共沉淀法制备NaYF4 : Tm3+,Yb3+的上转换发光

通过共沉淀法制备Tm³⁺和Yb³⁺掺杂的NaYF₄上转换发光材料。其中Tm³⁺和Yb³⁺的摩尔分数分别为0.01%,0.1%。在室温下测试了NaYF₄ : Tm³⁺,Yb³⁺材料在300~1 100 nm的吸收光谱。利用X射线衍射(XRD),扫描电镜(SEM)测试了合成材料的物相结构和微观形貌。结果表明:NaYF₄ : Tm³⁺,Yb³⁺材料为六方相晶体,其颗粒大小约为50~60 nm,产物结晶良好,含有少量杂相。在798 nm近红外光激发下,测试了样品的上转换发光光谱。观察到了蓝、绿色上转换发光。讨论了上转换发光的可能机理,蓝光主要来源于Tm³⁺的激发态¹G₄到基态³H₆的跃迁,绿光来源于Tm³⁺的¹D₂→³H₅跃迁。

Upconversion Luminescence Properties of NaYF4:Tm3+, Yb3+Synthesized by Co-precipitation Method

The upconversion (UC) processes of infrared light to visible light of rare earth ions doped different hosts have been investigated extensively, due to their potential applications in some fields, such as solid-state lasers, display, communications, and so on. The recent researches emerging at the intersection of nanotech-nology and biotechnology are opening up a new period for the development of UC. As known, the controlled fabrication of a host with aimed structure is important for enhancing the upconversion efficiency, because the phonon energy of the host can affect the probabilities of non-radiative decay and the energy transfer. Therefore, it is necessary to choose a lattice with much lower phonon energy, which is benefit to the upconversion luminescence. Rare earth-doped hexagonal sodium yttrium fluoride (NaYF₄) is a good host, which is known to be a very efficient near-infrared to visible upconverter. The hexagonal NaYF₄ has low phonon energy. The structure of hexagonal phase gives rise to controversy about the cation sites and distribution. The trivalent thulium (Tm³⁺) is an ideal candidate for single wavelength NIR upconversion due to its ladder of nearly equally spaced energy levels that are multiples of the ¹G₄→³H₆ transition. The development of compact blue lasers based on Tm³⁺ upconversion processes is nowadays widely studied mainly due to the potential of high perfor-mance OEM applications, such as biomedical and analytical instrumentation, display, photoprinting. In thu-lium doped media, the efficiency of this process is very low, but it was noticed that the mechanism could be made one or two orders of magnitude more efficient by using ytterbium(Yb³⁺). In this paper, trivalent thu-lium (Tm³⁺) and yttebium (Yb³⁺) ions codoped NaYF₄ were synthesized by co-precipitation method. The concentration of Tm³⁺ and Yb³⁺ are 0.01%, 0.1%, respectively. The absorption spectrum of NaYF₄∶Tm³⁺,Yb³⁺ from 300 to 1 100 nm was measured at room temperature. The upconversion emission was observed when excited by 798 nm. The green and blue upconversion emission spectra were measured. Based on the experimental results the possible upconversion mechanism was analyzed. The main mechanism is the in-direct sensitization of Tm³⁺ and Yb³⁺. The blue emitting light results from the transition of ¹G₄→³H₆ of Tm³⁺, green emitting light is from the transition of ¹D₂ →³F₄ of Tm³⁺. To our knowledge, there have not been similar works published domestically and abroad. The structural properties of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that NaYF₄∶Tm³⁺, Yb³⁺ prepared by co-precipitation method exhibits hexagonal crystal phase.