(Yb3+, Mn2+) Co-doped CdTe nanocrystals with enhanced quantum yields and red-shift emission

We prepared the nanocrystals (NCs) of CdTe, CdTe:Yb, and CdTe:Yb, Mn vis water phase synthesis and examined their structural, morphological, and optical properties. All NCs have a particle diameter of about 2–4 nm, and the monodispersed, uniform spherical, cubic structure of the CdTe NC remains largely unchanged after the doping with Yb and Mn. According to the X-ray diffraction results, the CdTe, CdTe:Yb, and CdTe:Yb, Mn NCs all have a cubic structure, and the diffraction peak of CdTe:Yb NC is at a lower 2θ angle compared with that of the CdTe NC. With the CdTe NC as the reference, the UV–Vis absorption of the CdTe:Yb and the CdTe:Yb, Mn NCs exhibits a blueshift and a redshift, and the emission of CdTe:Yb and CdTe:Yb, Mn has a blueshift of about 12 nm and a redshift of about 73 nm, respectively. The CdTe:Yb, Mn NCs have higher quantum yields than the CdTe:Yb NC, and the quantum yield is the highest when CdTe is doped with 1:1 Mn²⁺/Yb³⁺. In addition, both the CdTe:Yb and CdTe:Yb, Mn NCs have a shorter fluorescence lifetime than the CdTe NC.     

Reduction of Carboxylic Acids by Tetraalkyl Ammonium Borohydride

Tetraalkylammonium borohydride reduces carboxylic acids to the corresponding alcohols in good yields utilizing only stoichiometric quantities of hydride and also in the absence of any Lewis acids.     

Influence of carbon templates and Yb concentration on red and green luminescence of uniform Y2O3:Yb/Er hollow microspheres

Uniform Yb³⁺ and Er³⁺-codoped Y₂O₃ hollow microspheres were synthesized via urea co-precipitation using carbon spheres as templates. Intense red emission (⁴F_9/2→⁴I_15/2) and weak green emission (²H_11/2, ⁴S_3/2→⁴I_15/2) of Er³⁺ were observed for the Yb³⁺ and Er³⁺-codoped Y₂O₃ hollow microspheres under 980 nm infrared excitation. The integrated intensity of visible emission and the ratio of red to green were found to be strongly dependent on the amount of carbon sphere templates and the concentration of Yb³⁺ ions. The amount of carbon sphere templates also plays an important role in adjusting the size of crystallite. Multi-phonon relaxation resulted from the absorbents (OH⁻ and CO₃²⁻) on the surface of the crystallite, and efficient occur of energy transfer processes and cross-relaxation between Er³⁺ and Yb³⁺ are responsible for the enhancement of intensity ratio of red to green emission. Interestingly, for higher concentration of Yb³⁺ ions, the green emission is assigned to a three-phonon process in Y₂O₃:Yb/Er hollow microspheres, which also could result in the increase of the red to green emission ratio. An explanation to account for these behaviors was presented.     

Enhanced photoluminescence of rare-earth doped films prepared by off-axis pulsed laser deposition

Alternate pulsed laser deposition from the host (Al₂O₃) and dopant (Er, Yb) targets has been used to prepare artificially nanostructured films in which the rare earth ion-ion separation is controlled in the nanometer scale in order to control energy transfer between ions. One series of films was prepared in the standard on-axis configuration, i.e. a static substrate being centred with respect to the plasma expansion axis. A second series of films was prepared by rotating the substrate with respect to a shifted axis parallel to the plasma expansion one (off-axis configuration). The latter configuration leads to films with enhanced thickness and Er related photoluminescence intensity uniformity. More interestingly, the Er related photoluminescence lifetime in as-grown films increases up to 2.5 ms, which is much higher than the maximum value of 1 ms obtained for the on-axis configuration films. This enhancement is discussed in terms of a decrease of defect density when using the off-axis configuration.     

不同组分的钒酸盐混晶Ybt:YxGd1-t-xVO4光谱与激光性质的比较研究

研究了三种掺Yb钒酸盐混晶Yb_0.005:Y_0.298Gd_0.697VO₄, Yb_0.007:Y_0.407Gd_0.586VO₄和Yb_0.009:Y_0.575Gd_0.416VO₄的室温偏振吸收谱和发射谱. 结果表明,最强的吸收和发射相应于π偏振,位 关键词： 掺Yb钒酸盐混晶 吸收谱和发射谱 激光振荡 偏振态     

Influence of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu2O3:2%Yb, 0.2%Tm nanopowders

Lutetium oxide nanopowders codoped with Tm³⁺ and Yb³⁺ were synthesized by the reverse-strike co-precipitation method. Effects of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu₂O₃:2%Yb, 0.2%Tm nanopowders had been investigated. The results show that pH value of the precipitant (NH₄HCO₃) solution has a significant effect on the particle size, morphology and upconversion emission intensity of the Lu₂O₃:2%Yb, 0.2%Tm nanopowders. All the samples obtained from different pH value of precipitant solution can be readily indexed to pure cubic phase of Lu₂O₃, indicating good crystallinity. The upconversion emission intensity of Lu₂O₃:2%Yb, 0.2%Tm nanopowders obtained from the precipitant solution with pH=11 is the strongest. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing the number of OH⁻ groups and the enlarged nanopowder size. The strong blue, weak red and near infrared emissions from the prepared nanopowders were observed under 980 nm laser excitation, and attributed to the ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ ion, respectively.     

Yb~(3+)/Er~(3+)掺杂氟氧化物微晶玻璃的制备与发光性能

采用高温熔融法制备了Yb3+/Er3+掺杂的氟氧化物发光微晶玻璃,确定了最佳熔化温度(1 100℃)和退火温度(440℃,480℃)。测定得到基质玻璃的透过率为85%,掺入稀土后,透过率有所下降,并出现了稀土离子的特征吸收峰。980 nm半导体激光器(LD)激发下样品的上转换发射光谱存在4个明显的发射峰,分别为410,532,546和656 nm,对应于2H9/2→4I15/2,2H11/2→4I15/2,4S3/2→4I15/2和4F9/2→4I15/2跃迁。研究了不同Yb3+/Er3+(摩尔分数)和Er3+浓度对上转换发光强度的影响,当Yb3+∶Er3+=4∶1、Er3+摩尔分数为1.5%时,上转换发光强度达到最高。根据发光强度与泵浦功率之间的关系,确定了上转换发射均为双光子过程。讨论了Yb3+,Er3+离子间的能量传递,建立了上转换发光机制。     

An alternative quinoline synthesis by via Friedländer reaction catalyzed by Yb(OTf)3

Quinolines have been synthesized in very good yields from 2-aminoarylketones and differently substituted carbonyl compounds in the presence of Yb(OTf)₃ as the catalyst. The method is applicable to both cyclic and acyclic carbonyl compounds with only slight differences in the experimental procedure.     

六方相NaYF4:Yb/Er纳米晶制备方法研究进展

综述了六方相NaYF4:Yb/Er纳米晶的制备方法,着重总结了三氟乙酸盐热分解法、共沉淀法、碳酸盐热分解法、离子热法、水热法及两步法的研究进展,并就其发展前景进行了展望.     

Synthesis and Infrared Multi‐band Absorption Properties of Core‐shell NaYF4:Yb3+, Er3+@SiO2 Nanoparticles

Due to the unique size effects, nanomaterials in infrared absorption have attracted much attention for their strong absorption in the infrared region. To achieve the infrared multi‐band absorption, we propose to synthesize a core‐shell structure nanomaterial consisting of NaYF₄:Yb³⁺, Er³⁺ core and a layer of SiO₂ as shell. A series of NaYF₄:Yb³⁺, Er³⁺ nanocrystals were synthesized through hydrothermal method by adjusting the ratio of citric acid(CA)‐to‐NaOH, and the effects of CA concentration, and NaOH concentration were studied in detail. NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were synthesized by sol‐gel method using TEOS as silica source. The results show that the core‐shell NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were successfully synthesized. Up‐conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There are no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating are weakened. Furthermore, the property of infrared multi‐band absorption was tested through ultraviolet‐visible‐near infrared spectrophotometer and infrared absorption spectra. The results illustrate that the multi‐band infrared absorption nanomaterial was successfully synthesized.