摘要
为了解决碳点(CDs)在固态或聚集状态下荧光猝灭问题,提出了一种基于无机物复合的碳点固态荧光策略。以柠檬酸和乙醇胺为原料合成的青光碳点溶液(C-CDs)及水稳定性良好的氟铋钾(K0.3Bi0.7F2.4)为基质,在室温下通过共沉淀法复合制备C-CDs@K0.3Bi0.7F2.4纳米复合材料。通过XRD、TEM、FT-IR和XPS等表征手段,证明了C-CDs附着在K0.3Bi0.7F2.4纳米粒子上。此外,还研究了C-CDs@K0.3Bi0.7F2.4纳米复合材料热稳定性能。结果表明,C-CDs@K0.3Bi0.7F2.4纳米复合材料不仅能够在波长450 nm激发下发射出555 nm黄色荧光,而且在125 ℃下还能保持初始强度的55%,说明共价键复合的C-CDs@K0.3Bi0.7F2.4纳米复合材料具有较好的热稳定性。该研究不仅为CDs基荧光粉的制备提供了一种新方法,也展现了CDs在照明领域中的应用前景。
碳点(Carbon dots, CDs)作为一种最有前途的碳基纳米材料,其具有优异的发光性
柠檬酸(CA,99.5%)购买于阿拉丁公司(中国上海),乙醇胺(EA,99%)购买于麦克林公司(中国上海)。分析级的五水硝酸铋Bi(NO3)3·5H2O(99%)和氟化钾(KF)试剂购自阿拉丁公司(中国上海),乙二醇(EG)是从北京化学试剂公司获得,氟化铵(NH4F,98%)产自国药化学试剂有限公司。所有的化学品都是直接使用的,没有进一步的纯化。
将0.630 4 g的柠檬酸溶于30 mL的去离子水中,然后加入3.621 mL的乙醇胺,密封,在50 mL的特氟龙内衬不锈钢高压釜中经8 h加热至160 ℃,待反应结束后冷却至室温。将所得产物转移到离心管中,以10 000 r·mi
首先将1 mmol的Bi(NO3)3·5H2O、1 mmol的KF与10 mL的EG混合,待完全溶解后加入1 mL浓度为0.09 g·

图1 C-CDs@K0.3Bi0.7F2.4纳米复合材料的合成示意图
Figure 1 Schematic diagram of the synthesis of C-CDs@K0.3Bi0.7F2.4 composites
所有样品的XRD测量在粉末衍射仪(X´Pert PRO,Cu Kα,λ=1.5418 Å)上进行,用扫描电子显微镜(SEM,JSM-6700F)对样品的形貌进行表征。使用JEOL JEM 2100记录透射电镜(TEM)和高分辨率透射电镜(HRTEM)对样品的漫反射(DR)进行测量,用紫外-可见-近红外分光光度计(Lambda 950, Perkin Elmer)测量样品的吸收光谱,以BaSO4为标准参比。利用Aicolex Nexus 470型红外光谱仪,通过混合样品与片剂KBr获得红外光谱。以450 W氙灯为光源,在爱丁堡仪器公司生产的FLS980荧光光谱仪上对样品进行稳态和动态光谱分析。对于温度相关的样品的发射测量,在Linkam THMS600冷热台上进行温度控制加热。X射线光电子能谱(XPS)在Thermo Scientific K-Alpha上进行分析。

图2 C-CDs和C-CDs@K0.3Bi0.7F2.4的光学性能图
Figure 2 Optical properties of C-CDs and C-CDs@K0.3Bi0.7F2.4

图3 K0.3Bi0.7F2.4和C-CDs@K0.3Bi0.7F2.4的XRD图
Figure 3 XRD patterns of K0.3Bi0.7F2.4 and C-CDs@K0.3Bi0.7F2.4
为了进一步研究C-CDs@K0.3Bi0.7F2.4纳米复合材料的微观形貌,首先对合成的C-CDs进行了形貌结构表征,

图4 C-CDs的TEM和HRTEM图
Figure 4 TEM and HRTEM of C-CDs
其次,对K0.3Bi0.7F2.4和C-CDs@K0.3Bi0.7F2.4纳米复合材料的形貌进行了表征,

图5 K0.3Bi0.7F2.4及C-CDs@K0.3Bi0.7F2.4的SEM图和HRTEM图
Figure 5 SEM image and HRTEM image of K0.3Bi0.7F2.4 and C-CDs@K0.3Bi0.7F2.4

图6 C-CDs@ K0.3Bi0.7F2.4元素分布图
Figure 6 EDS element distribution of C-CDs@K0.3Bi0.7F2.4
为了探究C-CDs@K0.3Bi0.7F2.4纳米复合材料的元素组成和化学结构,对其进行了FT-IR和XPS的表征。

图7 C-CDs、K0.3Bi0.7F2.4和C-CDs@K0.3Bi0.7F2.4的FT-IR、XPS光谱图
Figure 7 The FT-IR spectra and XPS survey spectra of C-CDs,K0.3Bi0.7F2.4 and C-CDs@K0.3Bi0.7F2.4
从紫外吸收光谱可知C-CDs 在300—400 nm 的宽吸收带归属于C═O键,并且吸收带位置与C-CDs溶液位于420 nm的宽激发峰(350—450 nm) 部分重合。综合上述结果与分析,C-CDs的发光主要来自于表面态发
荧光粉在高温下的发光稳定性,通常被认为是评价其应用潜力的重要标准。基于上述分析,进一步测量了在λex=450 nm激发下C-CDs@K0.3Bi0.7F2.4纳米复合材料的热稳定性,结果如

图8 不同温度下C-CDs@K0.3Bi0.7F2.4纳米复合材料的热稳定性
Figure 8 Thermal stability of C-CDs@K0.3Bi0.7F2.4 nanocomposites at different temperatures
采用一种简单快速的共沉淀方法,制备出了基于C-CDs的长波长固态发光材料,C-CDs@K0.3Bi0.7F2.4为发射波长位于555 nm的黄色荧光纳米复合材料,其可有效抑制C-CDs的聚集诱导荧光猝灭。C-CDs@K0.3Bi0.7F2.4的发射波长与C-CDs溶液波长相比发生了红移,红移的原因是引入B
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