Weak antilocalization in a three-dimensional topological insulator based on a high-mobility HgTe film

The up-conversion luminescence of Er³⁺ from the ²H_11/2, ⁴S_3/2, and ⁴F_9/2 levels in nanocrystals of Y_0.95(1?x)Yb_0.95xEr_0.05PO₄ (x = 0, 0.3, 0.5, 0.7, 1) orthophosphates activated with Er³⁺ ions has been studied under the excitation of Yb³⁺ ions to the ²F_5/2 level by 972-nm cw laser radiation. Broadband radiation in the wavelength range of 370–900 nm has been observed at certain power densities of exciting laser radiation; this broadband radiation is absent in the case of excitation of the powders under study by pulsed laser radiation with a wavelength of 972 nm at a pulse repetition frequency of 10 Hz and a duration of a pulse of 15 ns. Experimental data indicating that this radiation is thermal in nature have been presented.     

Infrared to visible upconversion of Er3+ ions in Yb3+ doped fluorohafnate glasses

The upconversion of infrared radiation into green and red luminescence has been studied for Er³⁺ and Yb³⁺ ions in fluorohafnate glasses. At room temperature normalized upconversion efficiency of 8.4x10^-4 cm²/W has been obtained for the green emission (545 nm) of Er³⁺ in doped samples containing 4.5 mol% (Yb³⁺) and 0.75 mol% (Er³⁺) pumped by 974 nm light with an absorbed intensity of 2.5 mW/cm². Both green and red upconversion radiations slightly decrease with increasing temperature. Room-temperature measured efficiency is compared with the calculated one obtained from the rate equation model of Wright.     

Luminescence and excitation spectra of YAG:Nd excited by synchrotron radiation

The low-temperature 4f²5d→4f³ fast emission of Nd³⁺ from YAG:Nd³⁺ has been studied under excitation by synchrotron radiation. Additionally, 4f³→4f³ luminescence of Nd³⁺ has been observed and assigned to transitions from the ²F(2)_5/2 and ⁴F_3/2 multiplet terms. The observed experimental spectra of Nd³⁺ d-f emission and f-d excitation are well simulated by crystal-field calculations.     

Upconverted VUV luminescence of Nd and Er doped into LiYF4 crystals under XeF-laser excitation

The upconverted VUV (185 nm) and UV (230 and 260 nm) luminescence due to 5d-4f radiative transitions in Nd³⁺ ions doped into a LiYF₄ crystal has been obtained under excitation by 351/353 nm radiation from a XeF excimer laser. The maximum upconversion efficiency, defined as the ratio of intensity for 5d-4f luminescence to overall intensity for 5d-4f and 4f-4f luminescence from the ⁴D_3/2 Nd³⁺ level, has been estimated to be about 70% under optimal focusing conditions for XeF laser radiation. A redistribution of intensity between three main components of 5d-4f Nd³⁺ luminescence is observed under changing the excitation power density, which favors the most long-wavelength band (260 nm) at higher excitation density level. The effect is interpreted as being due to excited state absorption of radiation emitted. The upconverted VUV and UV luminescence from the high-lying ²F(2)_7/2 4f level of Er³⁺ doped into a LiYF₄ crystal has also been obtained under XeF-laser excitation the most intense line being at 280 nm from the spin-allowed transition to the ²H(2)_11/2 4f level of Er³⁺, but the efficiency of upconversion for Er³⁺ emission is low, less than 5%.     

Growth and spectral-luminescent study of SrMoO<Subscript>4</Subscript> crystals doped with Tm<Superscript>3+</Superscript> ions

SrMoO₄ crystals doped with Tm³⁺ ions have been produced from a melt using the Czochralski method; their spectral-luminescent characteristics have been studied, and laser radiation has been generated at the wavelength of 1.94 μm using laser-diode excitation. The high absorption section at the wavelength of 795 nm, the fairly high luminescence section, the long lifetime at the upper laser level ³F4 of 1.5 ms, and a wide luminescence band allow one to hope for developing efficient tunable Tm³⁺: SrMoO₄ crystal lasers with diode pumping in the range of 1.7–2.0 μm, which are capable of implementing SRS self-transformation of radiation into the middle IR band.     

Structural,thermal, and optical properties of Er3+/Yb3+ co-doped oxyhalide tellurite glasses,glass-ceramics and ceramics

Glass-ceramics and ceramics containing nano-crystals of different phases doped with Er³⁺/Yb³⁺ ions have been successfully prepared by heat treatment of the precursor oxyhalide glasses synthesized by the melt-quench method. X-ray diffraction patterns and transmission electron microscopy (TEM) images verify the precipitation of nano-crystals. Emission of Er³⁺ enhances several times when Yb³⁺ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase to a great extent when we approach to ceramics from glasses via glass-ceramics. The intensity of the blue and green emission bands increases much faster than the red and NIR emission bands. Intense upconversion emission observed by the naked eye has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible radiation takes place mainly via photon avalanche (PA) process.     

荧光捕获效应对Yb3+磷酸盐玻璃光谱性质的影响

测试了不同掺杂浓度和不同厚度下Yb³⁺磷酸盐玻璃的吸收光谱、荧光光谱和荧 光寿命，计算了积分吸收截面、吸收截面、受激发射截面、自发辐射寿命以及荧光有效线宽等光谱参数，讨论了荧光俘获效应对Yb³⁺磷酸盐玻璃光谱性质的影响.结果表明荧光俘 获效应随样品厚度和掺杂浓度的增加而增大.由于荧光俘获效应的存在使得测量的Yb^{3+磷酸盐玻璃荧光寿命明显长于计算的荧光寿命，在0.2mol%Yb₂O₃低掺 杂浓度下 关键词： 荧光俘获 掺镱磷酸盐玻璃 荧光光谱}     

Dosimetric properties of rare earth doped LiCaBO3 thermoluminescence phosphors

Lithium Calcium borate (LiCaBO₃) polycrystalline thermoluminescence (TL) phosphor doped with rare earth (RE³⁺) elements has been synthesized by high temperature solid state diffusion reaction. The reaction has produced a very stable crystalline LiCaBO₃:RE³⁺ phosphors. Among these RE³⁺ doped phosphors thulium doped material showed maximum TL sensitivity with favorable glow curve shape. TL glow curve of gamma irradiated LiCaBO₃:Tm³⁺ samples had shown two major well-separated glow peaks at 230 and 430 °C. The glow peak at 430 °C is almost thrice the intensity of the glow peak at 230 °C. The TL sensitivity of the phosphor to gamma radiation was about eight times that of TLD-100 (LiF). Photoluminescence and TL emission spectra showed the characteristic Tm³⁺ peaks. TL response to gamma radiation dose was linear up to 10³ Gy. Post-irradiation TL fading on storage in room temperature and elevated temperatures was studied in LiCaBO₃:Tm³⁺ phosphor.     

5d–4f luminescence of Ce3+, Gd3+ and Lu3+ in LiCaAlF6

The emission and excitation spectra as well as decay kinetics of luminescence due to 5d–4f transitions in Ce³⁺, Gd³⁺ and Lu³⁺ ions doped into LiCaAlF₆ crystals have been analyzed with high spectral and time resolution using synchrotron radiation for excitation. The rich fine structure originating from electronic origins of transitions and their phonon replica has been well resolved and identified. Experimental data are compared with the spectra simulated in the framework of the semiphenomenological models of the crystal field and the crystal lattice dynamics.     

On the influence of dopant ions on blue emission in kgw crystal excited by infrared laser radiation

The role of doping by Nd³⁺ and Tm³⁺ ions in the generation of blue emission in a KGW crystal excited by infrared radiation has been analyzed. Experimental measurements of the emission characteristics and theoretical results of modeling emission spectra of the doping ions are compared. A qualitative difference is shown between the calculated Tm³⁺ luminescence spectrum and that observed in the experiment. Data on branching ratios of luminescence from the ²P_1/2 level of the Nd³⁺ ions suggest a low emission efficiency from this multiplet in the blue spectral region.     

Luminescence properties of phosphors based on Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> (TbAG) terbium-aluminum garnet

The processes of excitation energy transfer in phosphors based on single-crystal Tb₃Al₅O₁₂:Ce (TbAG:Ce) and Tb₃Al₅O₁₂:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb³⁺ cations) to Ce³⁺ and Eu³⁺ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb³⁺ ions to Ce³⁺ and Eu³⁺ ions and from Ce³⁺ ions to Eu³⁺ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb³⁺ cation sublattice.     

Growth, spectroscopic characteristics and laser potential of Yb3+:Ca3La2(BO3)4 crystal

Crystal of Yb³⁺-doped Ca₃La₂(BO₃)₄ has been grown by the Czochralski technique. The room temperature absorption and fluorescence spectra of the crystal have been investigated. The result showed that this crystal exhibits broad absorption and emission with the FWHM of 11 nm at 978 nm and 66 nm FWHM at 1025 nm, respectively. The stimulated emission cross-section of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg method, respectively. The room temperature fluorescence decay curves of ² F _5/2 manifold of Yb³⁺ ions were recorded for both crystal and powder samples. The effect of radiation tapping on the spectroscopic properties is discussed. The result that the lifetime of the powder sample is shorter than that of the bulk sample demonstrates the existence of radiation trapping effect. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.     

UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO₄:Eu³⁺, Eu²⁺) and terbium doped calcium fluoride (CaF₂:Tb³⁺) phosphors have been studied. PL measurements suggest conversion of Eu³⁺ to Eu²⁺ on 254 nm irradiation corresponding to charge transfer band of Eu³⁺ ions and reduction of Eu²⁺ ions with 365 nm illumination representing a f–d transition of Eu²⁺ ions. Similar studies carried out on CaF₂:Tb³⁺ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO₄:Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF₂:Tb³⁺ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities.     

Upconversion luminescence of Er/Yb-codoped natrium-germanium-bismuth glasses

The absorption and upconversion fluorescence spectra of a series of Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth glasses have been studied. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er³⁺ based on the Judd-Ofelt theory. At room temperature, an upconversion efficiency of 6.1×10⁻² has been obtained for the green emission from the glass with 0.5 wt% Er₂O₃ and 3.0 wt% Yb₂O₃ pumped by 980 nm radiation with an intensity of 270 W/cm². And the “standardized” efficiency for green upconversion light is higher than that reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices.     

Enhancement of upconversion intensity in Er3+ doped tellurite glass in presence of Yb3+

TeO₂–PbO glasses doped/codoped with Er³⁺/Er³⁺-Yb³⁺ ions have been fabricated by melting and quenching method. Efficient frequency upconversion emissions spanning from blue to red regions corresponding to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions, respectively, upon excitation with 976 nm diode laser radiation have been observed. The variations observed in the intensity of whole upconversion emission spectra due to the presence of the Yb³⁺ ions are reported and discussed in detail.     

Enhancement of up-conversion luminescence in Zn2SiO4:Yb3+, Er3+ by co-doping with Li+ or Bi3+

Yb³⁺/Er³⁺ co-doped Zn₂SiO₄ ceramics are rapidly synthesized by the microwave radiation method. Green and red up-conversion emissions are observed in Zn₂SiO₄: Yb³⁺, Er³⁺ ceramics under 980 nm excitation. The influence of co-doped Li⁺ or Bi³⁺ ion on luminescence intensity for the phosphors has been investigated. At Li⁺ or Bi³⁺ doping concentration of 1 mol%, up-converted green emission can be increased by 6 times and 20 times, respectively. It is believed that co-doped Li⁺ or Bi³⁺ ion results in the local distortion of Er³⁺ in Zn₂SiO₄, increasing the intra-4f transitions of Er³⁺ ions. The local distortion is proved by spectral probing method with Eu³⁺.     

Photodisintegration of 11Li and Radiation Capture of Two Neutrons by 9Li

Photodisintegration of ¹¹Li and radiation capture of two neutrons by ⁹Li are studied in the frame of algebraic version of resonating group method and in asymptotic potential approximation. The behavior of the scattering phases shows on the existence of J ^π=3/2⁺ and J ^π=5/2⁺ resonances in continuum above the three-body decay threshold ¹¹Li→⁹Li+n + n. The cross-section of photodisintegration as well as the cross-section of radiation capture have been received. Energetic dependence of the first one is in good correspondence with the experimental data.     

Integral Method o Reciprocity in the Spectroscopy of Laser Crystals with Impurity Centers

A new method of determining the stimulated emission cross-section spectra from the absorption cross-section spectra, which we call the integral method of reciprocity, is suggested it does not require knowledge of the structure of the impurity-center electron levels. Based on this method, formulas for calculating the radiation lifetime of impurity centers in crystals have been derived. The effectiveness of the integral method of reciprocity was demonstrated in determining the stimulated emission cross sections and radiation lifetime of an ytterbium ion in the laser crystals Yb³⁺:KYW and Yb³⁺:KGW.     

Optical properties of UV-induced color centers in a KY3F10:Ce3+ crystal

The evolution of color centers induced in a KY₃F₁₀:Ce³⁺ crystal by UV radiation has been observed and interpreted. It has been revealed that, initially, the UV irradiation of the KY₃F₁₀:Ce³⁺ crystal induces the formation of color centers predominantly of the F-type, which, in a short time period of about ten minutes, are transformed into complex color centers of the F ₂-type, as well as into impurity color centers. Based on the data obtained, a diagram of energy states of the crystal, dopant, and color centers has been constructed, on which most probable processes that are caused by electronic transitions occurring in the KYF:Ce³⁺ crystal after its UV irradiation have been indicated.     

Mn, Cr-co-doped MgAl2O4 phosphors for white LEDs

The Mn-, Cr-doped and Mn, Cr-co-doped MgAl₂O₄ powders have been synthesized via a gel-solid reaction method. Energy transfer from Mn²⁺ to Cr³⁺ has been observed for the first time in the co-doped MgAl₂O₄ phosphors. When excited with blue light with a wavelength of 450 nm at room temperature, both green emission from Mn²⁺ around 520 nm and red emission from Cr³⁺ around 675and 693 nm were generated. Moreover, the color of the emission can be modified by controlling the doping concentrations of Mn²⁺ and Cr³⁺. Therefore, MgAl₂O₄: Mn²⁺, Cr³⁺ could be used as a single-phased phosphor for white LED with a blue LED chip. The energy transfer in terms of Mn²⁺ to Cr³⁺ is determined by means of radiation and reabsorption.