【作者】 赵永强；

【导师】 刘旭光；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2015， 硕士

【摘要】 发光二极管（LED）具有能耗低、光效高以及寿命长等优点，近年来受到科学界和产业界的广泛关注。实际应用中，以单一基质白光荧光粉的研究最为关键。白光LED用荧光粉分为稀土基荧光粉、胶体量子点荧光粉以及碳点（Carbon dots，CDs）荧光粉三大类。其中，CDs由于具有荧光量子产率高、稳定性高及毒性低等优点，成为近年来发光材料研究的热点。为了提高白光LED用CDs荧光粉的荧光量子产率和蓝、绿、红光总比重，本论文以一水合柠檬酸为碳源，分别以乙二胺、硫脲和L-半胱氨酸为添加剂，在不同温度下水热反应6h，制得氮掺杂碳点（Nitrogen-doped CDs,N-CDs）与氮硫掺杂碳点（Nitrogen and sulphur-doped CDs, NS-CDs），并对其进行结构和光学性质分析。优选荧光量子产率最高且蓝、绿、红光总比重较高的产物N-CDs4和NS-CDs9，并以其为荧光粉制作了白光LED，对白光LED的色坐标和相关色温（Correlated color temperature, CCT）进行了表征。通过研究，得到以下结论：(1) N-CDs的制备与性质。随着乙二胺添加量的增加，N-CDs的荧光量子产率先增高、后降低。在160-200℃内，其荧光量子产率基本不随反应温度的变化而变化。乙二胺添加量和反应温度基本不影响N-CDs的光谱组成。当一水合柠檬酸与乙二胺摩尔比为1:4，反应温度为200℃时，得到最优N-CDs4，其荧光量子产率为67.06%；在光谱中，红、绿、蓝光总比重为53.01%，均高于目前文献所报道的最高值。具有两个荧光中心，寿命为17.0ns的荧光中心向寿命为11.1ns的荧光中心发生了能量转移。C-N基团的引入能够提高N-CDs的荧光量子产率。(2) NS-CDs的制备与性质。随着硫脲添加量的增加，含C=S官能团NS-CDs的荧光量子产率先增高、后降低；在160-200℃内，该NS-CDs的荧光量子产率随反应温度的升高而增加；蓝、绿、红光总比重随硫脲添加量和反应温度的增加而降低。当一水合柠檬酸与硫脲摩尔比为1:1，反应温度为200℃时，得到最优NS-CDs3。其荧光量子产率为9.80%；在光谱中，红、绿、蓝光总比重为47.82%；平均荧光寿命为8.88ns；其荧光衰减曲线符合三指数函数，意味着NS-CDs3有三个荧光中心。而含有C-S官能团的NS-CDs9的荧光量子产率高达65.37%，红、绿、蓝光总比重高达61.93%。较C-S官能团，C=S官能团不利于CDs荧光量子产率的提高。S元素的引入能够有效提高NS-CDs的蓝、绿、红光总比重。(3)白光LED的制备与光学性能。采用具有最高荧光量子产率和较高蓝、绿、红光总比重的N-CDs4和NS-CDs9作为荧光粉制备了白光LED。N-CDs4基白光LED色坐标为（0.38，0.42），CCT为4290K。NS-CDs9基白光LED色坐标为（0.32,0.36），CCT为5822K。光学密封胶和聚乙烯醇水凝胶使CDs发射光谱产生明显红移，全部覆盖可见光区。实现LED直接发射白光。更多还原

【Abstract】 Light emitting diode (LED) has attracted great attention from scientific andindustrial community owing to low energy consumption, high efficiency andlong lifetime. Research on single-phase phosphor for white LED is scientificallyand industrially significant. Single-phase phosphor for white LED is based onrare earth, colloidal quantum dots, and carbon dots (CDs). CDs have becomehotspots of single-phase phosphor owing to high quantum yield and stability aswell as low toxicity.In order to enhance quantum yield (QY) and blue-to-red light emitting,single-phase CDs phosphor was hydrothermally prepared for6h at variousreaction temperatures using citric acid monohydrate as carbon source,ethylenediamine, thiourea and L-cysteine as additives, obtaining nitrogen-dopedCDs (N-CDs) and nitrogen and sulphur-doped CDs (NS-CDs). OptimizedN-CDs4and NS-CDs9with highest QY and blue-to-red light emitting wereselected to fabricate white LEDs. Chromaticity coordinate and correlated colortemperature (CCT) of white LEDs were characterized.The results are as follows:(1) Preparation and characterization of N-CDs. QY of N-CDs increasedinitially and declined thereafter with increasing ethylenediamine addition. In160-200℃, QY of N-CDs exhibited temperature-independent behavior.Blue-to-red light emitting of N-CDs was independent of ethylenediamineaddition and reaction temperature. N-CDs with the highest QY (i.e., N-CDs4) were obtained with molar ratio of citric acid to ethylenediamine1:4and reactiontemperature200℃. QY and blue-to-red light emitting of N-CDs4was67.06%and53.01%, respectively, which were higher than those reported by others. Twofluorescence centers were discovered in N-CDs with lifetime17.0ns and11.1ns,separately. Energy transfer was measured from fluorescence center with lifetime17.0ns to that with lifetime11.1ns. QY of N-CDs was promoted owing tointroduction of C-N group.(2) Preparation and characterization of NS-CDs. QY of NS-CDs with C=Ssurface group increased initially and decreased subsequently with increasingthiourea addition. In160-200℃, QY of NS-CDs with C=S surface group isproportional to increasing temperature. Blue-to-red light emitting of NS-CDswith C=S surface group is inversely proportional to increasing thiourea additionand reaction temperature. NS-CDs with the highest QY (i.e., NS-CDs3) wereobtained with molar ratio of citric acid to thiourea1:1and reaction temperature200℃. QY and blue-to-red light emitting of NS-CDs3was9.80%and47.82%,respectively. With the average fluorescence lifetime8.88ns, NS-CDs exhibitedthree fluorescence centers. The lifetime of CDs was delivered by fitting thedecay traces with a triexponential functional model. QY and blue-to-red lightemitting of NS-CDs9with C-S surface group was65.37%and61.93%,respectively, indicating that C=S surface group antagonized promotion of QYcompared with C-S surface group. Blue-to-red light emitting of NS-CDs wasefficiently boosted by introduction of sulfur.(3) Fabrication and optical properties of CDs-based white LED. N-CDs4andNS-CDs9were employed as single-phase phosphor. Chromaticity coordinateand CCT of white LED based on N-CDs4were (0.38,0.42) and4290K,respectively. Chromaticity coordinate and CCT of white LED based onNS-CDs9were (0.32,0.36) and5822K, respectively. Red shift of CDs emission spectra was discovered owing to optical encapsulant and polyvinyl alcoholhydrogel, leading to emission covering the entire visible range and direct whiteLED.更多还原