Intra and inter-ionic multiphonon transitions in rare earth doped crystals

A theory has been developed for non-radiative multiphonon transitions in ionic crystals doped by RE-impurities. The degeneration of final electronic states has been taken into account in the framework of the first cumulant approximation. An analytical expression has been obtained for the rate of non-resonant energy transfer caused by electrostatic inter-ionic interaction and numerical estimations for Yb → Tm and Yb → Ho transitions in YAlO₃ and YLiF₄ crystals are listed. The intra-center multiphonon non-radiative relaxation has been considered in the case where acoustical modes of lattice vibrations are the promoting ones.     

Site selective spectroscopy of rare earth doped ThO2

The individual sites present in ThO₂ doped with Eu³⁺ and Er³⁺ have been studied by site selective spectroscopy. A cubic site corresponding to a rare earth charge compensated distantly and two sites having local charge compensation have been identified. One of the locally compensated sites is present only at moderate temperature while the other is formed at higher temperatures and is stable to high temperatures. The measurements are related to catalytically excited fluorescence of ThO₂, previous luminescence measurements, and magnetic resonance experiments that observe the presence of local F^_ charge compensation of rare earth dopants.     

Radio-frequency spectrum analyzers based on rare earth ion doped crystals

We review recent demonstrations of wide band radio frequency (rf) spectral analyzers based on spectral hole burning technology. The optically carried rf signal can be analyzed with sub-MHz resolution over tens of GHz instantaneous bandwidth. PACS 42.50.Md; 76.30.Kg; 42.79.Hp; 95.55.Fm; 95.55.Jz     

14th International Feofilov Symposium on spectroscopy of crystals doped with rare earth and transition metal ions

Condensed-Matter Spectroscopy

14th International Feofilov Symposium on spectroscopy of crystals doped with rare earth and transition metal ions     

Infrared-to-visible and infrared-to-violet upconversion fluorescence of rare earth doped LaF3 nanocrystals

This paper reports that hexagonal-phase LaF3：Yb0.20^3＋,Er0.02^3＋ and LaF3：Yb0.20^3＋, Tm0.02^3＋ nanocrystals （NCs） were synthesized via a hydrothermal method. The transmission electron microscopy, selected area electron diffraction, powder x-ray diffraction, and thermogravimetric analysis are used to characterize the NCs. Under 980 nm excitation, the Yb^3＋/Er^3＋ and Yb^3＋/Tm^3＋ codoped NCs colloidal solutions present bright green and blue upconversion fluorescence, respectively. These NCs show efficient infrared-to-violet and infrared-to-visible upconversion. The upconversion fluo- rescence mechanisms of LaF2：Yb0.20^3＋, Er0.02^3＋ and LaF3：Yb0.20^3＋,Tm0.02^3＋ NCs are investigated with a 980-nm diode laser as excitation source.     

Surface effect of nanocrystals doped with rare earth ions enriched on surface and its application in upconversion luminescence

By employing a certain proportion of hydrogen peroxide, ammonia, ammonium fluoride, and ethylene diamine tetraacetic acid (EDTA) as precipitator, well-crystallized LaOF:Eu3+ and LaOF:Yb3+, Er3+ nanocrystals are synthe- sized by using the chemical co-precipitation method. The structural properties of these samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) spectra. The results show that all the samples have an average size below 70 nm, which decreases gradually with the increase of the EDTA content, and a certain number of EDTA molecules are coupled with doped ions on the surfaces of nanocrystals. Most of the doped ions are proved to be enriched on the surfaces of nanocrystals and surrounded by the high energy vibration groups and bonds in EDTA molecules. The observed differences in upconversion emission spectrum among the different LaOF:Yb3+, Er3+ nanocrystals are explained by the different two-photon upconversion mechanisms. Especially, in the LaOF:Yb3+, Er3+ nanocrystals with EDTA, the two-photon processes that contain several special cross-relaxation processes are introduced to analyse the corresponding upconversion mechanisms.     

Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y₂SiO₅ (YSO), Lu₂SiO₅ (LSO), (Lu_0.5Y_0.5)₂SiO₅ (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm⁻¹ region assigned to the modes of SiO₄ and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm⁻¹ are an indication of impurities. The (SiO₄)⁴⁻ tetrahedra are characterized by bands near 200 cm⁻¹ which show a separation of the components of ν₄ and ν₂, in the 500–700 cm⁻¹ region which are attributed to the distorting bending vibration and in the 880–1000 cm⁻¹ region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm⁻¹ region of Re₂SiO₅ were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.     

Photodichroic crystals for coherent optical data processing

The use of photodichroic alkali halide crystals as re-usable input, storage, and filter plane elements in a coherent optical computer are reviewed. Various recording methods and applications are presented with emphasis on the use of the M and M_A centres in NaF at room temperature.     

Phase changes in cubic rare earth crystals

An explanation is offered of the structural transitions and magnetic orderings in the cubic rare earth compounds LnX with particular emphasis on the anomalous spin arrangements observed in HoP, DyP and DyAs and in ErSb and ErP.     

Relation between optical breakdown field and stokes spectral broadening

The process which limits the diameter of self focal spots must also limit the Stokes self phase modulated spectral width. A simple analysis is consistent with data for nsec pulses in organic liquids.     

第一性原理研究稀土掺杂ZnO结构的光电性质

基于密度泛函理论的第一性原理平面波超软赝势方法,运用Castep计算分析了Er, Gd两种稀土元素掺杂的ZnO结构, 对本征ZnO和掺杂晶体的能带结构、态密度以及光学性质进行了分析对比. 由掺杂前后的结果分析发现,稀土掺杂的ZnO结构引入了由稀土原子贡献的导电载流子, 增强了体系的电导率, 费米能级上移进入导带. 研究表明由于稀土元素的掺入, ZnO结构在费米能级附近出现了杂质能带, 这是由稀土的4f态电子所形成. 同时, 纯净ZnO与Er-ZnO, Gd-ZnO和(Er, Gd)-ZnO的介电函数虚部有明显的差异. 在光学性质上, 掺杂ZnO在可见光区的吸收系数和反射率都比纯净ZnO高, 能量损失峰出现红移现象. 关键词： ZnO 稀土 掺杂 第一性原理     

Conduction electron polarization in ferromagnetic rare earth crystals

We show that the average spin per atom in ferromagnetic rare earth metals is enhanced by means of a net spin polarisation of conduction electrons, arising as a consequence of multiple scattering of the conduction electrons.     

High resolution atomic coherent control via spectral phase manipulation of an optical frequency comb

We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.     

稀土元素(Y,La)掺杂ZnO的电子结构和光学性质

采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算了未掺杂ZnO和稀土(Y,La)掺杂ZnO体系的空间结构、能带、电子态密度与光学性质.结果表明,掺杂后体系的形成能减小,稳定性变强,带隙展宽,费米能级进入导带中,体系呈金属性,载流子发生简并,形成简并半导体.定性分析了掺杂后光学性质的变化. 关键词： 氧化锌 掺杂 第一性原理     

Diffuse phase transition in rare earth ion doped SBN

The diffuse transition of a rare earth ion doped SBN (Ba_xSr_1?xNb₂O₆) was studied by measuring the spontaneous polarization P_s, and the dielectric constant ?. The phase transition of SBN can be regarded as a special case of a second order transition.     

稀土元素掺杂的Hf基栅介质材料研究进展

随着金属氧化物半导体场效应管(MOSFETs)等比缩小到45 nm技术节点,具有高介电常数的栅介质材料(高k材料)取代传统的SiO₂已经成为必然,然而Hf基高k材料在实际应用中仍然存在许多不足,而稀土元素掺杂在提高Hf基栅介质材料的k值、降低缺陷密度、调整MOSFETs器件的阈值电压等方面表现出明显的优势.本文综述了Hf基高k材料的发展历程,面临的挑战,稀土掺杂对Hf基高k材料性能的调节以及未来研究的趋势. 关键词： k栅介质')" href="#">Hf基高k栅介质 稀土掺杂 氧空位缺陷 有效功函数     

Electrical relaxation in rare earth doped cubic lead fluoride

Audio frequency complex impedance measurements are performed over the temperature range 5.5-380 K on lead fluoride doped with ten rare earths and lanthanum at various concentrations. It is found that the complexity of the relaxation spectrum increases as the size of the trivalent ion decreases. Specifically, for the largest rare earths, only one relaxation is found. That relaxation is different from the cases in the alkaline earth fluorides where only one relaxation is observed in that the reorientation enthalpy depends strongly upon ion size. Double-doped samples are studied to determine whether the relaxation is due to a simple site or a cluster. For the smallest rare earths, however, at least nine relaxations are found. The concentration studies indicate multiple relaxations for certain sites. Both simple sites and clusters are observed for small rare earths.     

Zero point shift in rare earth doped CaF2

The line position of the 4f ⁷(⁸ S _7/2)→4f ⁶5d (4130 Å) transition in Eu:CaF₂ has been measured as well as its shift under the action of uniaxial stress. These data are used to estimate the isotope shift due to the zero point vibrations. There is reasonable agreement with that measured directly in Sm:CaF₂.