Radiative lifetimes of superradiant populated Ba Rydberg levels

Radiative lifetimes of 6s7f¹F₃, as8f¹F₃, and 6s9d¹D₂ Ba Rydberg levels were measured in an atomic beam by time resolved recording of the exponential decay of the fluorescence. The excitation was performed by use of two pulsed dye lasers and a superradiant emission or a superradiant cascade controlled by a cavity.     

OPTICAL ISOTOPE SHIFTS OF Nd II (25524)011/2 USING COLLINEARFAST-ION-BEAM LASER SPECTROSCOPY

Fast-ion-beam laser spectroscopy which has the characteristics of selective excitation and high accurate measurement was widely used to study isotope shifts, radioactive lifetimes, and hyperfine structures of atoms and ions. In this work, the optical isotope shifts for the transition 4f⁴5d⁶K_13/2-(25524)⁰_13/2 in Nd II were measured by using collinear fast-ion-beam lase r spectroscopy.     

Natural radiative lifetimes in the1 P 1 and1 F 3 sequences of Sr I

We have measured radiative lifetimes in the 5s n p ¹ P ₁ (n=5–29) and 5s n f ¹ F ₃ (n=4–11) Rydberg series in neutral strontium. The measurements were performed with single-step laser excitation starting from the ground state or from a metastable state populated by collisions. The decay photons were detected using delayed coincidence technique or a transient recorder. The presence of configuration interaction in the 5s n p ¹ P ₁ series can be observed aroundn=8. The perturbation in the 5s n f ¹ F ₃ series is not reflected in the behaviour of the lifetime values.     

Photoconductivity and photodielectric effect in LiY1 − x Lu x F4 crystals doped with Ce3+ and Yb3+ ions

Time and spectral dependences of the dielectric permittivity of the LiY_{1 ? x} Lu _x F₄ (x = 0, 0.5, and 1) crystals doped with Ce³⁺ and co-doped with Yb³⁺ ions under UV laser excitation were studied by the 8-mm microwave resonant technique at room temperature. The obtained photoconductivity spectrum in 240–310 nm spectral range was interpreted as a stepwise photoionization spectrum of the Ce³⁺ ions due to sequential 4f–5d and 5d–6s transitions. Average lifetimes of free and defect trapped (color centers) charge carriers were estimated.     

The luminescence properties of Eu2+ doped Na2CaMg(PO4)2 phosphor

The blue-emitting phosphors of Eu²⁺-doped Na₂CaMg(PO₄)₂ were prepared by high-temperature solid-state reaction. The crystal phase formation was confirmed by X-ray powder diffraction measurement. The luminescence properties were investigated by photoluminescence excitation and emission spectra. The phosphor exhibited the blue luminescence due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions under the excitation of near UV light. The influence of temperature on the luminescence intensities and decay lifetimes of Eu²⁺ was investigated. An unusual increase of the decay lifetimes of the 4f⁶5d emission of Eu²⁺ ion is observed in Na₂CaMg(PO₄)₂ from 10 K to room temperature. The thermal stability of the luminescence of Eu²⁺-doped Na₂CaMg(PO₄)₂ was discussed.     

The VUV–vis luminescent properties of NaYFPO4: Dy3+ phosphor

Dy³⁺-doped monoclinic NaYFPO₄ phosphor has been synthesized by solid-state reaction technique. Its photoluminescence in the vacuum ultraviolet (VUV)-visible region was investigated. The most intensity broadband emission centered at about 171 nm was the host-related absorption. Another broadband at 153 nm could be related to the O₂→Dy³⁺ charge transfer band (CTB) absorption. The excitation peaks located at 178 nm and 256 nm were the spin-allowed (SA) and spin-forbidden (SF) f–d transitions of Dy³⁺, respectively. Some sharp lines in the range of 280–500 nm were due to the f–f transitions of Dy³⁺ within its 4f⁹ configuration. Under the VUV–vis excitation, the Dy³⁺-doped NaYFPO₄ phosphor showed the characteristic emissions of Dy³⁺ (⁴F_9/2→⁶H_15/2 transitions and ⁴F_9/2→⁶H_13/2 transitions) with a stronger blue emission peaking at about 485 nm. All the chromaticity coordinates of the sample were in the near cold-white region. It can be predicted that this phosphor can be applied in both mercury-free luminescence lamps and white LED.     

Radiative Lifetimes of Some 5d10n2F and 5d10n2P Levels of Hg+

Radiative lifetimes of 8p²P_3/1 (15.3 ns) and nf²F (7f²F_5/2 - 24.7 m. 7f²F_7/2 - 5.5 ns, 8f²F_7/2 - 48.5 ns, 8f²F_5/2 - 47.0 ns) levels of Hg⁺ have been measured employing delayed coincidence method. The dependencies of radiative lifetimes vs effective principal quantum number for np²P_3/2 and np²F_7/2 series are non linear.     

Isotopic shifts and the hyperfine structure of the samarium spectral lines at 672 and 686 nm

Spectra of saturated absorption of Sm atomic vapor from the ground state ⁷ F ₀ and the first even metastable level ⁷ F ₁, ε′=292.58 cm^?1 of the 4f ⁶6s ² configuration to the odd level 4_f ⁶(⁷ F)6s6p(³ P ^o)⁹ F ₁ ^o , ε,=14863.85 cm^?1 were recorded. The lines of the isotopic series were identified, and the hyperfine structure of lines in the spectra of isotopes with a nonzero nuclear spin was determined. The relative isotopic shifts and the hyperfine splitting of the even level 4f ⁶6s ²(⁷ F ₁) were determined.     

Lebensdauern und Oszillatorstärken im Sr I- und Ca I-Spektrum

Radiative lifetimes of some highly excited levels in Sr I were measured by zero-field level crossing technique. These levels have been populated using optical excitation starting from the metastable 4d 5s ¹ D ₂ or 5s5p ³ P _2,1,0 states. The high population of these metastable levels necessary for the experiments was obtained by a discharge in the pure Sr vapour burning in the atomic beam oven. The following lifetimes have been determined (in units of 10^?8 sec):τ(5s 6s³ S ₁)=1.09±0.11,τ(5s 5d ³D₁)=1.67±0.10,τ(5s4f¹ F ₃)=3.43±0.28,τ(4d5p ¹ D ₂)=2.19±0.16,τ(5p ^{2 3}P₁)=0.88±0.12,τ(5p ^{2 3} P ₂)=0.78 _?0.10 ^+0.26 . These results are compared with lifetimes derived from oscillator strengths given in the literature, and the reliability of different oscillator strengths tables is discussed. A corresponding discussion is given for radiative lifetimes of some levels in Ca I published previously. Good agreement with data derived from arc emission oscillator strengths has been found. Ca lifetimes are fairly well consistent with oscillator strengths calculated with semiempirical scaled Thomas-Fermi-wave functions.     

The fluorescence properties of Yb3+ and Er3+ Co-doped YAl3(BO3)4 powders prepared by sol-gel method

Yb³⁺ and Er³⁺ co-doped YAB powders were prepared by sol-gel method. The structure and fluorescence properties were investigated. XRD pattern indicated that the single phase was obtained at 1150°C and the structure belonged to rhombohedral. Under 379 nm excitation, two emissions around 983 nm and 1531 nm were observed and the effect of Yb³⁺ ion concentration on the emission intensity was discussed. The energy transfer was observed under 930 nm excitation and the energy transfer efficiencies for all samples were calculated. The lifetimes of ² F _5/2 level of Yb³⁺ ion and ⁴ I _13/2 level of Er³⁺ ion were measured and the effect of Yb³⁺ ion concentration on the lifetime was also discussed. The results indicated that there was an additional mechanism for the decay of ⁴ I _13/2 level in powder samples. The Yb³⁺ and Er³⁺ co-doped YAB powders should be a potential candidate for ceramic laser materials.     

Determination of natural radiative lifetimes and Landé factors for highly excitedF states in cesium

Natural radiative lifetimes and Landég _J factors for several highly excitedF states in cesium were measured using time-resolved fluorescence spectroscopy. TheF states were excited from the 5² D _5/2 state with a pulse-modulated CW dye laser, and the delayed-coincidence method was employed to record decay curves, which in some experiments exhibited Zeeman quantum beats. A further CW dye laser was used to produce the necessary population in the 5² D _5/2 state. The lifetimes in the sequence 11–16² F _7/2 follow an ^x scaling law withx=2.76 and the Landé factors agree with the predicted value, 1.143.     

Natural radiative lifetimes in the2S1/2 and2D5/2,3/2 sequences of aluminum

Natural radiative lifetimes have been measured for the 3s ² ns ² S _1/2 (n≦10) and 3s ² nd ² D _5/2,3/2 (n≦11) sequences of aluminum using pulsed laser excitation of an atomic beam. The investigated states were populated from the ground configuration using UV pulses of wavelength down to 210 nm produced by a Nd: YAG- or an excimer-pumped dye-laser system. TheS-state lifetimes increase regularily with increasing principal quantum number but this is not the case for theD sequence.     

Experimente mit Erdalkaliatomen in metastabilen Zuständen

An atomic beam source for atoms in metastable states is described. The source was used to produce metastable Ca and Sr atoms in the³ P _0,1,2 and¹ D ₂ and Mg atoms in the³ P _0,1,2 states. The population of these levels was high enough (about 30% of the atoms were in the³ P levels and 3% in the¹ D ₂ level) so that zero field level crossing experiments could be performed at highly excited levels which were populated by an optical excitation starting from the metastable states. The lifetime results obtained for Ca areτ(4s 4d ³ D ₁)=(1.21±0.07)·10^?8sec,τ(4s 4f¹ F ₃)=(2.84±0.23)· 10^?8sec, andτ(3d 4p ¹ F ₃)=(6.15±0.62)·10^?8 sec. The three lifetimes have been evaluated using theg _J values forLS-coupling. The quoted uncertainties include the errors by a possible deviation fromLS-coupling.     

Charge transfer effects on the luminescent properties of Eu3+ in oxysulfides

Energy shifts of 4f⁶ states of Eu³⁺ in matrices, and phonon sidebands, linewidths and luminescence decay of Eu³⁺ in Ln₂O₂S (Ln=Lu, Y, Gd and La) have been studied. The charge transfer state (CTS) of Eu³⁺ is described by a model in which a hole is transferred from Eu³⁺ to ligands. Septet states obtained from the 4f⁷(⁸S) + hole configuration of CTS interact with the ⁷F term of the 4f⁶ configuration. This effect causes downward shifts of ⁷F_J states in matrices. Diffuse charge distributions for ⁷F_J states due to the mixing with CTS make the curvatuve of their adiabatic potential curves be smaller than that for ⁵D_J'. Such a difference in the potential curves between ⁷F_J and ⁵D_J' causes broadening of the absorption lines compared with the corresponding emission linewidths in Y₂O₂S. A dynamic Jahn-Teller model is proposed for the concentration-enhanced phonon sidebands accompanying 4f-4f transitions. The vibronics appear only in the excitation spectra and not in the emission spectra. Spectral distributions of the effective density of phonon states are obtained from the observed phonon sidebands for Ln₂O₂S: 5%Eu. The phonon spectra indicate delocalization of the 4f orbitals of Eu³⁺ with increasing the host-cation radius. The observed lifetimes of ⁵D₀ show a decrease in the same order due to decrease in the 4f-CTS mixing.     

Luminescence study of the 4f5d configuration of Nd in LiYF4, LiLuF4 and BaY2F8 crystals

Ultraviolet fluorescence of Nd³⁺ ions induced by triphotonic excitation process was studied in Nd-doped LiYF₄, LiLuF₄ and BaY₂F₈ crystals using a technique of time-resolved spectroscopy. The observed ultraviolet luminescence was due to transitions between the bottom of 4f²5d configuration and 4f³ states of Nd³⁺ ions. Narrow emission lines superposed to the broadband emissions were observed. A detailed analysis of luminescence spectrum revealed that the narrow emissions are due to parity and spin allowed radiative transitions from the Stark levels of ⁴K_11/2(5d) state created by the electrostatic interaction between the 5d electron and the two electrons of the 4f² configuration. The narrow emissions are related to the high spin state (S=3/2) which gives f-f characteristics to the f-d broadband emissions. The narrow emissions superposed to the wide emission correspond to 18%, 34% and 43% of the integrated broadband emission at 262 nm observed in LiYF₄, LiLuF₄ and BaY₂F₈ crystals, respectively. Although the 5d-4f² interaction is observed to be weaker than 5d-crystal field interaction, it is stronger enough to select only the radiative transitions from 4f²5d configuration to 4f³ states that preserves the total spin S=3/2.     

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.     

Radiative lifetimes and tensor polarizabilities of 1s4f 1 F and 1s5f 1 F level of He I

He atoms have been excited by Ne⁺ ion impact and the depolarization of the fluorescence lines at 668 nm and 492 nm by magnetic and electric fields has been studied. The Ne⁺ ion energy could be chosen such that pure cascade level crossing signals were observed. From the widths of magnetic depolarization signals the radiative lifetimes τ(1s4f ¹ F)=74(2) ns and τ(1s5f ¹ F)=133(5) ns have been determined. By investigating the electric field splitting of the magnetic depolarization signals the tensor polarizabilities ¦α _ten(1s4f ¹ F)¦=0.58(1) kHz/(V/cm)² and ¦α _ten(1s5f ¹ F)¦=4.2(1) kHz/(V/cm)² have been deduced. From the latter value a mean frequencyv(1s5g?1s5f)=14.4 GHz of the transitions between the levels of the 1s5f configuration and those of the 1s5g configuration has been derived.α _ten(1s4f ¹ F) depends sensitively on the singlet-triplet mixing in the 1s4f configuration and thus a mixing coefficient could be deduced for this configuration.     

Luminescent studies of Dy ion in alkali lead tellurofluoroborate glasses

Dy³⁺-doped alkali lead tellurofluoroborate (RLTB) glasses (R=Li, Na and K) were prepared by melt quenching technique. Judd-Ofelt theory has been used to evaluate the three intensity parameters Ω₂, Ω₄ and Ω₆ from the experimental oscillator strengths. The photoluminescence spectra obtained by the excitation wavelength of 385 nm show four emission bands at 454, 483, 575 and 665 nm corresponding to the ⁴I_15/2→⁶H_15/2 and ⁴F_9/2→⁶H_J/2 (J=15/2, 13/2 and 11/2) transitions, respectively. The laser characteristic parameters like fullwidth at half maxima (FWHM), stimulated emission cross-sections (σ_e), optical gain parameters (σ_e×τ_exp) and gain bandwidth parameters (σ_e×FWHM) were determined. From the visible emission spectra, yellow to blue (Y/B) intensity ratios and chromaticity coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state were also measured and discussed.     

Spectroscopic investigations and configuration-interaction-assisted crystal field analysis of Pr in YPO4 single crystal

An optical study of a Y_0.99Pr_0.01PO₄ single crystal is presented. Measurements of optical absorption, excitation, and emission by selective excitation into ¹D₂, ³P₀ and ³P₁, at different temperatures between 20 and 295 K, are described. A detailed account of the line assignments is given for absorption in the 4300-23 000 cm⁻¹ spectral range, and for emission in the 6400-23 000 cm⁻¹ range. The lifetimes of the emitting levels are determined. Vibronic sidebands accompanying absorption, emission and excitation spectra are reported. The decay processes of the ³P₁, ³P₀ and ¹D₂ levels are discussed. The aim of this study is a test of the configuration-interaction-assisted crystal field analysis as well as the accurate experimental determination of the energy level scheme. It was reported previously that the introduction of configuration interaction between the ground 4f² configuration with the excited 4f6p configuration always resulted in a decrease (≈50-60%) in the standard deviations between the observed and calculated energy levels. In the present work the 4f5d configuration is included as well. The crystal field is analysed in the theoretical D_2d site symmetry with and without configuration interaction. The results with 4f², 4f²+4f5d, 4f²+4f6p and 4f²+4f5d+4f6p are given. The calculation on the basis of the 315 (4f²+4f5d+4f6p) levels gives the best overall standard deviation lowering it by 75% with regard to the calculation on the 91 4f² levels only.     

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in ¹⁶⁹Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state 4f¹³6s²(²F₀)(J_g=7/2) to upper states 4f¹²(³H₅)5d_3/26s²(J_e=9/2) at 410.6 nm and 4f¹²(³F₄)5d_5/26s²(J_e=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that the strong transition at 410.6 nm has an optical leak rate of less then 2×10^-5 and can be used for efficient laser cooling of ¹⁶⁹Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s^-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (J_g=7/2)↔(J’_g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks. PACS 32.70.Cs; 32.10.Fn; 32.80.Pj