The study of two-color excitation upconversion of Pr(0.5)Yb(3):ZBLAN

The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion excitation transition [¹G₄(Pr³⁺)→¹I₆(Pr³⁺) and ¹G₄(Pr³⁺)→³P₁(Pr³⁺)], the 789.0 nm upconversion excitation transition ¹G₄(Pr³⁺)→³P₂(Pr³⁺), and the 803.7 nm upconversion excitation transition ³H₆(Pr³⁺)→¹D₂(Pr³⁺). The upconversion excitation transition ¹G₄(Pr³⁺)→¹I₆(Pr³⁺) is strong because its oscillator strength f = 23.040×10⁻⁶ is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal light simultaneously.     

Multiphonon relaxation of optical excitations in CsCdBr<Subscript>3</Subscript>:Pr<Superscript>3+</Superscript> and LiYF<Subscript>4</Subscript>:Nd<Superscript>3+</Superscript> crystals

The technique of calculation of the n-phonon transition rates between electronic sublevels of impurity rare earth ions in dielectric crystals is developed in the case when n>2. The n-phonon transition probabilities are calculated according to the 1st and 2nd orders of perturbation theory. The Hamiltonian of the electron-phonon interaction is constructed in the framework of the exchange charge model and developed as series in relative displacements of the rare earth ion and ligands. The contribution of the lattice anharmonicity on the probabilities of n-phonon transitions is taken into account. On the basis of the developed technique, the nonradiative relaxation rates of ⁴ G _7/2 multiplet of Nd³⁺ ions in LiYF₄:Nd³⁺crystal and ³P₁ multiplet of Pr³⁺ ions in CsCdBr₃:Pr³⁺ crystal were computed. The results of our calculations show that the 2nd order terms in the expressions for the probabilities studied here are comparable with, and in some cases prevail over the 1st order terms. An account of lattice anharmonicity in case of LiYF₄:Nd³⁺ crystal substantially modifies the corresponding multiphonon relaxation rates. The calculated nonradiative relaxation rates for both crystals agree well with the experimental data.     

Optical transitions of Pr3+ and Er3+ ions in LiYF4

The optical absorption, emission, and excitation spectra of Pr³⁺ and Er³⁺ ions in LiYF₄ have been measured and energy level schemes established which agree with previous work. The temperature dependence of the emission lifetimes were investigated and analyzed using the Huang-Rhys and Struck-Fonger treatments of multiphonon decay. The non-radiative processes in LiYF₄: Er³⁺ were shown to follow the same “gap law” behavior as Er³⁺ in LaF₃ and MnF₂. Theoretical fits to the Huang-Rhys model allowed the construction of a configuration coordinate diagram for the Er³⁺ system. The non-exponential temperature dependence of the ¹D₂ lifetime in Pr³⁺ can be understood as a non-radiative transition from higher levels.     

Emission centers in Ca1–xPrxF2+x (x = 0.35) solid solutions

Luminescence spectra of Ca_0.65Pr_0.35F_2.35 solid solutions are studied. It is found that, depending on the excitation energy, different kinds of emission centers appear in these spectra. An interconfigurational 4f ¹5d¹ →4f² luminescence is typical for single Pr³⁺ ions in tetragonal sites. Data on the structure of the solid solutions show that the emission centers involved in ¹S₀ → 4f² transitions can be attributed to Pr³⁺ ions contained in clusters.     

Calculation of the probability of the 4 T 2→4 A 2 transition in luminescence spectra of the Mn4+ ion in gadolinium-gallium garnet

The ⁴ T ₂→⁴ A ₂ transition of the Mn⁴⁺ ion has been observed in the luminescence spectrum of Mn⁴⁺:Cd₃Ga₅O₁₂ upon intense laser pumping. It is shown that an increase in the intensity of the ⁴ T ₂→⁴ A ₂ transition with respect to the ² E→ ⁴ A ₂ transition in these crystals with increasing pumping power relates to the increased role of induced transitions. The intensity of this process is greater in the region where the ² E→⁴ A ₂ and ⁴ T ₂→⁴ A ₂ transition bands overlap most, which leads to an increase of the zero-phonon line of the latter transition, peaking at a wavelength of 694 nm. The rates of radiative and nonradiative recombination involving the ⁴ T ₂, ² E, and ⁴ A ₂ terms of the Mn⁴⁺ ion in gallium-gadolinium garnet (GGG) are calculated using data from luminescence spectra measured at different temperatures. The Mn⁴⁺:GGG crystal is proposed for use as an active element of lasers with continuous frequency tuning. __________ Translated from Optika i Spektroskopiya, Vol. 94, No. 4, 2003, pp. 590–596. Original Russian Text Copyright ? 2003 by Bulyarskiĭ, Zhukov, Prikhod’ko.     

Resonant Raman scattering and photochromic effects in KI:MnO 4 −

A study is reported of photoinduced bleaching in the resonant Raman (RR) scattering spectra of KI:MnO ₄ ⁻ crystals under laser excitation of the MnO ₄ ⁻ centers in resonance with the ¹ A ₁→¹ T ₂ optical transition. The bleaching effect is found to exist for all RR lines and is studied in detail as a function of time, temperature, and laser excitation power for the ν ₁ line. A reversible and an irreversible process are observed, whose contributions to the total effect depend on temperature. It is established that the decrease in RR intensity is accompanied by a decrease in integrated impurity absorption. The observed photochromic effects are attributed to photoinduced instability of the MnO ₄ ⁻ ions. The results find qualitative interpretation within a three-center model including the following photoelectronic processes: photothermal ionization of the permanganate, electron ejection from the excited state of the impurity center into the conduction band, and electron capture by traps of two types, with subsequent trap reactivation. The intensity distribution in a multiphonon RR scattering spectrum obtained at 5 K is used to find the main electron-phonon interaction constants. The introduction of the permanganate ion is found to excite a local lattice vibration, which is observed both near the exciting line and in combination with the fully symmetric intramolecular vibration of the impurity ion itself. Fiz. Tverd. Tela (St. Petersburg) 39, 1567–1574 (September 1997)     

Double Fluorescence Conversion in Ultraviolet and Visible Region for Some Praseodymium Complexes of Aromatic Carboxyates

Four praseodymium complexes of aromatic carboxylates (benzoate, 4-tert-butylbenzoate, 2-benzoylbe-noate, and benzimidazole-5-carboxylate) have been synthesized and characterized, whose photophysical properties have been studied with ultraviolet spectra, phosphorescence spectra, and fluorescence spectra. The fluorescent emission spectra of all praseodymium complexes show two emission peaks under the excitation band of 245 nm at about 395 and 595 nm respectively, while one peak under 415 nm at about 595 nm, which attributed to be ¹S₀ → ¹I₆ (395 nm) transition and the characteristic emission ¹D₂ → ³H₄ (595 nm) transition of Pr³⁺ ion. The ¹S₀ → ¹I₆ transition can be ascribed as the transition of charge transfer state, and the ¹D₂ → ³H₄ can be further proved that there exists an antenna effect in the fluorescence of praseodymium with aromatic carboxylic acids. In conclusion, the praseodymium complexes systems can realize the double fluorescent conversion in both ultraviolet and visible region and can be further studied the application of this conversion.     

Pr<Superscript>3+</Superscript>-doped Tl<Subscript>3</Subscript>PbBr<Subscript>5</Subscript>: a non-hygroscopic,non-linear and low-energy phonon single crystal for the mid-infrared laser application

This letter presents the optical and spectroscopic properties of a new low-energy phonon, moisture-resistant and non-linear Pr³⁺:Tl₃PbBr₅ single crystal. Though only weakly doped with Pr³⁺ ions, centimetre-size and good-quality single crystals could be grown and analyzed. Absorption and emission spectra as well as fluorescence kinetics were registered in the mid-infrared spectral domain. Strong luminescence at around 4–5.5 μm was observed and assigned to the ³H₅→³H₄ transition of the Pr³⁺ ions. The high value of the resulting emission cross section associated with the long lifetime of the ³H₅ emitting level indicates that this material could be a good candidate for the development of a broadly tunable mid-infrared solid-state laser source.     

QUANTUM EFFICIENCY AND MULTIPHONON NONRADIATIVE TRANSITION OF Er3+ IONS IN FLUORIDE GLASS

Optical absorption, emission and excitation spectra, lifetimes of ⁴S_3/2 state and ⁴F_9/2 state from 10K to 500K, and Raman spectra were measured for Er³⁺ ions in fluoride glass. The radiative transition probabilities were calculated on the basis of Judd-Ofelt theory. The nonradiative transition probabilities and the quantum efficiencies were determined by calculating the difference between the measured lifetimes and the calculated radiative transition probabilities. The temperature dependence of nonradiative transition provavility was investigated using the Huang-Rhys theory of multiphonon relaxation , in which two kinds of phonons as well as the parameter s were taken into consideration. A fairly good agreement of the theoretical calculation with the experimental results has been obtained. The value of s is estimated and the effect of s is discussed.     

Upconversion excitations in Pr<Superscript>3+</Superscript>-doped BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystal

We report the orange-to-blue and infrared-(IR)-to-blue wavelengths upconversion luminescence in Pr³⁺:BaY₂F₈ crystals. Mechanism of the orange light upconversion into blue ³P₀ state emission was confirmed to be energy transfer between two Pr³⁺ ions in the ¹D₂ state. IR-to-blue upconversion has only been observed under two different color IR pumping. The first resonant step was the ³H₄→¹G₄ ground state absorption transition, and the second resonant transition was the excited state absorption from the ¹G₄ to ¹I₆ and ³P_J levels. A comparison of the efficiency of the IR-to-blue upconversion in several praseodymium activated host is presented and discussed. A model of the IR pumped upconversion praseodymium blue laser is presented and the population inversion conditions are calculated.     

晶格弛豫和多声子跃迁理论

近年的发展日益证明,固体中的局域电子态所导致的晶格弛豫(晶格原子位置移动)是局域电子态的一项基本特征,能够引起许多重要的效应。在局域态的吸收和发射光谱中,由于晶格弛豫而引起斯托克斯位移和光谱的多声子结构(多声子的光跃迁)。晶格弛豫又可以在不同电子态之间引起无辐射跃迁,其中的能量变化完全由多声子的发射或吸收来补偿(多声子无辐射跃迁)。本文以线性的电子—声子作用和简谐近似的晶格模型为基础,系统地总结阐明多声子的光跃迁理论和多声子的无辐射跃迁理论。关于光跃迁的部份既介绍了直接计算跃迁几率的方法,也介绍了采用傅里叶变换的理论,并分析了连续谱和多声子结构相互叠加的一个光谱实例。关于无辐射跃迁的部份着重分析和澄清了多年来环绕所谓“康登近似”出现的矛盾,从而把近年来不同的理论发展置于统一的基础之上。介绍了估算跃迁几率的最陡下降法。最后讨论了强耦合和弱耦合的情形。     

Photoluminescence Enhancement Effect of CeO2 in Rare Earth Composites MM′O3/CeO2 and MM′O3/CeO2: Pr3+ (M = Ca, Sr; M′ = Ti, Zr)

In the context, a modified sol-gel technology was afford to the synthesis of rare earth composite ceramic phosphors MM′O₃/CeO₂ and MM′O₃/CeO₂: Pr³⁺ (M = Ca, Sr; M′ = Ti, Zr) with multicomponent hybrid precursors were composed. The micromorphology, particle size and photoluminescence properties were studied with XRD, SEM and luminescent spectroscopy in detail. Both XRD and SEM indicated the particle sizes were in the submicrometer range of 100 ∼ 300 nm. The photoluminescence for these ceramic phosphors were studied in details with the different component of host (molecular ratio of Sr, Ca and Ti, Zr), presenting a broad spectral band in the visible blue-violet region with the maximum excitation peak at 449 nm and a wide emission range with a maximum peak at 619 nm, which was ascribed to be the characteristic transition of Pr³⁺ (¹D₂ → ³H₄). These phosphors can be expected for visible light conversion (blue → red) materials. Especially it can be found that the introduction of CeO₂ can enhance the luminescence intensity of MM′O₃ and MM′O₃: Pr³⁺.     

Optical observation of the kinetics of thermalization between the P0 and P1 excited states of Pr in symmetrical Pr-Gd pairs in CsCdBr3

The time dependence of thermalization between the ³P₀ and ³P₁ electronic states of Pr³⁺ in symmetrical Pr³⁺-Gd³⁺ pairs in CsCdBr₃, following pulsed laser excitation into either state, is reflected in the time dependence of the luminescence from both states. The ³P₀ and ³P₁ states achieve thermal equilibrium in the microsecond time domain over the temperature range of study (215-340 K). Because the ³P₀-³P₁ energy gap is larger than the phonon cutoff in CsCdBr₃, thermalization occurs via multiphonon processes. A rate-equation model for the thermalization process is presented, and the temperature dependence of the rate constants for ³P₁←³P₀ multiphonon absorption and ³P₁→³P₀ multiphonon emission is reported from 215-340 K. In contrast to CsCdBr₃, the analogous thermalization kinetics in Pr³⁺-Gd³⁺ pairs in isostructural CsMgCl₃ is not discernable in the ³P₀ and ³P₁ luminescence, because thermalization is instantaneous within the time resolution of our experiments (∼20 ns). The difference in the thermalization kinetics in the two lattices is attributed to the difference in the number of phonons required to bridge the ³P₀-³P₁ energy gap.     

Stimulated emission and radiative properties of Nd ions in barium fluorophosphate glass containing sulphate

Spectroscopic properties of Nd³⁺ in barium fluorophosphate glassy matrix containing sulphate have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. Various spectroscopic parameters viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross sections and optical gain of the principal fluorescence transition from the ⁴F_3/2 metastable level are obtained. Results show that addition of sulphate to the fluorophosphate matrix will enhance the fluorescence spectral properties of Nd³⁺ considerably. Quantum efficiency of the ⁴F_3/2 emission is found to be higher than that of fluorophosphate glasses and stimulated emission cross section of the ⁴F_3/2→⁴I_11/2 transition is the highest among all reported values. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content was carried out and the results show that the water content is below the critical level for optimum laser performance.     

YAG:Pr3+的真空紫外光谱分析及其4f5d能级的研究

用共沉淀法制备出不同掺杂浓度的钇铝石榴石(Y₃Al₅O_{12，YAG)：Pr³⁺粉末.在不同温度下用同步辐射的真空紫外光(VUV)作为激发光 源测量了其发射和激发光谱.对YAG：Pr³⁺被VUV激发后的发光过程进行了分析， 并估算了YAG：Pr³⁺的声子能量、黄昆因子S及Stokes位移.当用170nm光激发样 品时，可能存在自陷激子和通过自陷激子能量传递引发的³P0发射 ，这种跃迁途径不同于用240nm和289nm两个波长激发后的跃迁途径；对Pr³⁺在Y AG中的4f5d能级进行了研究，从而对其4f5d组态有了一个较清晰的认识. 关键词： 3+')" href="#">YAG：Pr³⁺ 同步辐射 4f5d能级 VUV}     

Fluorescence decay dynamics and anneal effect on praseodymium ions doped in lead tungstate single crystal

Fluorescence decay dynamics of main emission manifolds of trivalent praseodymium ions doped in the as-grown and annealed PbWO₄ crystals were analyzed in detail. The fluorescence lifetimes of the ³P₀ and ¹D₂ manifolds were obtained from the fluorescence decay curves measured at room temperature. The main mechanism of fluorescence quenching of the ³P₀ manifold is the non-radiative relaxation to the defect centers coming into being during crystal growth. The dominant non-radiative relaxation for the ¹D₂ manifold is the cross-relaxation energy transfer involving the ¹G₄ and ³F₄ manifolds. The Inokuti–Hirayama model was used to analyze the decay dynamics of the ¹D₂ manifold, and the fluorescence lifetime τ₀ of the as-grown and annealed Pr³⁺:PbWO₄ crystals in absence of cross-relaxation energy transfer are derived as 35.2 μs and 37.9 μs, respectively. The annealing treatment can eliminate most defect centers except for those related to the lead vacancies.     

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.     

Nonlinear absorption properties of Co2+:MgAl2O4 crystal

The differential absorption spectra of Co²⁺: MgAl₂O₄ (MALO) crystal were studied with a picosecond pump-probe technique under excitation of the ⁴A₂→⁴T₁(⁴P) and ⁴A₂→⁴T₁(⁴F) transitions of the tetrahedral Co²⁺ ion. The difference spectra of stimulated emission (SE) and excited state absorption (ESA) were derived from the measured differential absorption spectra. The ⁴T₁(⁴P)→⁴A₂ SE band around 660 nm was observed. The ESA bands were assigned to the ⁴T₂→⁴T₁(⁴P) transition and to transitions from the thermally populated ²E(²G) excited state to doublet levels arising from the ²F free-ion level of the tetrahedrally coordinated Co²⁺ ion. Absorption saturation measurements were performed at 1.34 μm and 1.54 μm. Passive Q-switching of 1.34-μm Nd³⁺:YAlO₃ and 1.54-μm Er³⁺:glass lasers was realized using the Co²⁺:MALO crystal as saturable absorber. The Q-switched laser pulses of 38 ns (110 ns) in duration and up to 2.7 mJ (10 mJ) in energy at 1.54 μm (1.34 μm) were obtained. Received: 3 March 1999 / Revised version: 30 June 1999 / Published online: 30 November 1999     

Charged Higgs bosons in the next-to MSSM (NMSSM)

The charged Higgs boson decays H^±→W^±A₁ and H^±→W^±H_i are studied in the framework of the next-to-minimal supersymmetric standard model (NMSSM). It is found that the decay rate for H^±→W^±A₁ can exceed the rates for the τ^±ν and tb channels both below and above the top–bottom threshold. The dominance of H^±→W^±A₁ is most readily achieved when A₁ has a large doublet component and small mass. We also study the production process pp→H^±A₁ at the LHC followed by the decay H^±→W^±A₁, which leads to the signature W^±A₁A₁. We suggest that pp→H^±A₁ is a promising discovery channel for a light charged Higgs boson in the NMSSM with small or moderate tanβ and dominant decay mode H^±→W^±A₁. This W^±A₁A₁ signature can also arise from the Higgsstrahlung process pp→W^±H₁ followed by the decay H₁→A₁A₁. It is shown that there exist regions of parameter space where these processes can have comparable cross sections and we suggest that their respective signals can be distinguished at the LHC by using appropriate reconstruction methods. PACS  12.60.Fr; 14.80.Cp     

Spectral-kinetic characteristics of Pr luminescence in LiLuF4 host upon excitation in the UV-VUV range

Spectral-kinetic study of Pr³⁺ luminescence has been performed for LiLuF₄:Pr(0.1 mol%) single crystal upon the excitation within 5-12 eV range at T=8 K. The fine-structure of Pr³⁺ 4f ²→4f 5d excitation spectra is shown for LiLuF₄:Pr(0.1 mol%) to be affected by the efficient absorption transitions of Pr³⁺ ions into 4f 5d involving 4f ¹ core in the ground state. Favourable conditions have been revealed in LiLuF₄:Pr(0.1 mol%) for the transformation of UV-VUV excitation quanta into the visible range. Lightly doped LiLuF₄:Pr crystals are considered as the promising luminescent materials possessing the efficient Pr³⁺³P₀ visible emission upon UV-VUV excitation. The mechanism of energy transfer between Lu³⁺ host ion and Pr³⁺ impurity is discussed.