Quantum cutting downconversion by cooperative energy transfer from Bi3+ to Yb3+ in Y2O3 phosphor

Bi~(3+) and Yb~(3+) codoped cubic Y2O3 phosphors are prepared by pechini sol-gel method.Strong near-infrared (NIR) emission around 980 nm from Yb~(3+)(2F5/2 → 2F7/2) is observed under ultraviolet light excitation.A broad excitation band ranging from 320 to 360 nm,owing to the 6s 2 →6s6p transition of Bi~(3+) ions,is recorded when the Yb~(3+) emission is monitored,which suggests a very efficient energy transfer from Bi~(3+) ions to Yb~(3+) ions.The Yb~(3+) concentration dependences of both the Bi~(3+) and the Yb~(3+) emissions are investigated.The decay curve of Bi ~(3+) emission under the excitation of 355 nm pulse laser is used to explore the Bi~(3+) →Yb~(3+) energy transfer process.Cooperative energy transfer (CET) is discussed as a possible mechanism for the near-infrared emission.     

Visible Upconversion Emission in Er3＋—Doped GeO2—PbO—PbF2 Glass

The upconversion fluorescence emission of Er3 -doped 60GeO2-2OPbO-2OPbF2 glass was experimentally investigated under the pump of 976-nm laser diode. The results reveal the existence of intense emission bands centred around 524, 545, and 657nm at room temperature. The green emission at 524 and 545nm is due to the 4S3/2 2 Hll/2→ 4I15/2 transition and the red emission of 657nm originates from the 4F9/2-→4I15/2 transition of Er3 . The quadratic dependence of the green and red emissions on excitation power indicates that a two-photonabsorption process occurs under the 976-nm excitation. The excited- state absorption from 4I ll/2 and the cross relaxation between two Er3 ions in the 4I ll/2 state contribute to the green emission. The red emission at 657nm is attributed to the excited-state absorption and cross relaxation processes in the 4I13/2 level as well as the 4S3/2 level nonradiative transition of Er3 .     

Growth and optical properties of Cr~（3＋）-doped CdWO_4 single crystals

A high-quality Cr 3+:CdWO4 single crystal at a size of approximatelyΦ25×80 mm is grown using the Bridgman method with CdO,WO3,and Cr2O3 as raw materials and their molar ratio of 100:100:0.5.The temperature gradient of solid-liquid interface at growth is approximately 50?C/cm and the growth rate is 0.05 mm/h.The X-ray diffraction(XRD),absorption,excitation,and emission spectra of different parts of the as-grown and O2-annealed crystals are investigated.Two strong broad optical absorption bands of about 472 and 708 nm are observed,and they are associated with the transitions 4 A2→ 4 T1 and 4 A2→ 4 T2.The weak 4 T2→ 2 E transition(the R-line)at 632 nm is also observed.The crystal-field parameter Dq and the Racah parameters B and C are estimated to be 1 412.4,776.8,and 3 427.6 cm? 1,respectively,according to the absorption spectra and crystal-splitting theory.A broadband fluorescence at about 1 000 nm due to 4 T2→ 4 A2 transition is produced by exciting the samples at 675 nm.After being annealed in an O2 atmosphere,the crystals become more transparent,while the effective light absorption of Cr 3+ ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO4 crystal after annealing.     

Identification of Three Weak Lines and Their Influences on Diagnostics of Electron Temperature and Density in Astrophysical Plasmas

By comparing of the spectra from the Chandra LETGs observation with the synthetic spectra of argon, we identify two weak emission lines, that is, the Ar XV 27.470A line with transition 2s3p ^1p1 - 2s^2 ^1So and the Ar XVI 27.872A line with transition 3d ^2D3/2 - 2p ^2P1/2, which blend with the N Ⅶ Lyα emission line. Several secondorder spectral lines are also identified, one of which is the second-order Fe XⅧ 14.534A line with transition 2p^4(^3p)3d ^2F5/2 - 2p^5 ^2P3/2, which blends with the inter-combination line of He-like N VI. In order to study the effects of these new identified weak lines on the electron temperature and density, we diagnose the two parameters using the intensity ratio of triplets of the He-like N Ⅵ and that of resonance lines of H- and He-like N. In the literature, there is a discrepancy of the temperatures deduced from N Ⅵ from other He-like ions, such as C V and O Ⅶ. The discrepancy disappears after the contribution of these weak lines is taken into account.     

First Principles Study on Electronic Structures of Mn^2＋：CdMoO4 Crystals

Electronic structures of the Mn^2＋ ：CdMoO4 crystal axe studied within the framework of the fully relativistic self-consistent Dirac Slater theory, using a numerically discrete variation （DV-Xα） method. The calculated results indicate that the 3d states of Mn have donor energy level in the forbidden band of CdMoO4 crystal. The O^2- transition energy of O 2p→Mn 3d is 3.12eV under excitation corresponding electronic transition being O^2-＋Mn^2＋→↑hvex=3.12 eV O^-- ＋Mn^＋→↑hvem O^2-＋Mn^2＋. It is predicted that the wavelength of emission should be located in the range of the 500-600nm. Thus the 500-600mm emission bands peaking at 550nm （2.25eV） of CdMoO4 crystal under excitation may be related to the Mn-like dopant ion in CdMoO4 crystal.     

Efficient 2.7-μm emission in Er3＋-doped bismuth germanate glass pumped by 980-nm laser diode

An Er 3+-doped lead-free bismuth germanate glass is synthesized. Its 2.7-μm emission property is analyzed, and the efficient 2.7-μm emission from the glass is observed under 980-nm laser diode excitation. The prepared glass possesses high spontaneous transition probability (64.8 s 1 ) and a large calculated emission cross section (6.61×10 21 cm 2 ) corresponding to the 4I11/2→4I13/2 transition. The multiphonon relaxation rate for the excited state 4I11/2 is only 236 s 1 . Therefore, the excellent spectroscopic properties and outstanding thermal stability suggest that this glass is a suitable host for developing solid-state lasers operating in the mid-infrared.     

Observation of four-wave mixing in caesium atoms using a noncycling transition

In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition $6{\rm S}_{1/2}F=4\to6{\rm P}_{3/2}F'=4$, and meanwhile the probe frequency is scanned across the $6{\rm S}_{1/2}F=4 \to6{\rm P}_{3/2}$ transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with $6{\rm S}_{1/2} F=3\to 6{\rm P}_{3/2}F'=4$ transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.     

A novel yellow emitting phosphor Dy3+, Bi3+ co-doped YVO4 potentially for white light emitting diodes

Novel Y1 x yVO4:xDy3+,yBi3+(0.01 ≤ x ≤ 0.05,0 ≤ y ≤ 0.20) phosphors for light emitting diode(LED) were successfully synthesised by solid-state reaction.The calculation results of electronic structure show that YVO4 has a direct band gap with 3 eV at G.The top of the valence band is dominated by O 2p state and the bottom of the conduction band is mainly composed of O 2p and V 3d states.An efficient yellow emission under near-ultraviolet(365 nm) excitation is observed.Compared with the pure YVO4:Dy3+ samples,the Dy3+,Bi3+ co-doped samples show a more intensive emission peak(at 574 nm) and a new broad emission band(450-770 nm),due to the 4F9/2 6H13/2 transition of Dy3+ and the emission of the VO3 4 Bi3+ complex respectively.The optimum chromaticity index of Y1 x yVO4:xDy3+,yBi3+(0.01 ≤ x ≤ 0.05,0 ≤ y ≤ 0.20) is(0.447,0.497),which indicates that YVO4:Dy3+,Bi3+ has higher colour saturation than the commercial phosphor YAG:Ce3+.The effects of concentration of Dy3+,Bi3+,electric states and the photoluminescence properties are discussed in details.     

Temperature dependence of the photoluminescence of MnS/ZnS core–shell quantum dots

The temperature dependence of the photoluminescence（PL） from Mn S/Zn S core–shell quantum dots is investigated in a temperature range of 8 K–300 K. The orange emission from the ^4T1→^6A1transition of Mn^2＋ions and the blue emission related to the trapped surface state are observed in the Mn S/Zn S core–shell quantum dots. As the temperature increases, the orange emission is shifted toward a shorter wavelength while the blue emission is shifted towards the longer wavelength. Both the orange and blue emissions reduce their intensities with the increase of temperature but the blue emission is quenched faster. The temperature-dependent luminescence intensities of the two emissions are well explained by the thermal quenching theory.     

Investigation of AlGaN/GaN fluorine plasma treatment enhancement-mode high electronic mobility transistors by frequency-dependent capacitance and conductance analysis

This paper reports fluorine plasma treatment enhancement-mode HEMTs (high electronic mobility transistors) EHEMTs and conventional depletion-mode HEMTs DHEMTs fabricated on one wafer using separate litho-photography technology. It finds that fluorine plasma etches the AlGaN at a slow rate by capacitance--voltage measurement. Using capacitance--frequency measurement, it finds one type of trap in conventional DHEMTs with τ_T=(0.5-6) ms and D_T= (1 - 5) × 10¹³ cm^-2·eV^-1. Two types of trap are found in fluorine plasma treatment EHEMTs, fast with τ_T(f)=(0.2-2) μs and slow with τ_T(s)=(0.5-6) ms. The density of trap states evaluated on the EHEMTs is D_T(f)=(1 - 3) × 10¹² cm^-2·eV^-1 and D_T(s)=(2 - 6) × 10¹² cm^-2·eV^-1 for the fast and slow traps, respectively. The result shows that the fluorine plasma treatment reduces the slow trap density by about one order, but introduces a new type of fast trap. The slow trap is suggested to be a surface trap, related to the gate leakage current.     

Ca4LaNbMo4O20:Pr3+荧光粉的发光性质

采用高温固相法成功制备出荧光粉Ca₄LaNbMo₄O₂₀:Pr³⁺,通过X射线衍射分析了样品的结构,其结构与CaMoO₄结构相似。在Ca₄LaNbMo₄O₂₀:Pr³⁺的激发光谱中出现了NbO₄^3-和MoO₄^2-的电荷迁移(CTS)吸收和Pr³⁺离子的4f→4f5d激发跃迁,以及Pr³⁺-金属离子的价间电荷迁移(IVCT)吸收;另外在420~520 nm处,还观测到属于Pr³⁺离子的典型f-f激发跃迁。发射光谱中,在452 nm激发下,主要出现绿光和红光两种发射,其峰值位于490 nm和607 nm处,分别是Pr³⁺的³P₀→³H₄和¹D₂→³H₄的跃迁作用;在紫外287 nm激发下出现NbO₄^3-和MoO₄^2-发射和Pr³⁺离子的4f5d→4f跃迁宽带,以及Pr³⁺离子的4f→4f发射峰。     

Evidence for Pauli exchange leading to excited-state enhancement in electron transfer

Single- and double-electron transfer to autoionizing 1s2l2l(') configurations in fluorine ions have been investigated for 1.1 MeV/u collisions of F7+ and F8+ with He and Ne. The resulting Auger electron emission spectra show anomolously large intensities for the formation of the metastable 1s(2s2p 3P) 4P state compared to the similarly configured 1s(2s2p 3P) 2P- and 1s(2s2p 1P) 2P+ states. The large 4P intensity, which cannot be explained on the basis of spin statistics, is attributed instead to the Pauli exchange of similarly aligned electrons.     

掺杂三价铽离子的碱土金属钨酸盐的光谱特性研究

本文合成了一系列掺杂三价铽离子的碱土金属钨酸盐,测定了晶体的X射线粉末衍射数据及发射光谱和激发光谱.所合成的化合物均属四方晶系,I41/a空间群,晶胞多数随金属离子半径的增大而增大.研究了在这些晶体中三价铽离子5D3→7Fi和5D4→7Fi跃迁发射的激发态及其能量传递机理和浓度猝灭机制.讨论了发射光谱和激发光谱与铽离子浓度、金属离子半径及铽离子在晶体中的溶解度的关系.     

Oxygen chemisorption and initial oxidation of Cr(110)

The initial stages of the interaction of oxygen with a Cr(110) surface have been investigated at 300 K by LEED, AES, electron energy loss spectroscopy (ELS), secondary electron emission spectroscopy (SES) and work-function change measurement (Δφ). In the exposure region up to 2 L, the clean-surface ELS peaks due to interband transition weakened and then disappeared, while the ～5.8 and 10 eV loss peaks attributed to the O 2p → Cr 3d transitions appeared, accompanied with a work-function increase (Δφ = +0.19 eV at2L). In the region 2–6 L the work function decreased to below the original clean-surface value (Δφ_min = ?0.24 eV at6L), and five additional ELS peaks were observed at ～2, 4, 11, 20 and 32 eV: the 2 and 4 eV peaks are ascribed to the ligand-field d → d transitions of a Cr³⁺ ion, the 11 eV peak to the O 2p → Cr 4s transition, the 20 eV peak to the Cr 3d → 4p transition of a Cr³⁺ ion and the 32 eV peak probably to the Cr 3d → 4f transition. A new SES peak at 6.1 eV, being attributed to the final state for t he 11 eV ELS peak, was observed at above 3 L and identified as due to the unfilled Cr 4s state caused by charge transfer from Cr to oxygen sites in this region. In the region 6–15 L the work function increased again (Δφ_max = +0.32 eV at15 L), the 33 and 46 eV Auger peaks due to respectively the M_2,3(Cr)L_2,3(O)L_2,3(O) cross transition and the M_2,3VV transition of the oxide appeared and the 26 eV ELS peak due to the O 2s → Cr 4s transition was also observed. Above 10 L, the ELS spectra were found to be practically the same as that of Cr₂O₃. Finally, above 15 L, the work function decreased slowly (Δφ = +0.13 eV at40L). From these results, the oxygen interaction with a Cr(110) surface can be classified into four different stages: (1) dissociative chemisorption stage up to 2 L, (2) incorporation of O adatoms into the Cr selvedge between 2–6 L, (3) rapid oxidation between 6–15 L leading to the formation of thin Cr₂O₃ film, and (4) slow thickening of Cr₂O₃ above 15 L. The change in the Cr 3p excitation spectrum during oxidation was also investigated. The oxide growth can be interpreted on the basis of a modified coupled current approach of low-temperature oxidation of metals.     

The electronic structures of the core and valence ion states of metal oxides

SCF-Xα SW MO calculations on metal core ion hole states and X-ray emission (XES) and X-ray photoelectron (XPS) transition states of the non- transition metal oxidic clusters MgO₆^10?, AlO₄^5? and SiO₄^4? show relative valence orbital energies to be virtually unaffected by the creation of valence orbital or metal core orbital holes. Accordingly, valence orbital energies derived from XPS and XES are directly comparable and may be correlated to generate empirical MO diagrams. In addition, charge relaxation about the metal core hole is small and valence orbital compositions are little changed in the core hole state. On the other hand, for the transition metal oxidic clusters FeO₆^10?, CrO₆^9? and TiO₆^8? relative valence orbital energies are sharply changed by a metal core orbital or crystal field orbital hole, the energy lowering of an orbital increasing with its degree of metal character. Consequently O 2p nonbonding → M 3d-O 2p antibonding (crystal field) energies are reduced, while M 3d bonding → O 2p nonbonding and M 3d-O 2p antibonding → M 4s,p-O 2p antibonding (conduction band) energies increase. Charge relaxation about the core hole is virtually complete in the transition metal oxides and substantial changes are observed in the composition of those valence orbitals with appreciable M 3d character. This change in composition is greater for e _g than for t_2g orbitals and increases as the separation of the e_g crystal field (CF) orbitals and the O 2p nonbonding orbital set decreases. Based on the hole state MO diagrams the higher energy XPS satellite in TiO₂ (at about 13 eV) is assigned to a valence → conduction band transition. The UV PES satellites at 8.2 eV in Cr₂O₃ and 9.3 eV in FeO are tentatively assigned to similar transitions to conduction band orbitals, although the closeness in energy of the crystal field and O 2p nonbonding orbitals in the valence orbital hole state prevents a definite assignment on energy criteria alone. However the calculations do clearly show that charge transfer transitions of the e_g bonding → e_g crystal field orbital type would generally occur at lower energy than is consistent with observed satellite structure.A core electron hole has little effect upon relative orbital energies and is only slightly neutralized by valence electron redistribution for MgO and SiO₂. For the transition metal oxides a core hole lowers the relative energies of M3d containing orbitals by large amounts, reducing O → M charge transfer and increasing M 3d crystal field → conduction band energies. Large and sometimes overcomplete neutralization of the core hole is observed, increasing from CrO₆^9? to FeO₆^10? to TiO₆^8?. as the O → M charge transfer energy declines.High energy XPS satellites in TiO₂ may be assigned to O 2p nonbonding → conduction band transitions while lower energy UV PES satellites in FeO and Cr₂O₃ arise from crystal field or O 2p nonbonding → conduction band excitations. Our “shake-up” assignment for FeO₆^10?, CrO₆^9? and TiO₆^8? are less than definitive because no procedure has yet been developed to calculate “shake-up” intensities resulting from transitions of the type described. However the results do allow a critical evaluation of earlier qualitative predictions of core and valence hole effects. First, we find that the comparison of hole or valence state ionic systems with equilibrium distance systems of higher nuclear and/or cation charge (e.g. the comparison of the FeO₆^10? Fe 2p core hole state to Co₃O₄) is dangerous. For example, larger MO distances in the ion states substantially reduce crystal field splittings. Second, core and CF orbital holes sharply reduce O → M charge transfer energies, giving 2e_g → 3e_g energy separations which are generally too small to match observed satellite energies. Third, highest occupied CF-conduction band energies are only about 4–5 eV in the ground states, but increase to about 7–11 eV in the core and valence hole states of the transition metal oxides studied. The energetic arguments presented thus support the idea of CF and/or O 2p nonbonding → conduction band excitations as assignments for “shake-up” satellites, at least in oxides of metals near the beginning of the transition series.     

Nd~(3+)/Yb~(3+)掺杂YNbO_4粉末上转换发光特性

采用高温固相法,以50Nb_2O_5-40Y2O_3-2Nd2O_3-8Yb_2O_3的量比在1 300℃下制备Nd~(3+)/Yb~(3+)掺杂YNbO_4粉末样品。运用Judd-Ofelt理论研究样品光谱特性。由吸收谱中各吸收峰面积计算得到谱线强度参数Ωλ(λ=2,4,6),进而得出理论振子强度及实验振子强度,二者均方根偏差δ_(rms)=1.618×10-7。计算了Nd~(3+)能级4F3/2→4IJ'(J'=15/2,13/2,11/2,9/2)跃迁几率、跃迁分支比和能级寿命。4F3/2→4I11/2跃迁分支比最高(56.91%),对应波长1 062 nm。且亚稳态4F3/2能级寿命较长,为1.435 2 ms,适合作为上转换中间能级。在980 nm半导体激光器激发下,观测到波长为487,541,662 nm上转换发光,分别对应于Nd~(3+)的2G9/2→4I9/2、4G7/2→4I9/2和4G7/2→4I13/2辐射跃迁。通过样品上转换发射功率与激光器工作电流进行的曲线拟合,得到吸收光子数目依次为2.06,1.99,2.15,确定3个发射峰均对应于双光子吸收。     

977nm抽运下掺铒碲酸盐基氧卤玻璃的光谱特性

研究了掺铒TeO2-ZnO-PbCl2碲酸盐基氧卤玻璃在977nm激光二极管抽运下的发光和上转换发光特性，结果发现除红外153μm4I13/2→４I15/2发光外（荧光半高宽高达69nm），该玻璃还存在很强的２Ｈ11/2→４I15/2（527nm），４Ｓ3/2→４I15/2（549nm）和４Ｆ９／２→４Ｉ１５／２（666nm）可见上转换发光.应用Judd-Ofelt理论计算得到玻璃强度参数Ωt（t=2，4，6）分别为Ω2=587×10-20cm2，Ω4=208×10-20cm2，Ω6=116×10-20cm2，计算了铒离子跃迁振子强度、自发辐射概率、荧光分支比、荧光寿命等光谱参量.应用McCumber理论计算得153μm处的玻璃受激发射截面可达875×10-21cm2实验结果表明，与硅酸盐玻璃、磷酸盐玻璃、氟化物玻璃等比较，掺铒碲酸盐基氧卤玻璃在宽带掺铒光纤放大器和上转换激光器中有着极大的研究和应用潜力. 关键词： 掺Er3+ 碲酸盐玻璃 氧卤玻璃 Judd-Ofelt理论 光谱性质     

大气压空气脉冲流光放电等离子体发射光谱分析

在大气压条件下采用尖-尖电极放电系统得到了稳定的放电等离子体, 并应用发射光谱方法对放电等离子体进行了实验研究。等离子体发射光谱呈现连续谱背景迭加分立谱的形式。连续谱背景来源于放电等离子体内轫致辐射和复合辐射过程; 分立谱归属为N2 C3∏u →B3∏g , N+, N, O的荧光辐射。N+荧光辐射对应的上能级电子组态为2s22p(2P0)3p和2s22p(2P0)3d, 能级高度介于20 eV和23.6 eV之间。实验还结合时间分辨光谱技术, 对放电等离子体中N2(336.8 nm)、N+(500.5 nm)、N+(399.7 nm)荧光信号进行时间分辨测量。结果表明, N2(336.8 nm)荧光首先出现, N+(500.5 nm、399.7 nm)荧光同时产生, 且滞后N2(336.8 nm)荧光约25 ns。根据时间分辨测量结果和相关参考文献, 文章对放电等离子体中N+的生成通道进行了分析。     

Bi3+掺杂对Sr2MgSi2O7∶Eu2+荧光粉的结构及发光性能的影响

采用溶胶-凝胶法在还原气氛下制备了Sr₂MgSi₂O₇∶Eu²⁺,xBi³⁺(x=0,0.02,0.04,0.06,0.08,0.1)荧光粉,并用XRD、TG-DTA及激发与发射谱仪对样品的结构及发光性能进行了表征。结果发现:单掺杂Bi³⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为286 nm的宽带谱,这是由于激发态时Bi³⁺的³P₁→¹S₀电子能级跃迁而造成的;单掺杂Eu²⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为358 nm的宽带谱,这是典型的Eu²⁺的4f⁶5d¹→4f⁷跃迁而引起的。当Bi³⁺离子掺杂到Sr₂MgSi₂O₇∶Eu²⁺样品的摩尔分数为0.04时,样品的发射强度是未掺杂Bi³⁺离子样品的1.9倍。