Lifetimes Of Levels Research Articles

Enhanced blue and broadband near-infrared emission of Pr3+/Yb3+ co-doped PbF2 single crystal

High quality Pr3+ single-doped PbF2 and Pr3+/Yb3+ co-doped PbF2 single crystals were grown by temperature gradient technique (TGT). By co-doping Yb3+ ion as Pr3+ ions sensitizer, the visible light emission can be regulated and the largest luminescence branching ratio can be switched from red-orange to blue-green light. Besides, when Pr3+ ions doping concentration is as low as possible, the blue light self-absorption effect can be weakened, which is beneficial to high-efficiency blue laser output. Moreover, the broad band emission around 1.3 μm from 1G4 energy level can be observed in the Pr3+/Yb3+:PbF2 crystal with the low maximum phonon energy for the first time. Absorption, emission spectra and luminescence mechanism are well analyzed by the energy transfer process and J-O theory. The laser upper energy level lifetime of Pr3+ ions has a great increase by Yb3+ ion effect. These advantageous spectroscopic characteristics show that the Pr3+/Yb3+:PbF2 crystal might be potential laser gain materials for blue-green and ∼1.3 μm near-IR laser operation.

Lifetime measurements in 80Br and a new region for observation of chiral electromagnetic selection rules

Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

Solution of the Bateman Equations for Two Identical Decay Constants in the Cascade and Propagation of the Effect Down the Level Scheme

A solution of the Bateman equations for two identical decay constants (λj = λm) of levels in the cascade is proposed. The solution involves a complementary multiplicative linear dependence on time. This solution is the convergence limit of the population function of the lower level m when λj → λm. It represents an additional tool for dealing with specific cases. The propagation of the effect down the level scheme is investigated but no further complications in the functional time-dependence exist. Lifetimes of levels with not completely known feeding history are suggested to be more reliably determined by the method of the moments (expectation values, centroids) than by data fitting.

(Invited) Ultrafast Formation of Long-Lived Charge-Separated State at High Energy Level By Two-Photon Ionization

Photoinduced electron transfer reactions play an important role in various photo-energy conversion processes. A key transient species enabling these processes is the charge-separated (CS) state produced by electron transfer, and its large formation rate constant, high energy level and long lifetime are required for its efficient utilization to the subsequent energy conversion and photoredox reactions. However, the formation rate constant is mutually correlated with the energy gap of electron transfer reactions, and it is difficult to optimize these parameters simultaneously, as shown by the Marcus theory and experimental investigations accumulated to date. In the present study, to create the CS state with the large formation rate, high energy level and long lifetime, we experimentally demonstrated an electron transfer reaction driven by two-photon ionization using a model system of pyrene (Py) as an electron donor and biphenyl (BP) as an acceptor. Photoionization enables ultrafast electron ejection from the donor to the acceptor which is 3-4 nm away from the donor. This long interionic distance effectively inhibits the geminate recombination, and the high energy level of the produced CS state is realized thanks to total energy of two photonsWe first investigated two-photon ionization of pyrene in the absence of the electron acceptor. Photoinduced dynamics of pyrene in acetonitrile solution was investigated under various excitation intensities using transient absorption spectroscopy. Upon photoexcitation at 355 nm, the absorption band at 445 nm, which is ascribable to the radical cation of pyrene, was observed with the S1 state absorption under higher excitation power, while only the S1 absorption appears at low intensities. This result shows that pyrene is ionized by the multiphoton process. Furthermore, the excitation power dependence of this ionization was simulated by a numerical simulation to quantitatively analyze the ionization quantum yield in higher excited state. The absorption signal intensities of the S1 state and radical cation were reproduced by the simulation, and the ionization yield was estimated to be 0.20.The excitation wavelength effect on the ionization was also investigated for optimization of the condition to produce the radical cation. The ionization dynamics was systematically measured by photoexcitation at 340, 355 and 370 nm. The absorption peak due to the radical cation is scarcely seen under 340 nm excitation condition. Under the 370 nm excitation, on the other hand, the quantity of the produced radical cation was maximized among the three conditions. This difference can be interpreted by distinct resonance of the excitation wavelength with the S1-S0 absorption. That is, under 370 and 355 nm excitation where the molar absorption coefficients were respectively 180 and 340 M-1cm-1, the S1 state produced by the first photon absorption can further absorbs the second photon in the excitation pulse. However, under 340 nm excitation at which the absorption coefficient is 4600 M-1cm-1, the second photon absorption by the S1 state is inhibited by the large absorption of the major remaining ground state molecules, which behaves as an intrinsic filter to hide the Sn-S1 absorption. Thus, the stepwise two-photon excitation does not effectively proceed under this condition. Taken together, the photoexcitation at the wavelength region, where the ground state absorption is not prominent, is crucial for efficient ionization driven by stepwise two-photon excitation.We finally performed the proof-of-concept experiments on two-photon ionization-driven electron transfer of the pyrene-biphenyl system. Under the intense excitation condition optimized above, pyrene was excited in a two-photon manner, which can be confirmed by the instantaneous appearance of the radical cation. Other absorption bands show up around 400 and 640 nm in a few tens of picoseconds. These bands are attributable to the radical anion of biphenyl. A detailed global analysis revealed that the anion radical is produced with a time constant of 200 fs, which is followed by vibrational cooling of the resultant ion radicals and the S1 state with a time constant of 16 ps. This observation demonstrates that an electron ejected from pyrene is directly captured by biphenyl on an ultrafast timescale. The energy level of the CS state thus formed was estimated to be higher than that of the S1 state of pyrene by 0.53 eV, which is also confirmed by non-quenching behavior of pyrene fluorescence by biphenyl. In addition, the subsequent ionic dissociation without a remarkable geminate recombination in the sub-nanosecond to nanosecond time region effectively avoids the quantity loss of the CS state. The results in the present work show that two-photon excitation method enables ultrafast formation of the long-lived CS state at a high energy beyond the traditional framework of electron transfer reactions. Figure 1

Radiative Lifetimes for the A and C1Σ+ States of the (SrK)+ Ion Molecular

We have investigated, in a previous work, the transition dipole moments (TDM) of the 13 1Σ+ states of the (SrK)+ molecular ion by using the ab initio method based on the pseudo-potential approach. The radiative lifetimes for all vibrational levels of A and C1Σ+ have been calculated by using such transition dipole moments curves. We have included the bound-free emissions probabilities further to the bound–bound transitions. The bound-free emissions probabilities have been determined exactly, using the Franck–Condon approach, and then included in the total radiative lifetime. An important change has been observed for the higher excited vibrational levels in these lifetimes when the approximate evaluation breaks down. For the first time, the radiative lifetimes associated with the Aand C1Σ+ excited state have been studied here.

Intense 2.9 µm mid-infrared emission from Dy3+/Yb3+：SrF2 crystal under 975 nm excitation

The intense 2.9 µm MIR (mid-infrared) luminescence corresponding to the Dy 3+ : 6 H 13/2 → 6 H 15/2 transition was achieved for the first time in Dy 3+ /Yb 3+ ions co-doped SrF 2 crystals. 2 at% Dy 3+ : SrF 2 ，2 at% Dy 3+ /5 at% Yb 3+ : SrF 2 , and 5 at% Yb 3+ : SrF 2 crystals were grown by Bridgman method. The influence of Yb 3+ on its spectral properties and energy transfer mechanisms has been studied. In comparison to Dy 3+ doped SrF 2 crystals, Dy 3+ /Yb 3+ co-doped crystals exhibit not only intense 2.9 µm emission but also longer high laser energy level lifetimes, favoring 2.9 µm population inversion and lasing behavior. Furthermore, the ET efficiency from Yb 3+ to Dy 3+ in Dy 3+ /Yb 3+ co-doped crystals is found to be as high as 95.34%, indicating that the ET from Yb 3+ is efficient. The results show that incorporating Yb 3+ into Dy 3+ : SrF 2 crystals improves the ability to achieve 2.9 µm lasing action, which could be used as a potential gain media for laser diode-pumped MIR lasers. • The Dy 3+ , Dy 3+ /Yb 3+ and Yb 3+ doped SrF 2 single crystals were grown by the Bridgman-Stockbarger method. • Intense 2.9 µm mid-infrared emission is observed in Dy 3+ /Yb 3+ : SrF 2 crystal under 975 nm excitation. • Detailed spectroscopic properties and energy transfer mechanisms were studied. • Dy 3+ / Yb 3+ : SrF 2 crystals are expected to achieve mid-infrared laser output.

Microstructure and laser emission of Yb:CaF2 transparent ceramics fabricated by air pre-sintering and hot isostatic pressing

Transparent ytterbium doped calcium-fluoride (Yb:CaF2) ceramics were successfully fabricated by air pre-sintering and hot isostatic pressing (HIP) post-treatment from the powders synthesized by the co-precipitation method. The influence of pre-sintering temperature on the densification, microstructures and optical quality of 5 at.% Yb:CaF2 ceramics was systematically investigated. The ceramic sample pre-sintered at 650 °C for 2 h and HIP post-treated at 650 °C for 1 h shows the best transparency with the in-line transmittance of 90% at 1200 nm. The upper level lifetime of the Yb3+ in Yb:CaF2 ceramics was evaluated to be 1.95 ms by the pinhole method. In addition, the laser emission from an optimized 5 at.% Yb:CaF2 ceramic sample yields in the maximum output power of 0.81 W with a maximum slope efficiency of 22.6% at 1028.5 nm under quasi-CW pumping.

Probing the Atomic Structure of Californium by Resonance Ionization Spectroscopy

The atomic structure of californium is probed by two-step resonance ionization spectroscopy. Using samples with a total amount of about 2×1010 Cf atoms (ca. 8.3 pg), ground-state transitions as well as transitions to high-lying Rydberg states and auto-ionizing states above the ionization potential are investigated and the lifetimes of various atomic levels are measured. These investigations lead to the identification of efficient ionization schemes, important for trace analysis and nuclear structure investigations. Most of the measurements are conducted on 250Cf. In addition, the isotope shift of the isotopic chain 249−252Cf is measured for one transition. The identification and analysis of Rydberg series enables the determination of the first ionization potential of californium to EIP=50,666.76(5)cm−1. This is about a factor of 20 more precise than the current literature value.

Insights into the aftereffects phenomenon in solids based on DFT and time-differential perturbed γ−γ angular correlation studies in 111In (→ 111Cd) -doped tin oxides

Recently, a model based on a combined ab initio/time-differential perturbed $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ angular correlation (TDPAC) study in the $^{111}\mathrm{In}(\ensuremath{\rightarrow}^{111}\mathrm{Cd})$-doped ${\mathrm{SnO}}_{2}$ semiconductor was proposed to enlighten the origin of the dynamic hyperfine interactions (HFIs) observed in oxides after the electron-capture (EC) decay of the probe nucleus of the $^{111}\mathrm{In}$ parent. It was demonstrated that both the EC as well as the acceptor level introduced by the Cd impurity can contribute to the variation of the electric-field gradient (EFG) at the Cd site (responsible for this phenomenon) due to charge fluctuations of the electronic holes created [Darriba et al., J. Phys. Chem. C 122, 17423 (2018)]. To disentangle both effects, we performed here TDPAC reversible experiments in $^{111}\mathrm{In}(\ensuremath{\rightarrow}^{111}\mathrm{Cd})$-doped SnO in the temperature range 20--900 K and a complete electronic structure density functional theory study of the Cd-doped SnO system as a function of the charge state $(q)$ of the impurity. The isovalent $^{111}\mathrm{Cd}$ probe impurity in this isocationic oxide was selected to demonstrate that the acceptor character of the probe is not a necessary condition to observe this electronic phenomenon when the EC is already present. A majority fraction of probes sensed a time-dependent HFI (HFI1) for all temperatures, and the unexpected minority always sensed a static interaction (HFI2). Comparing results from these experiments, the ab initio calculations of the EFG tensor and defect formation energies, HFI1 and HFI2, were assigned to $^{111}\mathrm{Cd}$ probes localized at substitutional Sn sites free of defects [with the valence band (VB) completely filled, $q=0$] and with an electronic hole trapped $(q=1+)$, respectively. In addition, we show that the systems with charge state between these values have very similar formation energies at the top of the VB and different predicted EFGs, giving support from first principles to the existence of random fluctuations between different EFGs, necessary in the construction of the on-off perturbation factor used. We demonstrate that all the probes fill their electronic holes before the TDPAC time window except the outermost one, giving a quantification of the number of electronic holes involved in the production of the dynamic effect, only one in SnO. The probes related to HFI2 reach their stable electronic configuration $(q=1+)$ before the emission of the first \ensuremath{\gamma} ray $({\ensuremath{\gamma}}_{1})$ of the \ensuremath{\gamma}-\ensuremath{\gamma} cascade, while those related to HFI1 fill the last hole after the emission of ${\ensuremath{\gamma}}_{1}$, producing the dynamic interaction. Enlighted by these results and reviewing TDPAC experiments from the literature using probes with different nuclear decay characteristics, we concluded that, in the absence of EC decay of the probe nucleus of the parent, any probe impurity introducing acceptor or donor states (in semiconductors and insulators) whose ionization changes the EFG should observe a time-dependent HFI provided the lifetime of the nuclear levels that feed the ${\ensuremath{\gamma}}_{1}$ level and this level itself is shorter than the lifetime of the recovery process (i.e., the lifetime of the electronic holes or the ionized donor electrons).

Spatial modulation spectroscopy of semiconductors using dynamic gratings

Subject of study. Several characterization methods that utilize recording and reading out of dynamic gratings to analyze functional materials are proposed. Method. The methods are based on pulsed recording of thin and volume dynamic gratings followed by reconstruction using continuous laser emission to facilitate the detection of the formation and relaxation dynamics of the recorded diffraction grating. Nonlinear optical, thermo-optic, and kinetic properties of condensed media were obtained based on the measured kinetics of the diffracted signals. Main results. The performance characteristics of a dynamic grating method were analyzed for characterization and parameter measurements of functional materials. In particular, the efficacy of the measurement of the kinetic properties for pulsed recordings of thin and volume holographic gratings was demonstrated. The lifetimes of the short- and long-lived trap levels involved in recording of the dynamic grating were determined in a photorefractive bismuth silicate crystal and the dependence of the diffraction efficiency of the gratings on the intensity of the recording radiation was determined. The advantages of using an additional grating (homodyne) to enable the separation of the contributions of different simultaneously manifesting nonlinearity mechanisms were demonstrated. This method was applied to monocrystalline germanium. A method for assessing the thickness of a film on the surface of a sample based on the amplitude of an oscillating component related to a sound wave propagating in air in the vicinity of the film’s surface was also proposed. A silicon dioxide film was considered as an example. The application of the diffraction to different orders on volume dynamic gratings was proposed for the measurement of the nonlinear optical susceptibility of the fifth and higher orders. The proposed approach was evaluated on photorefractive crystals and semiconductor media. The kinetic and thermo-optic properties, including the time of the population of trap levels, thermo-optic coefficient, and thermal diffusivity, of the media were determined. Practical significance. The proposed characterization methods facilitate the isolation of different nonlinearity mechanisms involved in the formation of dynamic gratings and the measurement of nonlinear optical, thermo-optic, and kinetic properties (optical susceptibilities of different orders, thermo-optic coefficient, thermal diffusivity, and lifetimes of free-charge carriers and trap levels).

Spectroscopic properties of the low-lying states of the HeH radical

Four lowest electronic states ( X2Σ+, A2Σ+, B2Π, and C2Σ+) of the HeH radical are investigated by performing high-precision ab initio calculations. Potential energy curves of HeH are calculated using the multireference configuration interaction method and the basis set of aug-cc-pV6Z. Additional Rydberg basis functions and the Pople correction are included in the calculations. The spectral parameters are evaluated and compared with literature data. The spin–orbit coupling effect of B2Π is taken into account by using the Breit–Pauli operator. Transition dipole moments between those four electronic states are also derived to obtain their emission spectra and radiative lifetimes. Radiative and predissociation lifetimes of several vibrational levels are also calculated, including the bound–continuum and bound–bound systems. Especially, the predissociation lifetimes are elaborated in detail. The results are in good agreement with the reported ones. Additionally, the emission spectra of bound A2Σ+, B2Π, and C2Σ+ states to continuum X2Σ+ state are simulated at different temperatures.

Physical properties and luminescence of highly stable erbium-doped antimony glasses for NIR broadband amplification

Glasses with compositions (0.8-x)Sb2O3−0.2Na2O-(x)WO3-(0.0025) Er2O3, (0 ≤ x ≤ 0.4 mol) has been synthesized by the melt-quenching technique. Physical, optical characteristics and spectroscopy have been identified and investigated. As the glass composition changes, definite variations in physio-optical properties can be observed as well as the temperature of the glass transition (Tg), the density (ρ), molar volume (Vm), bandgap energy (Eg), and the refractive index (n). The Judd-Ofelt theory has been performed using a UV–VIS-NIR absorption spectrum to examine the compositional effect on Er3+ spectroscopic properties. Some basic spectroscopic parameters including electric dipole line strengths, Judd-Ofelt parameters, the rate of radiative probability, and the lifetime of radiative levels, are determined. A high NIR emission at 1.53 μm was observed when exciting glasses at 980 nm. The FWHM, the effective line-width (Δλeff), the emission cross-section (σem), and the gain bandwidth values were calculated using the theory of Füchtbauer–Ladenburg, and the findings were critically analyzed. the decay of fluorescence spectra for the 4I13/2 level was registered, and the lifetime for the studied glasses was calculated. Upconversion luminescence was observed in the green and red regions under 980 nm excitation, with a relative increase in emission intensity due to the added tungsten content. Based on the results obtained, the studied glasses are favorable materials for broadband amplifiers in WDM systems and optical devices.

Spectroscopic and optical investigations on Er3+ ions doped alkali cadmium phosphate glasses for laser applications

Alkali cadmium phosphate glasses doped with erbium ions were prepared by traditional melt - quenching technique. The FTIR and Raman spectroscopies were performed and employed to investigate the structural changes of the glass network doped with different concentrations of Er3+ ions. The UV–Vis–NIR spectroscopy was used to investigate the optical absorption spectra, optical bandgaps, refractive indices, and related parameters. The Judd – Ofelt (J – O) theory was used to explain the structural changes and to determine the bonds nature in the studied glasses by calculating the intensity parameters Ω2, Ω4, and Ω6. The J – O intensity parameters followed the trend of Ω2 > Ω6 > Ω4 and were used to evaluate some radiative parameters such as electric and magnetic radiative transition probabilities, branching ratios, and radiative lifetimes for the excited levels of the Er3+ ions. The absorption and emission cross-sections for the 4I13/2 → 4I15/2 transition of Er3+ ions were studied, and the gain coefficient was calculated. The higher values of the branching ratios (≥ 0.5) and lifetimes of the present glasses indicate their good suitability for lasers and amplifiers applications.

Structural evolution and K mixing in V49

Lifetimes of a few negative parity levels and multipole mixing ratios ($\ensuremath{\delta}$) for a few dipole transitions in $^{49}\mathrm{V}$, populated through the $^{48}\mathrm{Ti}(^{4}\mathrm{He},2np)^{49}\mathrm{V}$ reaction with a 48 MeV $^{4}\mathrm{He}$ beam, were measured. The Indian National Gamma Array (INGA) facility was used to detect $\ensuremath{\gamma}$ rays at three different angles. Large basis shell model calculations were performed to understand the microscopic origin of these levels and to interpret the observations. $K$ mixing between different $K$ bands in $^{49}\mathrm{V}$ were established from one-nucleon-transfer spectroscopic factor calculations and total Routhian surface (TRS) calculations.

Er<sup>3+</sup>,Yb<sup>3+</sup>:YGdSiO<sub>5</sub> Crystal as Gain Media for Lasers Emitting in the Spectral Range of 1.5–1.6 µm

Solid-state erbium lasers, emitting in the spectral range of 1.5–1.6 µm, are of great interest for several industrial applications. Nowadays the Er:glass is the most widespread laser material for obtaining laser radiation at the wavelength near 1.5 µm. However, the maximal output powers of such lasers are restricted by hundreds of milliwatts because low thermal characteristics of the glass host. By this reason the search for new crystalline hosts doped with erbium ions is the actual task.In this article the investigation results of spectroscopic properties of Er3+,Yb3+:YGdSiO5 (YGSO) crystals are reported. Polarized absorption and luminescence spectra were measured. The lifetimes of energy levels were determined. The excited state absorption spectra were measured. It was shown that excited state absorption band does not overlap with gain band in the range 1.5–1.6 µm. The energy transfer efficiency from ytterbium to erbium ions was estimated. The stimulated emission and gain cross-section spectra for Er3+ ions in YGSO were calculated.

Er3+-doped LuYSGG crystal as a potential 2.79 μm radiation-resistant laser material

We demonstrate the influence of gamma-ray irradiation on the structure, spectroscopies, and laser performance of Er:LuYSGG crystal. After 100 Mrad 60Co gamma-ray irradiation, the crystal structure remains unchanged, the absorption near 968 nm and emission within 2.7 ∼ 3 μm are almost unaffected, the level lifetimes are reduced, and the maximum output power of 886 mW is achieved with a maximum slope efficiency of 20.8%. The maximum output power and slope efficiency decrease by only 2.5% and 3.7% after irradiation, respectively, and the M2 factor is little affected by irradiation. The results indicate that the Er:LuYSGG crystal is a potential mid-infrared radiation-resistant laser material applied in radiation environments.

Устойчивость процедуры вычисления радиационных времен жизни

Purpose: Radiation lifetimes of atom and ion energy levels refer to fundamental physical constants which knowledge of is necessary in many fields of both, fundamental or applied science. The knowledge of these values is necessary at search of active medias for optical generators, for plasma both laboratory or astrophysical and other diagnostics. While lifetime calculation, it’s very vital to evaluate the impact of simplifications and supposition, put on the basis of calculation procedure. In particular, to evaluate impact of configuration superposition which consideration significantly complicates calculation model. The present work investigates this issue on a particular example of spectrum of sixfold wolfram ion W VII. Methods: Superposition of configurations 4f 13 5p6 6p + 4f 14 5p5 6p in the spectrum of erbium-similar W VII is investigated by semiempirical method of intermediate coupling with the use of energy experimental levels known from the literature. Together, wave functions of intermediate binding of odd configurations have been found in a single-configuration approximation; radial integrals, that’re necessary for transfer to absolute scale of transition probabilities, are calculated in the form of length with Hartree-Fock functions. Lifetimes of 4f 135p66p levels are calculated by summarizing electric dipole transition probabilities 4f 13 5p6 6p+ 4f 14 5p5 6p → 4f 13 5p65d, 4f 13 5p66s. Results: It’s been obtained that configuration essential mixing takes place for states with total angular momentum J = 3. Values of level lifetimes have been appeared to be insensitive to influence of configuration mixing. As to author’s opinion, it’s connected with that the lifetimes are defined by the probabilities of the most intensive transitions which in its turn, are the least sensitive to possible inaccuracies in calculation procedure. Practical significance: Values of lifetimes of levels 4f 13 5p6 6p in W VII spectrum, that are absent in contemporary databases at the moment, are practically significant.

Lifetime analysis of Te128,130 via the Doppler-shift attenuation method

Background: The $Z=52$ nuclei $^{128}\mathrm{Te}$ and $^{130}\mathrm{Te}$ are interesting candidates to study nuclear-structure properties close to the $Z=50$ shell. The knowledge of lifetimes of low-lying states in those nuclei is still scarce.Purpose: The goal of the present work is to extend the experimental database of nuclear level lifetimes of low-spin states in $^{128}\mathrm{Te}$ and $^{130}\mathrm{Te}$.Methods: Nuclear level lifetimes were determined by means of the Doppler-shift attenuation method (DSAM) using $p\ensuremath{-}\ensuremath{\gamma}$ coincidences measured at the SONIC@HORUS setup located at the FN-Tandem ion accelerator of the University of Cologne.Results: For $^{128}\mathrm{Te}$, lifetimes of eleven excited states could be determined, one of these for the first time. For the case of $^{130}\mathrm{Te}$, 18 nuclear level lifetimes were obtained, 15 for the first time. In both experiments, upper limits for lifetimes of several additional levels were determined. Moreover, the nuclear level scheme of $^{130}\mathrm{Te}$ could be extended. One additional level and 13 new transitions for levels above 2.7 MeV have been added. A standard shell-model calculation was performed and compared with the experimental results, showing an overall agreement.Conclusions: DSAM using $p\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences is a powerful tool to determine lifetimes in the subpicosecond range free of feeding contributions. Although both experiments yielded low statistics, numerous lifetimes could be obtained. The use of $p\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences furthermore enables the extension of level schemes.

High power downconversion deep-red emission from Ho3+-doped fiber lasers

Abstract It has been a big challenge in decades for Ho3+-doped fiber laser to produce high emission power in deep-red due to its intrinsic long carrier lifetime in 5I7 energy level. Here, we advance the development of this visible fiber lasers by a novel pumping method that leverages the advantages of blue laser diode downconversion mechanisms to fully pumping, while shortening the lifetime of the lower energy level of the deep-red laser through excited state absorption. For the first time, we demonstrate a downconversion fiber laser using a single wavelength of 532 nm solid-state laser pump source to excite the Ho3+-doped ZBLAN fiber, which achieves a record high maximum output power of 1.64 W at 752.10 nm, as well as free-running of deep-red lasers with watt-level output. This technology represents a milestone in high power deep-red fiber lasers. Importantly, it is readily to be extended to other wavelengths that evidenced its huge application potentials in fiber laser industry.

Fabrication and spectroscopic properties of hot-pressed Tb:CaF2 transparent ceramics with different doping concentrations

High quality of x at.% Tb:CaF2 (x = 1, 3, 5, 7, 9) transparent ceramics prepared by hot-pressed sintering achieved an average transmittance at 1500 nm of 88%. The effect of Tb3+ concentrations on the phase composition, microstructure, emission spectra, and fluorescence decay dynamics of Tb:CaF2 transparent ceramics were investigated. XRD and FESEM results demonstrated that the incorporation of Tb3+ did not cause significant changes in the crystal structure of CaF2, and the grain size gradually decreased with increasing Tb3+ doping concentration. Under the excitation of 350 nm, the strongest emission peak was located at 542 nm, which was attributed to the 5D4→7F5 transition of Tb3+. The green emission intensity enhanced linearly with increasing Tb3+ concentration from 1 at.% to 9 at.%. The fluorescence lifetime of 5D4 level was also investigated, and the values were comparable to the corresponding single crystals. All the results suggest that Tb:CaF2 transparent ceramic is a kind of potential green luminescence material.