Synthesis and Luminescence Characterization of Novel Phosphors for White-light-emitting diodes
此外，M5B(WO4)4-x(MoO4)x (M = I, J, K)系列螢光材料中， J5B(WO4)4-x(MoO4)x為最佳化組成，其呈現最強的紅光放射。當鎢/鉬莫耳比例為1：1時，其5D0→7F2之紅光放射呈現最高強度。另外，J5B(WO4)2(MoO4)2因具有特殊結構，已被證明為一種不具濃度消光效應的優良螢光粉。由J5B(WO4)2(MoO4)2所封裝成的白光發光二極體，其平均Ra值為82.3，遠高於由商品La2O2S:Eu3+所製成白光發光二極體Ra值(70.8)。飽和紅Ra值可由-15.20（La2O2S:Eu3+所封裝之白光發光二極體），提升為82.89（J5B(WO4)2(MoO4)2所封裝之白光發光二極體）。
A3B2C3(WO4)8-x(MoO4)x:Eu3+及G2(WO4)3-x(MoO4)x:Eu3+皆能吸收近紫外光，在波長394nm光源激發下，產生強烈的紅光放射。上述兩材料，5D0→7F2躍遷之最佳強度皆發生於鎢/鉬莫耳比例為1：1時。此外，A3B2C3(WO4)8-x(MoO4)x:Eu3+系列螢光粉色座標皆為(0.66, 0.33)，而G2(WO4)3-x(MoO4)x:Eu3+系列螢光粉色座標則為(0.67, 0.33)，上述螢光材料相對輝度均較紅光商品Y2O2S:Eu3+或La2O2S:Eu3+為高。
本研究亦探討MAxOyN:Eu2+ (M = I, J, K)系列螢光材料。其中，KAxOyN:Eu2+為最佳組成，其放射波長為444nm寬帶藍光。化學組成對KAxOyN:Eu2+,Mn2+的發光特性也被進一步探討。因Eu2+放射光譜與Mn2+激發光譜重疊，我們推論Eu2+和Mn2+間存在能量轉移現象。隨著Mn2+摻雜量增加，波長位於513 nm之Mn2+放射強度逐漸增強，而相對地Eu2+放射強度則隨之逐漸減弱。Eu2+→Mn2+的能量轉移效率也被發現隨Mn2+摻雜量增加而提升。|
We have successfully synthesized four types of intense red-emitting tungsto-molybdates (all for Eu3+-doped luminescent materials), and one type of emission-tunable phosphor (Eu2+/Mn2+-codoped) via solid-state reaction technique at high temperature. First, AB(WO4)2-x(MoO4)x have been investigated and reported. When the molybdenum content is increased, the lithium europium double tungsto-molybdate shows stronger red emission at 615nm by exciting at near-UV wavelength of 394 nm. The CIE chromaticity coordinates were found to be (0.66, 0.33) for AB(MoO4)2 and it reached the same level as the commodity phosphor Y2O2S:Eu3+. The color-rendering index (Ra) value of the WL-LED based on AB(MoO4)2 was found to be 67.8, approaching that (Ra~70.8) of the other WL-LED based on the commodity of La2O2S:Eu3+. Specifically, the CRI-No.9 value showing color reproduction in the red region has been improved from -15.20 to 53.05 for the WL-LEDs using AB(MoO4)2 as the red-emissive component. Subsequently, we have investigated the luminescence of a series of M5B(WO4)4-x(MoO4)x (M = I, J, K) phosphors and discovered that J5B(WO4)4-x(MoO4)x exhibit the most intense red-emission among the three investigated. The intensity of 5D0→7F2 transition reaches a maximum when the relative ratio of W/Mo is 1:1. In addition, J5B(WO4)2(MoO4)2 has also been proved to be a good phosphor showing no concentration quenching because the special structure of it. The color-rendering index (Ra) of a typical WL-LED based on J5B(WO4)2(MoO4)2 was found to be 82.3, higher than that (i.e., Ra~70.8) obtained for the WL-LED fabricated using the commodity of La2O2S:Eu3+. Particularly, the CRI-No.9 value, showing color reproduction in the red region, has been improved from -15.20 to 82.89. Both A3B2C3(WO4)8-x(MoO4)x:Eu3+ and G2(WO4)3-x(MoO4)x:Eu3+ show excitation band around near-UV region, and enhanced red emissions under 394 nm light excitation. The two kinds of phosphors exhibit equally that the intensity of 5D0→7F2 transition reaches a maximum when the relative ratio of W/Mo is 1:1. The CIE chromaticity coordinates were found to be (0.66,0.33) for all series of A3B2C3(WO4)8-x(MoO4)x:Eu3+, whereas that were found to be (0.67,0.33) for all G2(WO4)3-x(MoO4)x:Eu3+ phosphors. For each of the phosphors, the relative luminance was found to be larger than either Y2O2S:Eu3+ or La2O2S:Eu3+. We have also studied on series of MAxOyN:Eu2+ (M = I, J, K) phosphors. We have observed that KAxOyN:Eu2+ exhibit the broad blue emission band centering at 444 nm among the three investigated. The effect of chemical compositions on the luminescence properties of KAxOyN:Eu2+,Mn2+ has also been investigated. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing spectral overlap between the emission band of Eu2+ and the excitation transitions of Mn2+. With increasing Mn2+ content, the PL intensity at around 513 nm of Mn2+ was observed to increase systematically, whereas that of Eu2+ was discovered to decrease gradually. The energy transfer efficiency (ηT) from Eu2+ to Mn2+ has been found to increase gradually with increasing Mn2+ dopant contents.
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