光谱学与光谱分析, 2013, 33 (11): 2917, 网络出版: 2013-11-14  

Yb3+/Er3+共掺NaYF4的晶体结构和上转换发光性能的研究

Crystal Structure and Upconversion Emission of Yb3+/Er3+-Co-Doped NaYF4 Nanocrystals
作者单位
广东工业大学物理与光电工程学院, 广东 广州510006
摘要
以乙二胺四乙酸(EDTA)为螯合剂, 用一种改进的共沉淀法制备了Yb3+/Er3+共掺的立方相NaYF4和Yb3+/Er3+/Gd3+三掺的六角相NaYF4纳米晶。 用透射电子显微镜、 X射线衍射、 荧光光谱等测量手段对样品的形貌、 晶相和发光性能进行了表征。 结果表明, 通过掺杂Gd3+, 实现了NaYF4基质从立方相到六角相的相变。 虽然据报道六角相的NaYF4比立方相的NaYF4上转换效率高, 但是相变对上转换荧光光谱的影响还不清楚。 本文着重研究了相变对晶格场能级分裂、 发光强度和发光颜色的调控作用, 提出了荧光增强和发光颜色可调的机理。 用10 mW, 980 nm二极管激光激发, 在立方相和六角相样品中均观察到肉眼可见的上转换荧光发射, 分别是525/550 nm附近2H11/2/4S3/2→4I15/2跃迁引起的绿光发射和657 nm附近4F9/2→4I15/2跃迁引起的红光发射。 与立方相样品相比, 六角相样品荧光发射谱线变窄, 荧光强度增强了一个量级, 出现了2H9/2→4I13/2跃迁引起的新发射峰, 红绿比由2∶1增大到3∶1, 这是因为六角相基质的晶格场对称性降低, 于是增强了上转换荧光强度, 同时六角相的晶胞体积变小, 提高了掺杂离子周围的晶格场强度, 导致发射谱线变锐, 表明相变可以调节晶格场能级分裂, 发光强度和发光颜色。
Abstract
Yb3+/Er3+-co-doped cubic NaYF4 and Yb3+/Er3+/Gd3+-tri-doped hexagonal NaYF4 nanocrystals were synthesized by a modified coprecipitation method with ethylenediamine tetraacetic acid (EDTA) as chelating agent. The samples’ morphology, crystal phase and upconversion emission were measured with transmission electron microscope (TEM), X-ray diffraction patterns (XRD) and upconversion luminescence spectrum. TEM and XRD results showed that the phase transition from cubic to hexagonal was promoted through Gd3+ doping. It has been reported that the upconversion efficiency of hexagonal NaYF4 is higher than that of cubic NaYF4, however, the effect of crystal phase on upconversion luminescence has not been well understood. This work focuses analysis of measurement results to compare the effect of crystal phase on the crystal field energy splitting and upconversion emission intensity as well as emission color, and a mechanism of luminescence enhancement and color tunability are revealed. Strong visible upconversion luminescence can be seen clearly by the naked eyes in both cubic phase and hexagonal phase samples upon excitation by a 980 nm laser diode with power of 10 mW, consisting of green emissions centered at around 525/550 nm originating from the transitions of 2H11/2/4S3/2→4I15/2 and red emission at about 657 nm from 4F9/2 to 4I15/2 of Er3+ ions respectively. In comparison to cubic sample, the hexagonal phase sample presented much stronger and sharper upconversion luminescence, whose emission efficiency was enhanced 10 times with an additional transition of 2H9/2→4I13/2 at 557 nm, furthermore, the intensity ratio of red to green emission increased from 2∶1 to 3∶1. Doping NaYF4 nanocrystals with Gd3+ ions induced the hexagonal-to-cubic phase transition and thus decreased the crystal symmetry, consequently increased absorption cross-section and 4f—4f transition probabilities by relaxing forbidden selection rules, resulting in stronger emission. In the mean time, the decreasing unit-cell volume of the hexagonal phase increased the crystal field strength around the dopant ions and consequently led to that hexagonal phase samples present much sharper emission compared to cubic counterparts. It demonstrates that phase transition can tune crystal field energy splitting, luminescence intensity and emission color.

姚丽丽, 罗莉, 董国帅, 王银海. Yb3+/Er3+共掺NaYF4的晶体结构和上转换发光性能的研究[J]. 光谱学与光谱分析, 2013, 33(11): 2917. YAO Li-li, LUO Li, DONG Guo-shuai, WANG Yin-hai. Crystal Structure and Upconversion Emission of Yb3+/Er3+-Co-Doped NaYF4 Nanocrystals[J]. Spectroscopy and Spectral Analysis, 2013, 33(11): 2917.

关于本站 Cookie 的使用提示

中国光学期刊网使用基于 cookie 的技术来更好地为您提供各项服务,点击此处了解我们的隐私策略。 如您需继续使用本网站,请您授权我们使用本地 cookie 来保存部分信息。
全站搜索
您最值得信赖的光电行业旗舰网络服务平台!