發光二極體及量子剪裁應用之氧化鈰螢光粉製備與發光特性

Abstract

本論文第一部份首先討論CeO2球形內核之合成步驟，並且提出合成機制圖，將所合成之CeO2球進行熱重分析，以分析氧化鈰中殘留之有機物；以SEM分析其表面形貌以及CeO2粒徑大小，並且以TEM分析其晶體結構。後續使用沉澱法並利用沉澱劑在高溫會釋放氫氧根的特性，將不同濃度之Eu3+均勻包覆在球形氧化鈰表面上，後續進行高溫煆燒處理使Eu3+成功摻雜於CeO2主體晶格中。後續使用XRD分析CeO2:Eu3+之晶體結構，可得知摻雜Eu3+離子會使氧化鈰晶格膨脹和過量之Eu3+會出現Eu2O3相存在；使用SEM分析CeO2:Eu3+核殼結構之表面形貌，過量之Eu3+會在氧化鈰球形表面外單獨形成突起之形貌；使用掛載於TEM上之能量色散X-射線光譜分析，可以得知CeO2內核為一均勻球形，而Eu3+均勻分布於球形CeO2上；後續利用螢光光譜儀量測CeO2:Eu3+之光譜特性，此類螢光粉可以UV、藍光和綠光激發，放光波長位於橘紅光波段，並根據量測之結果討論CeO2晶體結構對發光特性之影響。 本論文第二部份先嘗試找出最適化之增感劑濃度，並量測其激發光譜與放射光譜，CeO2:Tb3+可以使用藍光激發，其放光波段位於黃綠光區間，所找出最適化之增感劑濃度為1 mol% Tb3+。後續使用XRD分析CeO2:Tb3+, Yb3+之晶體結構，可以得知以水熱法所合成之量子剪裁螢光粉屬於純相氧化鈰結構且沒有觀察到其他雜項出現。以SEM分析CeO2:Tb3+, Yb3+表面形貌以及觀察其粉體粒徑大小。使用365 nm之UV光源激發並以紅外光區間之偵測器量測放射光譜，可以得出Yb3+可有效地將UV波段之高能量光子轉換成位於低能量紅外光區之光子，並在976 nm可以觀察到Yb3+放射之波峰。

The first part in this thesis discussed the synthesis of CeO2 materials in a spherical form, and the corresponding synthesis mechanism was proposed in details. CeO2 spheres were then utilized to synthesize Eu3+ ions coated CeO2 phosphors via the precipitation technique. XRD analysis of the crystal structure of CeO2: Eu3+ shows that the doping of Eu3+ ions caused the lattice expansion and the Eu2O3 phase existed at high concentration of Eu3+. The surface morphology of the CeO2: Eu3+ core-shell structure was analyzed by SEM. The emission peaks were located in the orange-red wavelength band, CeO2: Eu3+ had intense emission due to the 5D0→7F1 (orange) or 5D0→7F2 (red) transition of Eu3+. The R/O emission ratio showed a linear increment with the Eu3+ concentration. The suitability of the present phosphors in warm white light-emitting diode was finally depicted in the chapter. In the second part, Tb3+ and Yb3+ ions co-activated CeO2 phosphors in octahedral shape were developed for quantum cutting applications to promote the photovoltaic efficiency. Firstly, the optimum concentration of sensitizer ions was estimated by varying the concentration of Tb3+ ions in CeO2: Tb3+ host. Then, Yb3+ ions are co-doped in the optimized host and the XRD analysis of the crystal structure of CeO2: Tb3+, Yb3+ indicated that the presence of pure phase. The near-infrared emission of CeO2: Tb3+, Yb3+ phosphors were observed using a 365 nm UV source. The present research concluded that Yb3+ could effectively convert high-energy photons in the UV band to the low-energy infrared region.