境有相當嚴重的迫害。雖有量子點被提出當成可能之替代方案，但高效率量子點裡皆含有重金屬鎘，對環境也是有相當大的隱憂，且量子點強烈的量子侷限效應，使其激發波長多被限制在紫外光，難以與現行的高效率藍光LED整合。本研究中，我們成功研發出一種合成ZnSe:Mn奈米粒子的技術，能解決量子侷限效應的問題並達成環保的目的。 研究內容可分為三個部份，第一部份我們成功地製作出量子侷限效應極小之ZnSe:Mn奈米粒子，使其最佳吸收在445 nm以上的波段，能與商用藍光LED結合。並於第二部分分別從陽離子濃度、Mn離子含量、陰離子型界面活性劑、檸檬酸鈍化奈米粒子表面等方式提高材料之量子效率與發光亮度，目前最高之量子效率可達84.5 %。我們也於第三部分則探討潤洗溶劑之選擇、乾燥時間與真空度對奈米粒子之乾燥製程的影響，成功地乾燥成無氧化變質現象之粉體。最後將ZnSe:Mn奈米粒子與商用高效率之藍光LED整合並探討流明之量測，也提出藉由燈具設計、濃度與厚度之控制改善反向散射的情況提升發光效率。 本研究所提出的方式可成功製作能與商用藍光整合之ZnSe:Mn奈米粒子，能有效率地將藍光轉換成橘黃光且可利用低溫溶液製程合成，更重要的是此方式不再依賴高汙染之稀土元素或重金屬鎘，具有相當大的潛力成為新世代應用於白光LED之螢光材料。

Current available methods for WLEDs are mostly based on expensive rare-earth elements (REEs) doped phosphors, which would cause a tremendous harm to the environment. Although quantum dots (QDs) and nanocrystals (NCs) have been proposed as promising alternatives, these materials still have environmental concerns due to containing cadmium. Moreover, the strong quantum confinement effect in these nanoscale materials causes their efficient excitation wavelength to be limited in UV region, and this situation hinders these nanomaterials from integrating with commercial blue-LEDs. In this work, we develop a novel technique to synthesize environmental benign ZnSe:Mn nanoparticles with little quantum-confinement effect. The research can be separated into three parts. In the first part, we successfully synthesized ZnSe:Mn nanoparticles with little quantum-confined effect. The excitation wavelength of the nanoparticles is larger than 445 nm, which matches the commercial blue LEDs. In the second part, we aim to improve the efficiency of the nanoparticles. By optimizing the concentration of cations and Mn2+, and adding surfactant and citric acid, the quantum efficiency can reach 84.5%. In the third part, we focus on enhancing the drying process of the nanoparticles by changing rinse solvent, drying time, and drying pressure. Finally, we measure the luminous efficacy of the nanoparticles. Therefore, ZnSe:Mn nanoparticles featuring rare-earth-free and cadmium-free can sever as another promising candidate for luminescence conversion of white-LEDs.