Investigations of the spin-Hamiltonian parameters for Er3+ ions in AlN crystal

The spin-Hamiltonian parameters (g factor g _//, g _⊥ and hyperfine structure constants A _//, A _⊥) for Er³⁺ ion at the trigonal Al³⁺ site of AlN crystal are calculated by diagonalising the 52 × 52 energy matrix. The matrix are related to the ground mutiplet ⁴I_15/2 and the first to third excited multiplets ⁴I_13/2, ⁴I_11/2 and ⁴I_9/2 for 4f¹¹ ions in trigonal crystal field under an external magnetic field. The crystal-field parameters used in the matrix are obtained from the superposition model and the local lattice relaxation due to the substitution of Er³⁺ for Al³⁺ is considered. The calculated spin-Hamiltonian parameters are in reasonable agreement with the experimental values and the signs of hyperfine structure constants are suggested. The results are discussed.     

Er^3＋：YAG晶体Er^3＋离子的浓度对电磁感应光透明的影响

在一个三能级模型中展示了Er^3 :YAG晶体中的Er^3 浓度对电磁感应光透明（EIT）的影响。没有耦合场时,Er^3 离子浓度在15％左右时吸收达到最大;存在共振耦合场时,Er^3 离子浓度在3％左右时透射有一个最优值。     

Er3+:GdVO4中Er3+离子的光谱参数计算和晶场中能级分裂的讨论

对Er3+:GdVO4样品的光谱参数以及Er3+在晶场中能级的分裂情况进行了研究.首先对样品进行了吸收光谱的测量,接着用Judd-Ofelt理论拟合出了Er3+在GdVO4晶体中的强度参量Ωt,并由此计算了跃迁的振子强度、自发辐射跃迁速率、荧光分支比和积分发射截面.通过计算结果可以发现有较多能级之间的跃迁都有大于10-6的振子强度和大于10-18 cm的积分发射截面,并且具有较高的荧光分支比,特别是2H11/2→4I15/2,4S3/2→4I15/2,4F9/2→4I15/2和4I13/2→4I15/2等几个强发光能级除了具有较大的振子强度和积分发射截面外还有很好的应用前景,因此也更加值得关注.最后还利用群论讨论了Er3+离子在GdVO4晶场中各能级的分裂情况并对各Stark子能级的Jz混杂情况进行了分析.     

Zeeman splitting factor of the Er3+ ion in a crystal field

Numerical computations are presented on the energy levels of the Er³⁺ ion in crystalline fields of cubic, trigonal, tetragonal and orthorhombic symmetry. Zeeman splitting factors were obtained from the level splitting in an additional magnetic field. For the quartet Γ₈ states in cubic symmetry the Zeeman effect is described by an effective Hamiltonian ℋ= gμ_BBJ+ uμ_BBJ³ with the parametersg andu calculated for mixed fourth- and sixth-order potentials. For the eight doublets in the lower symmetry of an axial trigonal or tetragonal crystal field the principalg tensor components g_∥ and g_⊥ were calculated. The results of such calculations for a ground-state doublet can exactly account for the experimental data obtained on around 70 erbium centers in various crystalline hosts. However, sometimes different sets of parameters give comparably good results. An empirical rule of constant trace g_∥ + 2g_⊥ is supported by the calculations. In contrast to analytical treatments the effect of the crystalline field can be followed over a continuous range of the crystal field parameters. This allows one to establish relations on the relative signs of tensor components. It is found that the measured trace of tensors |g_∥| + 2|g_⊥| is not always equal to their real trace g_∥ + 2g_⊥. In an exploratory calculation a nonaxial center was simulated in an orthorhombic field, with calculation of the three principal values g_x, g_y and g_z. A good agreement is obtained for the recently reportedg values of an erbium center in silicon.     

Weak magnetic field behavior of photon echo in a LuLiF4:Er3+ crystal

We report the first observation and study of the photon echo in Er³⁺:LuLiF₄. The energy transition is ⁴ I _15/2 → ⁴ F _9/2 (λ = 6536 Å). The density of ErF₃ is 0.025 wt %. The operation temperature is 1.9 K. Measurements were made at low (up to 1200 Oe) and even zero external magnetic fields. We studied the behavior of the photon echo intensity vs. the magnetic field magnitude and direction about the crystal axis C and vs. the laser pulse separation t ₁₂ and observed an exponential growth and then, after a certain plateau, an exponential decrease in the photon echo intensity as a function of magnetic field upon increasing the magnetic field from zero. The parameters describing the exponential growth and decrease are independent of the direction of magnetic field. The value of the magnetic field (～20–200 Oe) at which the echo intensity is maximal and the value of the maximum itself decrease with increasing pulse separation t ₁₂ and the angle Θ between the magnetic field and crystal axis. The echo intensity decreases exponentially with increasing Θ. The parameter describing the exponential decrease is independent of the magnitude of the field. The echo intensity as a function of pulse separation shows exponential decay. The phase relaxation time depends on the magnitude and direction of the magnetic field. T ₂ is equal to 202 ± 16 ns at zero magnetic field. A phenomenological formula is suggested, which qualitatively presents the mentioned dependences, and the polarization properties of the backward photon echo in this crystal are studied. Because the ion of trivalent erbium is an optimum data carrier, the above results show that fine control of the multichannel transfer of processed optical information may be achieved by weak magnetic fields.     

Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO₃ and Er/Yb:LiNbO₃ crystals were grown by the Czochralski technique. The laser characteristics of 1.54 μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ω_t (Ω₂=7.23×10^?20 cm², Ω₄=3.15×10^?20 cm² and Ω₆=1.43×10^?20 cm²) were obtained. The stimulated emission cross sections (σ_em) at 1.54 μm emission in Zn/Er/Yb:LiNbO₃ were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO₃ crystal was also investigated. Under 980 nm excitation, a lenghthening lifetime of 1.54 μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO₃ crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn²⁺ ion tridoping increases the probability of cross relaxation process between the two neighboring Er³⁺ ions.     

Effect of concentration of the Er3+ ion on electromagnetically induced transparency in Er3+:YAG crystal

We studied the effect of Er³⁺ concentration on electromagnetically induced transparency in two types of three-level schemes—the ladder and the Λ models in Er³⁺:YAG. The numerical calculations show that, under the same intensities of the probe and the coupling fields, the absorption and the dispersion were dramatically changed with Er³⁺ concentration.     

Energy transfer between Yb3+ and Er3+ ions in an Er,Yb:YAl3(BO3)4 crystal

The electron-excitation energy transfer between Er³⁺ and Yb³⁺ ions in Er,Yb:YAl₃(BO₃)₄ crystals has been investigated. Crystals with different concentrations of active ions have been grown, and their luminescence decay kinetics in the spectral range near 1 μm have been experimentally measured. The energy-transfer microparameters have been calculated. It is shown that, to correctly describe the energy transfer in Er,Yb:YAl₃(BO₃)₄ crystals, one must take into account the interactions of higher orders than dipole-dipole interactions.     

Er~(3+)∶YVO_4的频率上转换动力学分析

测量并分析了980nm抽运下Er3+∶YVO4晶体的上转换荧光,建立了描述Er3+离子跃迁的速率方程。通过求解速率方程并拟合1550nm,980nm和550nm的荧光衰减实验曲线,得到了4I13/2+4I13/2→4I15/2+4I9/2,4I11/2+4I11/2→4I15/2+4F7/2的频率上转换系数C22=9.221×10-17cm3s-1,C33=7.545×10-17cm3s-1。通过测量980nm抽运下的550nm荧光衰减谱,得到了4S3/2能级的主要上转换机制是以激发态吸收为主。     

Covalent bonding and J–J mixing effects on the EPR parameters of Er~(3+) ions in GaN crystal

The EPR parameters of trivalent Er~(3+) ions doped in hexagonal Ga N crystal have been studied by diagonalizing the 364×364 complete energy matrices. The results indicate that the resonance ground states may be derived from the Kramers doublet Γ_6. The EPR g-factors may be ascribed to the stronger covalent bonding and nephelauxetic effects compared with other rare-earth doped complexes, as a result of the mismatch of ionic radii of the impurity Er~(3+)ion and the replaced Ga~(3+) ion apart from the intrinsic covalency of host Ga N. Furthermore, the J–J mixing effects on the EPR parameters from the high-lying manifolds have been evaluated. It is found that the dominant J–J mixing contribution is from the manifold ~2K_(15/2), which accounts for about 2.5%. The next important J–J contribution arises from the crystal–field mixture between the ground state ~4I_(15/2) and the first excited state~4I_(13/2), and is usually less than 0.2%. The contributions from the rest states may be ignored.     

Quarkonium production from d + Au to Au + Au collisions

The PHENIX experiment measured J/ production in pp, d + Au and Au + Au reactions at = 200 GeV over a wide range of rapidity and transverse momentum. The nuclear modification factor obtained by comparing the d + Au and pp cross sections as a function of rapidity, is consistent with shadowing of the gluon distribution functions. J/ production in Au + Au collisions was compared to the production in pp collisions and it was found to be inconsistent with models that predict strong enhancement relative to binary collision scaling. Arrival of the final proofs: 29 June 2005 PACS: 25.75-q, 25.75-Dw, ^* Deceased Spokesperson     

Dopant occupancy and optical properties of Er3+ in Er/Zn-codoped lithium niobate crystal

The effect of Zn²⁺ ion on the dopant occupancy and optical characteristic of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal is reported. The intense 1.54 μm and relatively weak green upconversion emissions are observed for Er (1 mol%)/Zn (6 mol%):LiNbO₃ crystal. The OH^? absorption and the time-resolved spectra show that the Zn²⁺ codoping decreases the threshold concentration of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal. The experimental results here imply that the potential application of Er³⁺-doped LiNbO₃ crystal can be designed and optimized on the basis of the theoretical investigations.     

Er3+:YVO4中Er3+的光谱参数计算

根据掺杂Er3+(0.5%)的YVO4样品的吸收光谱,用Jubb-Ofelt理论拟合出唯象强度参最Ωλ,并由此计算了激发能级的振子强度、自发辐射跃迁速率、荧光分支比和积分发射截面等光谱参量.并根据这些光学参量,分析了Er3+:YVO4晶体的应用价值.其中,特别是4I13/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2和4F9/2→4I15/2等几个强发光能级具有较大的振子强度(大于10-6)和积分发射截面(大于10-18cm),分别分析了它们的应用前景,因此非常值得关注.并且,本文结果和Capobianco等所报道的Er3+(2.5 mol%):YVO4晶体强度参量结果很相近.而且,通过比较掺Er3+钒酸钇晶体和掺Er3+其他晶体的光学性能,可以看出钒酸钇晶体作为激光晶体的优点.最后,还根据Er3+在晶体中的对称性,利用群论讨论了Er3+在YVO4晶场中各能级的劈裂情况.     

Intensity parameters of Tm3+ and Er3+ in borate,phosphate and germanate glasses

Intensity parameters τ_λ of the Judd-Ofelt expression were obtained from oscillator strengths of the electronic transitions of Tm³⁺ and Er³⁺ in the visible and infrared part of the spectra. The parameters are interpreted by means of static and dynamic crystal field expansion. The τ_λ 's of Tm³⁺, Er³⁺ and Eu³⁺ are expressed as a function of the h (covalency parameter) parameter of the glass. It is concluded that vibrational interaction plays a dominant role in the origin of the forced electric dipole transitions of Tm³⁺ and Er³⁺ in glasses.     

Luminescence characteristics of ultraviolet upconversion from Er 3 + :YAG crystal by Ar + laser (488 nm) excitation

Ultraviolet and violet upconversion signals at 271 nm, 317 nm, 381 nm and 407 nm were observed when an erbium-doped YAG crystal was pumped by an Ar⁺ laser (488 nm). The dependence of intensity of luminescence emitting from the ⁴S _3/2 state and the ²P _3/2 state on pump power (I) was experimentally investigated. Changes from I¹ down to I ^1/2 for the ⁴S _3/2 state and from I² down to I¹ for the ²P _3/2 state were observed. The upconversion mechanism was discussed by means of the rate equations. It appears that energy-transfer upconversion (ETU) is a dominant process for the Er³⁺:YAG crystal used in our experiment. Received 20 March 2001 and Received in final form 11 July 2001     

VUV-UV-visible luminescence of Nd3+, Er3+ and Tm3+ in LiLuF4 single crystal host

An overlook of absorption and luminescence characteristics of Nd³⁺, Er³⁺ and Tm³⁺ centers in LiLuF₄ single crystal is provided. Single crystal doped with the mentioned RE ions were prepared by micro-pulling-down technique in the form of few cm long rods with the diameter of about 2 mm. Excitation and emission spectra and fast decay kinetics in VUV spectral region were measured at SUPERLUMI station at synchrotron DESY, Hamburg and characterization was further completed in UV-visible region at conventional spectrophotometers. Observed absorption and emission peaks are ascribed to the 5d–4f and 4f–4f optical transitions in the doped rare earth ions. Concentration dependence of the decay kinetics is discussed.     

Er3+-doped phosphor-tellurite glass for broadband short-length Er3+-doped fiber amplifier

ErS+-doped phosphor-tellurite glass for broadband short-length Er3+-doped fiber amplifier (EDFA) is fabricated and characterized. The differential value (△T) of onset crystalline temperature (Tx) and glass transition temperature (Ts) is 206°C.     

Record performance from a Q-switched Er3+:Yb3+:YVO4 laser

A diode-pumped Yb³⁺, Er³⁺:YVO₄ laser was Q-switched by the rotating prism method and record performance obtained. Pulse energies of up to 0.2 mJ and pulse durations as short as 60 ns were demonstrated. A model based on a system of rate equations is also described and used to explain the observed behaviour.