The effect of noncoordinating surface ligands with different carbon chain lengths on the optical properties of ZnCdS nanocrystals and their application in white light emitting diodes

• Main Authors: Ya-ching Chen, 陳雅青
• Other Authors: Kuan-wen Wang
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/69619861747061620875

碩士 === 國立中央大學 === 材料科學與工程研究所 === 103 === 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.