現今全球節能減碳議題中，開發高效率的白光LED作為照明工具是一致的研究重點與發展方向，而製造出特性佳的白光LED之關鍵就在於高效率及高演色性的螢光粉。釔鋁石榴石(YAG)螢光粉因具有高量子效率、合成簡單與成本低廉等優勢，向來為搭配藍光LED製作白光LED的主流材料。然而，由於YAG:Ce螢光粉缺乏紅色放光波段，YAG:Ce黃色螢光粉搭配藍光LED所製作之白光LED存在演色性不足的缺點。
為了開發出高量子效率與高演色性之YAG:Ce螢光粉以提升封裝後白光LED之發光效率與演色性，本研究透過二階段煆燒固態反應法與成分改質分別合成出高量子效率與高演色性之YAG:Ce螢光粉。在合成高量子效率YAG:Ce螢光粉方面，利用添加不同助熔劑硼酸與氟化鋇以降低煆燒溫度及促進純YAG相之生成，我們發現粉體形貌對於螢光粉之量子效率的關鍵影響，並進一步藉由顆粒成長機制探討使用不同助熔劑造成YAG:Ce粉體形貌差異的原因。在合成高演色性YAG:Ce螢光粉方面，本研究利用鎂、矽分別取代YAG中的八配位與四配位之鋁[Y2.95Al5-2y(Mg, Si)yO12:0.05Ce3+，YAMSG:Ce]，使得YAG主體晶格扭曲且共價性增加，促使YAG:Ce之發光光譜往長波長移動，產生紅色波段之螢光。
為了證明上述高量子效率與高演色性YAG:Ce螢光粉之實用性，本研究利用遠距式塗佈技術將高量子效率YAG:Ce封裝於主發光波長為450 nm之藍光LED製作出白光LED，並進一步與商用YAG:Ce螢光粉以相同技術封裝之白光LED進行發光效率與演色性之比較。為了合理化白光LED之特性比較，本研究將螢光膠層厚度固定於 ~600 μm，並將色溫分別控制於~5500 K與~4500 K以製作YAG:Ce基與YAMSG:Ce基白光LED。在350 mA驅動下，最佳化YAG:Ce基白光LED的發光效率(77.2 lm/W)較商用YAG:Ce螢光粉所製作之白光LED(70.87 lm/W)提升了9%；而以最佳化YAMSG:Ce螢光粉取代商用YAG:Ce螢光粉則將白光LED之演色性從68提升至81。

In view of the global problem of energy saving and carbon reduction nowadays, to develop efficient white light-emitting diodes (WLEDs) as the lighting source has become the concurrent research point and development direction. And the efficient phosphor with the high color rendering index (CRI) plays a key role to fabricate a WLED with the excellent performance. Considering that the yttrium aluminum garnet (YAG) phosphor has advantages such as high quantum efficiency, simple synthesis procedure, and low cost, it has always been the mainstream material in conjunction with the blue-LED chips for the fabrication of WLEDs. However, the lack of red components in its emission spectrum leads to the disadvantage of insufficient CRI for a yellow phosphor YAG:Ce-based WLED with a blue-LED chip.
In order to develop YAG:Ce phosphors with high quantum efficiency and high CRI for enhancing the luminous efficiency and CRI of WLEDs, we sought to synthesize high quantum efficiency YAG:Ce and high CRI YAG:Ce on the basis of the two-step calcined solid state reaction method and composition modification, respectively. On the part of synthesizing highly efficient YAG:Ce powders, an attempt was made to reduce the required calcined temperature and expedite the formation of pure YAG phase with the addition of H3BO3 and BaF2 as fluxes. We found that the morphology of YAG:Ce particles is critical to the quantum efficiency of phosphors, and the mechanism of the particle growth was used to explain why the selection of fluxes can cause the difference in YAG:Ce morphologies. On the part of synthesizing high CRI YAG:Ce powders, an attempt was made to cause the lattice distortion and increase the covalence of YAG:Ce by replacing octahedral Al3+ and tetrahedral Al3+ with Mg2+ and Si4+ ions, respectively [Y2.95Al5-2y(Mg, Si)yO12:0.05Ce3+，YAMSG:Ce]. Such composition modification is expected to shift the emission spectrum of YAG:Ce to the longer wavelength, and therefore the increase of red components in the spectral range.
To evaluate the feasibility of the said high quantum efficiency and high CRI YAG:Ce phosphors, these phosphors were combined with the 450-nm blue LEDs by using the remote coating technology. And the luminous efficiency and CRI of our fabricated WLEDs were further compared with those of the commercial YAG:Ce-based WLED under the same phosphor configuration. To validate the comparison among optical properties of these WLEDs, the thickness of the phosphor layers was kept at ~600 μm; moreover, the YAG:Ce-based and YAMSG:Ce-based WLEDs were fabricated under the correlated color temperature (CCT) of ~5500 K and ~4500 K, respectively. Under the drive current of 350 mA, the luminous efficiency of the commercial YAG:Ce-based WLED (70.87 lm/W) was enhanced by 9% compared to that of the WLED using optimized YAG:Ce phosphors (77.2 lm/W). Additionally, the CRI of the commercial YAG:Ce-based WLED was improved from 68 to 81 with the substitution of the optimized YAMSG:Ce for the commercial YAG:Ce.

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