硫化鋅鎘量子點之製備、鑑定與應用;Preparation, Characterization and Application of ZnxCd1-xS Quantum Dots

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题名:	硫化鋅鎘量子點之製備、鑑定與應用;Preparation, Characterization and Application of ZnxCd1-xS Quantum Dots
作者:	陳宏碩;Chen,Hung-Shao
贡献者:	材料科學與工程研究所
关键词:	硫化鋅鎘;量子點;白光發光二極體;表面能態放射;量子效率;ZnCdS;quantum dots;white light emitting diodes;surface state emission;quantum yield
日期:	2015-07-21
上传时间:	2015-09-23 11:30:02 (UTC+8)
出版者:	國立中央大學
摘要:	發光二極體(light emitting diodes, LEDs)與螢光粉的複合元件由於具有高效率及技術可靠性，已成為具有潛力之節能方案，並在近年來受到廣泛的研究與討論，但傳統紅綠藍螢光粉因激發波段不同及其自我吸收效應，使其應用受限，相對的，量子點具有激發波段寬、發光波長可控性、高量子效率(quantum yield, QY)、被視為是可替代傳統螢光粉的新穎螢光粉材料，在本研究中藉由製備不同組成之三元ZnxCd1-xS量子點並將其與近紫外光LED結合形成LED元件，探討其封裝後之元件特性。本研究分為兩部分，第一部分為利用高溫有機金屬裂解法製備合金化ZnxCd1-xS量子點，探討其組成及反應時間對量子點能帶邊緣與表面能態放射對量子效率之關係。研究結果發現當鋅之理論組成(x)大於0.5時，量子點的放射光譜由兩個放射峰組成並涵蓋可見光範圍形成白光量子點，且當反應時間增加，光譜向長波長方向移動，而涵蓋可見光範圍的兩個放射峰分別為能帶邊緣與表面能態放射。實驗結果推測量子點的高表面鋅含量是表面能態放射產生的主要原因且鋅與鎘的氧化程度直接影響整體之量子效率。此外，當改變量子點組成由x=0.5增加至0.8時，其粒徑由3.6縮小至3.1 nm，量子效率由26提升至56 %，能帶邊緣放射波長由440藍移至410 nm。分別將鋅含量x=0.5及0.8之樣品在室溫下時效2個月，進行合金化ZnxCd1-xS量子點的穩定性評估，其量子效率分別由26與56降至20與37 %，顯示其具有良好的穩定性。由這個部分可以得知，白光量子點的產生是由於能帶邊緣、表面能態放射的共存與量子點之氧化所導致，且可藉由精確控制ZnxCd1-xS量子點的組成與結構得到。第二部分為元件特性之量測。將合金化ZnxCd1-xS量子點與矽膠及UV膠封裝混合後，以n-UV-LED為激發源結合而成的元件，探討量子點的添加量對元件色度座標(Commission international de I’Eclairage, CIE)、平均演色性指數(general color rendering index, CRI)、相關色溫(correlated color temperature, CCT)及發光效率(luminous efficiency)之影響。在定電流20 mA之元件特性量測結果中發現，當Zn0.8Cd0.2S量子點與矽基封裝膠的比例為1:10時，可得到CIE位於(0.36,0.33)，CCT為4200 K，發光效率為4.12 lm/W，CRI為86之白光LED。當Zn0.8Cd0.2S量子點與UV膠混合比例為1:1時，可得CIE= (0.34,0.32)，CCT為5000 K，發光效率為11.93 lm/W，CRI為87之白光LED。由以上結果得知，合金化ZnxCd1-xS量子點藉由調控組成及其與封裝膠的配比，可以有效調控CIE、CCT、CRI，得到高演色性的白光LED元件。 ;In recent years, phosphor-converted light emitting diodes (PC-LEDs) have attracted a significant amount of attention due to their high efficiency and reliability. Since the application of traditional R/G/B phosphor is limited by the narrow excitation band, different excitation wavelength and self-absorption problems, alternative materials should be developed. Because quantum dots (QDs) possess controllable emission wavelength, broad excitation band and high quantum efficiency (QY), they are regarded as promising candidates to replace traditional phosphors. In this study, a series of colloidal ternary semiconductor ZnxCd1-xS QDs have been prepared and the property of devices, which are formed by combination of QDs with n-UV-LED has been investigated. This study includes two major parts. The first one is the effects of local atoms/valence band structures and surface/chemical compositions on QY of ZnxCd1-xS QDs. The results show that when Zn content is higher than 0.5, the emission wavelength involves entire visible spectra range with two emission wavelengths, caused by band-edge and surface state emission. Besides, both two peaks move to longer wavelength with increasing the reaction time. The surface state emission is affected by the oxidation degree of Zn and Cd and the formation of Zn-rich surface. In addition, the particle size changes from 3.6 to 3.1 nm, QY increases from 26 to 56 % and the peak of band-edge emission moves from 440 to 410 nm with increasing Zn content from 0.5 to 0.8, respectively. When the sample is aged at room temperature for 2 months, the QY decreases from 26 to 20 % and 56 to 37 % for Zn0.5Cd0.5S (Zn0.5) and Zn0.8Cd0.2S (Zn0.8), respectively. The white QDs (WQDs) can be obtained by controlling the compositions and structure of ZnxCd1-xS QDs due to the coexistence of band-edge and surface state emission and oxidation. The second part focuses on the devices fabrication and measurement. Zn0.5 or Zn0.8 QDs are dispersed in silicone (Si) and UV resin under desired ratios. When the ratio of Zn0.8 QDs and Si is 1:10 and forward current is set at 20 mA, the chromaticity coordinates (Commission international de I’Eclairage, CIE) is (0.36,0.33), correlated color temperature (CCT) is 4200 K, color rendering index (CRI) is 86 and luminous efficiency is 4.12 lm/W. On the other hand, for the ratio of Zn0.8 QDs and UV resin is 1:1, the CIE, CCT, CRI and luminous efficiency are (0.34,0.32), 5000 K, 87 and 11.93 lm/W, respectively. Based on above results, we can conclude that QD-based WLED device with a high CRI can be obtained by controlling the compositions and blending content of ZnxCd1-xS QDs.
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