|Abstract: ||半導體奈米晶因其具有特殊的可調性以及在發光二極體(light emitting diodes, LEDs)、雷射、生物標籤等領域的應用，在近幾年受到廣泛的研究與討論。一般商業化的發光二極體主要是由藍光晶片與傳統螢光粉所製成，但傳統螢光粉具有散射效應、低演色性以及多重吸收效應等缺點，因此光學性質可藉由顆粒大小與組成來調控的半導體奈米晶被視為是可取代傳統螢光粉的材料。|
本研究分為兩部分，在第一部分，藉由化學合成法製備高效能之白光ZnCdS奈米晶，白光的產生來自於能帶邊緣與表面能態之放射，並探討量子效率(quantum yield, QY)與不同表面配位基對奈米晶表面造成的鈍化效應之關係，由實驗結果可發現利用短碳鏈的烯類(decene, DE)作為表面配位基，ZnCdS奈米晶之量子效率可達到99.0 %，主要由於奈米晶表面具有較高的鋅含量以及較少的氧化物所致。
在第二部分中，使用第一部分製備的ZnCdS奈米晶與UV晶片為激發光源製備之白光LED元件，而元件之色度座標(Commission international de I’Eclairage, CIE)、演色性指數(color rendering index, CRI)、相關色溫(correlated color temperature, CCT)及發光效率(luminous efficiency)可藉由使用不同放光波長的ZnCdS奈米晶，表面配位基，反應時間，奈米晶含量及封裝方式來控制。研究結果指出，使用單一ZnCdS白光奈米晶為螢光粉並以UV晶片為激發光源，可得到CIE=(0.32, 0.30)，CRI=82，CCT=6811 K，發光效率為4.26 lm/W之白光LED，此結果顯示出ZnCdS奈米晶具有作為白光螢光材料之潛力。
;In recent years, II-VI semiconductor nanocrystals (NCs, also called quantum dots, QDs) have received great attention due to their novel tunable properties and their potential applications in light emitting diodes (LEDs), lasers and biological labels. The commercial LEDs are based on the blue LED chips and traditional phosphors, which suffer from the scattering, low color rendering index (CRI) and the reabsorption problem of the multiphase phosphors. Since the optical properties of semiconductor NCs can be tuned in the visible light range by controlling not only the particle sizes but also the compositions of the NCs, NCs are regarded as promising materials to replace traditional phosphors in the fabrication of LEDs. In this study, the colloidal ternary semiconductor ZnCdS NCs with wide emission and high quantum yields (QYs) have been prepared and used as nanophosphors in white light emitting diodes (WLEDs). The materials and devices properties of ZnCdS NCs have been investigated.
This study includes two major parts. In the first part, the highly effective ternary ZnCdS NCs with white light emission have been synthesized successfully. The white light emission results from the combination of band edge and broad surface state emissions. The correlation between QYs and the passivation effects of alkenes with different carbon chain lengths used as surface ligands of ZnCdS have been explored. The QY of ZnCdS NCs prepared by decene (DE) can reach to 99.0 %, attributed to the formation of a metallic Zn-rich surface and the less oxidation of Zn and Cd on the NCs surface.
In the second part, the WLEDs based on the ZnCdS NCs and UV chips have been prepared. The optical properties of ZnCdS NCs-based WLEDs including Commission Internationale de l’Eclairage (CIE) chromaticity coordinates, correlated color temperature (CCT), CRI and luminous efficiency can be adjusted by the various ZnCdS NCs, using different carbon chain lengths of alkenes as surface ligands, reaction time, NCs contents and encapsulation methods. The optimal conditions of CIE, CRI, CCT and luminous efficiency for ZnCdS NCs-based WLEDs are (0.32, 0.30), 82, 6811 K and 4.26 lm/W, respectively by the UV chip with only one type of ZnCdS NCs layer. The results have exhibited the potential application of ZnCdS NCs as nanophosphors in WLEDs.