K_2YF_5∶Tm^(3+)单晶的光谱和能级结构

在12K的温度下,测量了水热法生长的K2YF5∶Tm3+单晶的发射和吸收光谱,分析了高掺杂样品中Tm3+离子间的交叉弛豫行为。用最小二乘法对实验能级进行拟合计算,得到了较好的均方差:18cm-1。此外,文中还给出了K2YF5∶Tm3+共振激发下1D2和1G4能级寿命的测量结果,并分析和讨论了掺杂量对能级寿命的影响。

2-硝基-2-苄基-1,3-丙二醇的合成

2-硝基-2-苄基-1,3-丙二醇是合成药物中间体α-丝氨酸的重要先行体,它由β-硝基苯乙烷与三聚甲醛在碱催化条件下的羟醛缩合反应合成。产物通过重结晶得到无色透明晶体,产率49.01%。对去质子剂、反应物配料比、反应温度以及反应时间进行了优化。产物的结构通过1 H NMR,13CNMR,IR表征。X-Ray单晶衍射分析揭示分子间和分子内氢键的存在。

Sum Frequency Generation Vibrational Spectra of Perovskite Nanocrystals at the Single-Nanocrystal and Ensemble Levels

Determination of molecular structures of organicinorganic hybrid perovskite(OIHP)nanocrystals at the single-nanocrystal and ensemble levels is essential to understanding the mechanisms responsible for their size-dependent optoelectronic properties and the nanocrystal assembling process,but its detection is still a bit challenging.In this study,we demonstrate that femtosecond sum frequency generation(SFG)vibrational spectroscopy can provide a highly sensitive tool for probing the molecular structures of nanocrystals with a size comparable to the Bohr diameter(∼10 nm)at the single-nanocrystal level.The SFG signals are monitored using the spectral features of the phenyl group in(RMBA)PbBr_(3) and(R-MBA)_(2)PbI_(4) nanocrystals(MBA:methyl-benzyl-ammonium).It is found that the SFG spectra exhibit a strong resonant peak at 3067±3 cm^(−1)(ν2 mode)and a weak shoulder peak at 3045±4 cm^(−1)(ν_(7a) mode)at the ensemble level,whereas a peak of theν2 mode and a peak at 3025±3 cm^(−1)(ν20b mode)at the single-nanocrystal level.The nanocrystals at the single-nanocrystal level tend to lie down on the surface,but stand up as the ensemble number and the averaged sizes increase.This finding may provide valuable information on the structural origins for size-dependent photo-physical properties and photoluminescence blinking dynamics in nanocrystals.

Signatures for Coexistence of Monoclinic and Hexagonal Phases in GaTe Nanoflakes

The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.

Optical Absorption and Refractive Index Study of Ti： Al2O3 Single Crystal

The optical absorption of Ti：Al2O3 single crystal has been measured at room temperature, in the wavelength region between 200 nm and 800 nm. The main absorption peaks at 491 nm and 562 nm, the weak infrared absorption band with a peak at 650 nm and the strong UV absorption band below 300 nm were observed. The refractive index is discussed by using Fresnel＇s equation. In particular, the Sellmeier equation was determined in the visible region by means on non-conventional method based on the measurement of refraction by using UV-visible spectroscopy. The refractive indices decreased from 3.71 to 1.28 with wavelength in the range 400-800 nm.

Band structure reconstruction across nematic order in high quality FeSe single crystal as revealed by optical spectroscopy study

We perform an in-plane optical spectroscopy measurement on high quality FeSe single crystals grown by a vapor transport technique. Below the structural transition at Ts - 90 K, the reflectivity spectrum clearly shows a gradual suppression around 400 cm-1 and the conductivity spectrum shows a peak at higher frequency. The energy scale of this gap-like feature is comparable to the width of the band splitting observed by ARPES. The low-frequency conductivity consists of two Drude components and the overall plasma frequency is smaller than that of the FeAs based compounds, suggesting a lower cartier density or stronger correlation effect. The plasma frequency becomes even smaller below Ts which agrees with the very small Fermi energy estimated by other experiments. Similar to iron pnictides, a clear temperature-induced spectral weight transfer is observed for FeSe, being indicative of strong correlation effect.

Mssbauer spectroscopic study of Fe-Mg tourmalines with different Fe contents

We studied four tourmalines with different Fe contents from Xinjiang,Sichuan,and Yunnan provinces of China using Mossbauer spectroscopy and single crystal X-ray diffraction.The valence and location of Fe in the four tourmalines and two heat-treated tourmalines have been investigated.The experimental results showed that Fe in the four tourmalines at room temperature had two valence states and two locations,i.e.Fe2＋（Y）,Fe2＋（Z）,Fe3＋（Y）.After being heated at 850℃ for 48 and 72 h,Fe elements in tourmaline were nearly completely oxidized and mainly occupied Y sites,and a small amount of Fe3＋ shifted to Z sites.Simultaneously,the amount of mixed valence state Fe 2.5＋ progressively increased with heating time,and electron delocalization occurred between the adjacent sites [Fe2＋-Fe3＋].

Putting aniline radical cations in a bottle

Salts containing aniline radical cations have been isolated and characterized by electron paramagnetic resonance(EPR)spectroscopy, UV-Vis absorption spectroscopy and single crystal X-ray diffraction. The EPR spectra and theoretical calculations indicate the unpaired electron is delocalized on phenyl rings and nitrogen atoms. Both radical cations feature a quinoidal geometry with a partially double C–N bond, but are distinct in that the C–N bond is coplanar to the phenyl plane in one cation while deviates from the plane in the other due to steric crowding. The work provides the first unequivocal examples of stable aniline radical cations.

An inverted triplesalen ligand by a convergent synthesis and its influence on trinuclear Fe_3~Ⅲ complexes

The inverted triplesalen ligand H6feldMe has been synthesized from 2,4,6-triformyl-phloroglucinol and a ketimine salen half-unit in a convergent synthesis. NMR, IR, and UV-vis spectroscopy reveal that this ligand is not in the O-protonated tau- tomer but in the N-protonated tautomer with substantial heteroradialene contribution. This ligand and the conventional triple- salen ligand H6talent-au2 have been used to synthesize the trinuclear Fem complexes [（feldMe）（FeCl）3] and [（talent-Bu2）（FeC1）3], respectively. The molecular structures of these complexes were obtained by single-crystal X-ray diffraction. Two trinuclear Fem complexes of [（feldMe）（FeCl）3] dimerize via two Fe-phenolate bonds, whereas due to steric hindrance no dimerization is observed for [（talent-Bu2）（FeC1）3]. The structural data also reveal some heteroradialene contribution in the trinuclear complexes. Whereas UV-vis and MOlSbauer spectroscopy are not suitable to distinguish between the two complexes, FT-IR spectra show characteristic features due to the different substitution patterns of the conventional and the inverted triplesalen ligands. Another handle is provided by electrochemistry. Whereas both complexes exhibit an irreversible oxidation wave （0.94 V vs. Fc＋/Fc for [（feldMe）（FeC1）3] and 0.84 V vs. Fc~/Fc for [（talent-Bu2）（FeC1）3]）, which is assigned to the oxidation of the central backbone, higher potential oxidations are reversible for [（talent-Bu2）（FeC1）3]） but irreversible for [（feldMe）（FeC1）3]. This is attributed to the reversible oxidation of the terminal phenolates in the di-tert-butyl substituted [（talentBu2）（FeCl）3] in contrast to the mono-methyl-substituted phenolates in [（feld^ae）（FeC1）3]. The magnetic properties of [（talen^-Bu2）（FeC1）3] reveal a very small ferromagnetic coupling with significant zero-field splitting of the Feul S = 5/2 ions. In contrast, the dimerization of two trinu- clear complexes in [（feldMe）（FeCl）3] results in antiferromagnetic interactions between the two phenolate-bridged FeIII ions, which mask the intra-trinuclear interactions transmitted by the central phloroglucinol backbone.

Fabrication of single-crystalline ZnSe multipod-based structures

ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group's semiconductor materials with controllable morphologies.

The optical properties of Tm^(3+) doped Na_5Lu_9F_(32) single crystal

Tm^(3+) doped Na_5Lu_9F_(32) single crystal with high optical quality was grown by an improved Bridgman method. The Judd-Ofelt intensity parameters ?_t(t=2, 4, 6) were calculated according to the measured absorption spectra and physical-chemical properties of the obtained Na_5Lu_9F_(32) single crystal. The stimulated emission cross-section of the ~3F_4→~3H_6 transition(～1.8 μm) is 0.35×10^(-20) cm^2 for Tm^(3+) doped Na_5Lu_9F_(32) single crystal. The emission spectra under the excitation of 790 nm laser diode(LD) and fluorescence lifetime at 1.8 μm were measured to reveal the fluorescence properties of Tm^(3+) doped Na_5Lu_9F_(32) single crystal. The research results show that the Tm^(3+) doped Na_5Lu_9F_(32) single crystal has larger stimulated emission cross-section compared with other crystals. All these spectral properties suggest that this kind of Tm^(3+)doped Na_5Lu_9F_(32) crystal with high physical-chemical stability and high-efficiency emission at 1.8 μm may be used as potential laser materials for optical devices.