Lanthanide-doped LiYF4 nanoparticles: Synthesis and multicolor upconversion tuning

We report the synthesis of tetragonal-phase LiYF₄ nanoparticles doped with upconverting lanthanide ions. The nanoparticles have been characterized by XRD, TEM, and luminescence decay studies. The size of the as-synthesized LiYF₄ nanoparticles can be tuned by varying the precursor ratio of F to lanthanide ions. Passivated by oleic acid ligands, the LiYF₄ nanoparticles can be readily dispersed in a wide range of nonpolar solvents including hexane, cyclohexane, dichloromethane, and toluene. The lanthanide-doped (Yb³⁺, Er³⁺, Tm³⁺, Ho³⁺) LiYF₄ nanoparticles show intense upconversion emissions upon near infrared excitation at 980 nm. By varying composition and concentration of the dopant ions, the color output can be precisely modulated under single wavelength excitation with a diode laser.     

LiYF_4∶Nd~(3+)离子紫外吸收光谱谱带的归属

主要从理论上分析了LiYF4 ∶Nd晶体中Nd3+离子的 4f3→ 4f2 5d跃迁光谱 ,提出了 4f2 5d组态谱项的组合方案 ,从而可以标记 4f2 5d组态的各个能级。据跃迁选律 ,说明了Nd3+离子的基态向 4f2 5d组态的跃迁。理论分析与实验结果符合很好。     

A dibenzofuran-based host material for blue electrophosphorescence

Dibenzofuran (DBF) is converted to a vacuum-sublimable, electron-transporting host material via 2,8-substitution with diphenylphosphine oxide moieties. Close pi-pi stacking and the inductive influence of P=O moieties impart favorable electron-transport properties without lowering the triplet energy. A maximum external quantum efficiency of 10.1% and luminance power efficiency of 25.9 lm/W are realized using this material as the host for the blue-green electrophosphorescent molecule, iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C(2')picolinate (FIrpic).     

Theory of radiationless transitions in a crystalline host material

Consistent calculations of the rate constant of radiationless electron transition are reported for a diatomic molecule in a crystal at zero temperature. The transition between electronic states occurs due to nonadiabaticity. Relaxation of the vibrational energy is stimulated by the interaction of the molecule with the crystal. The calculations have been carried out under the assumption that perturbation theory with respect to the nonadiabaticity operator is applicable. The vibrational interaction of the molecule with the environment is assumed not to be small. The electronic terms of the molecule are approximated by Morse potentials.     

Investigations of the EPR parameters for Sm3+ ions in KY3F10 and LiYF4 crystals

In this paper, we calculate the EPR parameters (g factors g parallel, g perpendicular and hyperfine structure constants A parallel, A perpendicular) of rare earth ion Sm3+ in fluoride crystals KY3F10 and LiYF4 from the perturbation formulas of EPR parameters for a 4f5 ion in tetragonal symmetry. In these formulas, the crystal-field J-mixing of the first and second excited-state multiplets 6H(7/2) and 6H(9/2) into the ground state multiplet 6H(5/2), the mixtures among the states with the same J value via spin-orbit coupling interaction and the interactions between the ground Kramers doublet Gammagamma and the same irreducible representation as Gammagamma in other 11 Kramers doublets Gammax within 6HJ (J=5/2, 7/2, 9/2) states via crystal-field and orbital angular momentum (or hyperfine structure) are considered. The calculated results (which are in agreement with the observed values) are discussed.     

Photostability of the laser dye DCM in various inorganic-organic host matrices

The laser dye, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) was incorporated in various inorganic-organic host matrices by the sol-gel technique. The photostability of the DCM-doped materials under CW argon laser irradiation was investigated. The absorption of DCM monomer ar 480 nm decreased with increasing irradiation time and was accompanied by an increase in the absorption at 352 nm by inactive photoproducts. Photostability was estimated by measuring the decay rates of DCM fluorescences in different host matrices. The rates exhibited two components; a rapid decay within the first several tens of seconds followed by a slower luminescence decay. The rapid decay depended upon the DCM content in the matrix while the slow decay component was related to the mobility of the DCM in the different matrices. The silica host matrix containing phenyl and a small amount of epoxy groups exhibited the best photostability of the materials examined.     

亚晶格能量团簇构建及晶场调控对四方LiYF4:RE上转换发光机制的影响研究

四方LiYF₄是一种与六方NaYF₄相当的稀土上转换发光基质材料,由于相对优异的短波上转换发光特性,近年受到业界的相当关注,但对产生这一优异特性的原因还未见报道.经研究发现,四方LiYF₄具有六边环状亚晶格结构,每5个间距小于0.4 nm的近邻三价阳离子形成一个团簇,稀土离子间的能量传递容易在团簇内或六边形环内环绕传递.基于它的这一亚晶格结构特征,本工作通过引入不同量敏化剂Yb³⁺和掺杂离子Sc³⁺和Hf⁴⁺,考察不同激活离子Er³⁺、Ho³⁺和Tm³⁺与敏化离子Yb³⁺构建亚晶格能量团簇以及异质离子Sc³⁺和Hf⁴⁺掺杂晶场调控对稀土离子上转换发光性能的影响机制.发现不同稀土离子与Yb³⁺存在不同的能级匹配,导致不同概率的无辐射交叉弛豫行为,当引入适量的Yb³⁺时,可分别构建1Er-2Yb、1Ho-2Yb和1Tm-4Yb亚晶格能量团簇,实现最佳的上转换发光性能;当6 mol% Sc³⁺和4 mol% Hf⁴⁺引入时,可有效调控晶场的不对称性;掺杂后,5个近邻三价离子的团簇结构中,只有3个近邻Yb³⁺离子,无法同时实现Er³⁺离子的⁴F_5/2和Sc³⁺的²G_7/2或Hf⁴⁺的⁴F_5/2^o激发态的双光子合作上转换电子布居,导致Sc³⁺或Hf⁴⁺成为荧光猝灭中心,Sc³⁺掺杂晶场调控最大仅提升50%的荧光强度,Hf⁴⁺掺杂没有提升反而降低Er³⁺离子的上转换发光强度,不同于它们掺杂六方NaYF₄：Er/Yb那样扮演储能离子角色,显著提升Er³⁺离子的短波上转换发光强度.本研究揭示了在六边环状亚晶格基质结构中不同稀土离子与敏化剂Yb³⁺的敏化上转换发光机制,以及基质结构特征对掺杂晶场调控行为的影响机制,可为设计和制备高性能上转换发光材料提供借鉴.     

Synthesis of dibenzothiophene-containing ladder polysilsesquioxane as a blue phosphorescent host material

A ladder polysilsesquioxanes with side chain of dibenzothiophene groups (BS-LPSQ) was successfully synthesized. The ladder structure of BS-LPSQ was characterized by MALDI-TOF MS, XRD, and (1)H?NMR spectroscopy. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), atomic force microscopy (AFM), and spectroscopic analyses revealed that the BS-LPSQ has good film-forming ability, high thermal and morphological stability, and good miscibility to the dopant iridium bis(4,6-difluorophenyl)pyridinato-N,C(2)-picolinate (FIrpic), high triplet energy, and a wide bandgap. In addition, compared with the ringed polysiloxane BS-PSQ phosphorescent host material reported previously, the ladder structure of BS-LPSQ has not only a higher thermal resistance, but also could prevent molecular aggregation and effectively avoid quenching of fluorescence. Thus, the BS-LPSQ may be used as a better host for the blue-light-emitting iridium complex FIrpic. The performance of the electrophosphorescent device, based on the ladder BS-LPSQ as the active layer, is superior to that of ringed BS-PSQ and any other polyhedral oligomeric silsesquioxane (POSS)-based or polymer host materials.     

Role of the support material on laser desorption/ionization mass spectra

We report the results of experimental studies on the effects of sample supports in laser desorption/ionization mass spectrometry (LDI-MS). LDI time-of-flight (TOF) mass spectra obtained for C(60) and insulin samples deposited onto standard stainless steel substrate and/or onto some non-metallic materials (glass, scotch tape, floppy disc foil, Teflon foil, photocopy film), all recorded under identical, typical experimental conditions, have been compared with regard to their intensity and quality. The LDI investigations show that compared with stainless steel, glass and floppy disc foil sample supports boost (2-3.5 times) ion yields for C(60)(+) and C(60)(-) ions, respectively. The stainless steel and scotch tape sample supports are the best for the mass resolution of positive ions and the formation of (C(60))(n)(-) (n 相似文献   

N-苯甲酰基-N'-4-甲基苯基硫脲的结构研究

硫脲及其衍生物由于其广泛的应用已引起了人们的重视。本文报道N-苯甲酰基-N’-4-甲基苯基硫脲的单晶结构。并用密度泛函(DFT)理论的B3LYP杂化函数方法对所选的分子进行相应的构型优化和分析。