Yb^(3+)/Er^(3+)共掺NaYF_4的晶体结构和上转换发光性能的研究  

Crystal Structure and Upconversion Emission of Yb^(3+)/Er^(3+)-Co-Doped NaYF_4 Nanocrystals

作　　者：姚丽丽[1] 罗莉[1] 董国帅[1] 王银海[1] 

机构地区：[1]广东工业大学物理与光电工程学院,广东广州510006

出　　处：《光谱学与光谱分析》2013年第11期2917-2920,共4页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金项目(21271048);广东省自然科学基金项目(07001790)资助

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10mW,980nm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525/550nm附近2 H11/2/4 S3/2→4 I15/2跃迁引起的绿光发射和657nm附近4 F9/2→4 I15/2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2 H9/2→4 I13/2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。Ybs＋/Er3＋-co-doped cubic NaYF4 and Yb3＋/Er~＋/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 pat terns （XRD） and upconversion luminescence spectrum. TEM and XRD results showed that the phase transition from cubic to hexagonal was promoted through Gd3-k 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 under stood. This work focuses analysis of measurement results to compare the effect of crystal phase on the crystal field energy split ting and upconversion emission intensity as well as emission color, and a mechanism of luminescence enhancement and color tun- ability are revealed. Strong visible upconversion luminescence can be seen clearly by the naked eyes in both cubic phase and hexa gonal phase samples upon excitation by a 980 nm laser diode with power of 10 mW, consisting of green emissions centered at a- round 525/550 nm originating from the transitions of 2 Hu/2/4 $3/2→4 Ii5/z and red emission at about 657 nm from 4 Fg/z to 4 Ils/z of Er3＋ ions respectively. In comparison to cubic sample, the hexagonal phase sample presented much stronger and sharper upcon version luminescence, whose emission efficiency was enhanced 10 times with an additional transition of 2 Hg/→4 Ils/z at 557 nm,furthermore, the intensity ratio of red to green emission increased from 2 ： 1 to 3 ： 1. Doping NaYF4 nanocrystals with Gd3＋ i- ons 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 d

关 键 词：稀土 上转换发光 共沉淀法 相变 

分 类 号：O482.3[理学—固体物理]