Synthesis and upconversion luminescence of Lu_2O_3:Yb^(3+),Tm^(3+) nanocrystals

Lutetium oxide nanocrystals codoped with Tm3＋ and Yb3＋ were synthesized by the reverse-like co-precipitation method, using ammonium hydrogen carbonate as precipitant. Effects of the Tm3＋, Yb3＋ molar fractions and calcination temperature on the structural and upconversion luminescent properties of the Lu2O3 nanocrystals were investigated. The XRD results show that all the prepared nanocrystals can be readily indexed to pure cubic phase of Lu2O3 and indicate good crystallinity. The experimental results show that concentration quenching occurs when the mole fraction of Tm3＋ is above 0.2%. The optimal Tm3＋ and Yb3＋ doped molar fractions are 0.2% and 2%, respectively. The strong blue （490 nm） and the weak red （653 nm） emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the 1G4→3H6 and IG4→3F4 transitions of Tm3＋, respectively. Power-dependent study reveals that the 1G4 levels of Tm3＋ can be populated by three-step energy transfer process. The upconversion emission intensities of 490 nm and 653 nm increase gradually with the increase of calcination temperature. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing number of OH- groups and the enlarged nanoerystal size.

Lu_2O_3:Yb^(3+),Tm^(3+)纳米晶的结构和上转换发光性能研究

采用共沉淀法制备了Yb3+和Tm3+共掺杂的Lu2O3纳米晶,用X射线衍射(XRD)、场发射扫描电子显示镜(SEM)和上转换光谱对样品进行了表征。研究了Tm3+浓度和煅烧温度对粉末的结构和上转换发光性能的影响。结果表明,制备出的纳米晶具有纯的Lu2O3相,结晶性较好。在980 nm半导体激光器激发下,样品发射出蓝光、红光和近红外光,并且当Tm3+掺杂摩尔分数超过0.2%时,出现了浓度猝灭效应。随着煅烧温度的增加,纳米晶的尺寸增大,上转换发光强度增强。发射强度与激发功率的关系表明,蓝光490 nm和红光653 nm的发光是三光子过程,近红外811 nm的发光是双光子过程。

Lu_2O_3:Yb^(3+),Tm^(3+)纳米晶的水热法合成和上转换发光性能研究

采用水热法制备了Yb3+和Tm3+共掺杂的Lu2O3纳米晶。研究了前驱体溶液pH对纳米晶的结构、形貌和上转换发光性能的影响。实验结果表明:制备出的纳米晶具有纯的Lu2O3相,结晶性较好。在980nm半导体激光器激发下,样品发射出蓝光和红光,其发光的中心波长分别位于490和653nm。当前驱体溶液pH为9时,Lu2O3:2%Yb3+,0.2%Tm3+纳米晶上转换发光强度最强,这是因为Lu2O3:2%Yb3+,0.2%Tm3+纳米晶的尺寸最大,其表面吸附的OH-基团最少。发射强度与激发功率的关系表明,蓝光490nm和红光653nm的发光是三光子过程。

Energy transfer in Tb^(3+),Yb^(3+) codoped Lu_2O_3 near-infrared downconversion nanophosphors

Tb3＋ and Yb3＋ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3：Tb3＋,Yb3＋ nanophosphors were characterized by X-ray diffraction （XRD） and photoluminescence （PL） spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3＋→Yb3＋ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3＋ （5D4→7F5） and near-infrared （NIR） emission around 973 nm from Yb3＋ （2F5/2→2F7/2） of Lu2O3：Tb3＋,Yb3＋ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3＋ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3＋. The Yb3＋ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3＋ concentration, verifying the efficient energy transfer from the Tb3＋ to the Yb3＋. Cooperative energy transfer （CET） from Tb3＋ to Yb3＋ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3＋ and 2 mol.% Yb3＋, the intensity of NIR emission was the strongest.