Stark Splitting Research Articles

Spectral kinetic study of four-component BaF2–ZnF2–CdF2-YbF3 fluoride ceramics by selective laser excitation

New type of optical material, BaF2:ZnF2:CdF2:YbF3 (1.1 at %) ceramics, contains two phases with different chemical compositions and different crystal structures. BaF2:ZnF2:CdF2:YbF3 (1.1 at %) ceramics is translucent in visible and near-IR spectrum ranges, and it is transparent in mid-IR and terahertz ranges. The spectral-kinetic properties of Yb3+ optical centers in fluoride ceramics are studied by selective laser excitation. The qualitative spectral characteristics (homogeneous and inhomogeneous broadening, Stark splitting, and lifetimes) of Yb3+ optical centers are determined, and two phases with containing YbF3 as an impurity are revealed in this matrix. Two types of clustered Yb3+ optical centers with slow and short fluorescence decay are found, each in the different fluoride phase. The lifetimes of these Yb3+ centers in the first and second phases differ approximately by a factor of four (τ(77К) = 0.34/1.2 ms).

Growth, spectroscopy and first laser operation of monoclinic Ho3+:MgWO4 crystal

A monoclinic 0.86 at.% Ho3+:MgWO4 crystal is grown by the Top-Seeded-Solution Growth method. Its spectroscopic properties are studied with polarized light for E || a, b, c. The Ho3+ ion transition probabilities are determined within the modified Judd-Ofelt theory (mJ-O) accounting for the configuration interaction. The intensity parameters are Ω2 = 21.09, Ω4 = 4.42, Ω6 = 2.28 [10–20 cm2] and α = 0.053 [10-4 cm]. The calculated radiative lifetime of the 5I7 state is 6.18 ms. The Stark splitting of the 5I7 and 5I8 multiplets is determined with low-temperature spectroscopy. The absorption, stimulated-emission (SE) and gain cross-sections for the 5I8 ↔ 5I7 transition are derived. Ho3+:MgWO4 features a large Stark splitting of the ground-state (380 cm-1), high maximum σSE of 1.82 × 10–20 cm2 at 2.083 μm, broad gain spectra and high luminescence quantum yield making it suitable for efficient continuous-wave and mode-locked lasers at ∼2.1 μm. First laser operation of Ho3+:MgWO4 crystal is demonstrated at 2.104 μm reaching a slope efficiency of 72%.

NaYF4: Eu3+ microwires: Synthesis and the mechanism of stark splitting by monitoring time-resolved photoluminescence spectroscopy at high temperature

A new design of NaYF4: Eu3+ microwires (MWs) with a hexagonal structure were synthesized via a facile hydrothermal method assisted with the sodium citrate, and their microstructure and phase structure have been analyzed. The photoluminescence (PL) mechanism of β-NaYF4: Eu3+ MWs was systematically investigated under 532 nm laser excitation through adjusting MW number and excitation environment including the excited position, laser power, and temperature. The strongest emission peak originated from the 5D0→7F2 hypersensitive transition in this system. Furthermore, owing to the special temperature-dependent optical properties of β-NaYF4: Eu3+ MWs, time-resolved PL spectroscopy with high sensitivity is in situ real-time monitored at 1273 K to reveal the underlying mechanism of stark splitting. Therefore, our study should serve as a promising application in optical thermometry.

INFLUENCE OF PULSED ELECTRIC CURRENT ON THE WAVES MOTION CHARACTER OF PLASTIC DEFORMATION AT TENSION OF A STEEL PLATE

Infrared thermography and two-exposure speckle interferometry have been used to study the plastic deformation of low-carbon steel under the action of pulsed electric current. It was established that external electric effect leads to an increase in velocity of plastic waves by 65 %. Analysis of the velocity distribution patterns showed that they have the profile of “shock transition”. At the origin, velocity of the material is zero (motionless gripping), and at the right end of the curve material velocity is equal to stretching speed specified by testing machine. The effect of electric current leads to splitting of the displacements velocities, both at moving and stationary ends of the samples. It is assumed that the observed splitting is related to the Stark splitting of energy levels of the deformed system. This splitting leads to a decrease in the potential barrier for the motion of defects in crystal lattice. Thermographic studies have shown presence of a temperature gradient directed from clamps to center of the sample, which does not coincide with pattern of displacement distribution. It was determined that during the primary treatment with high power current pulses in the central area of the sample, sample temperature reaches 351 K, and 330 K in the area adjacent to clamps. Subsequent treatments result in a slight increase in temperature. This behavior of temperature can be explained by the fact that heat does not dissipate at a repetition rate of 10 Hz. On an average, sample temperature increases by 30 K. Theoretical calculation has shown that the Joule effect leads to an increase in temperature of the sample by 21 K per pulse, which is practically in agreement with experimental results. Estimates of thermal energy and energy of elastic deformation have shown that the fastest channel for converting the energy of electric pulse is structural changes in deformable system, which lead to the observed decrease in deforming force.

First results of upgraded beam emission spectrometer on EAST

The beam emission spectroscopy (BES) system that shares the collection optics with the core charge exchange recombination spectroscopy (cCXRS) has recently been upgraded on EAST. The enhanced system aims at the simultaneous measurements of the neutral beam emission from the co-current and counter-current neutral beam injection (NBI) as well as the active charge exchange line (Dα, n = 3→2, 656.1 nm) from the interaction of the main ions and the injected neutral beam. The operating spectral band of the system is 656.1 ± 6 nm, with respect to the maximum Doppler shift and stark splitting induced by the highest energy of 80 keV for deuterium beam. Strong edge Dα line is effectively suppressed by one curved chromate strip (˜3% transmission and ˜83 μm width) on the fused silica. Main ion Dα emission and beam emission spectra are acquired simultaneously without any saturation of the signal on the detector. In this paper, an overview of the upgraded spectrometer will be shown and the first experimental results are presented.

Features of the Angular Distribution of Light Scattered by a Cold Atomic Ensemble Placed in a Static Electric Field

The angular distribution of light scattered by a cold atomic ensemble placed in an external electric field is investigated analytically. It is shown that the Stark splitting of atomic levels substantially modifies the character of multiple scattering and, in particular, the effect of coherent backscattering of light. The possibility of using the described approaches in the diagnostics of magnetic nanofluids and perfect optical crystals is discussed.

A carnegieite type red emitting NaAlSiO4:Eu3+ phosphor: Concentration dependent time resolved photoluminescence and Judd-Ofelt analysis

This work discusses about synthesis of relatively unexplored carnegieite type NaAlSiO4 and designing it as efficient europium ion doped red phosphor. The synthesized powder has been systematically characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetry - Differential Thermal Analysis (TG-DTA) and photoluminescence (PL) techniques. The effects of Eu3+ concentration on the photoluminescence properties were investigated. Concentration dependent emission spectroscopic studies suggested quenching at 0.5% doping level due to multipolar interaction. Stark splitting analyses revealed that the point group around Na+ ions decreases with Eu3+ doping and it is found to be C4v in Eu3+ doped NaAlSiO4. The asymmetry ratio was found to increase monotonically with europium concentration due to increasing density of sodium ion vacancies (VNa) which further distort the structure of NaAlSiO4. Lifetime spectroscopic studies suggested stabilization of europium ion at sodium site in two different environment; one nearer to charge compensating defect and one at far off distance. Judd-Ofelt analysis suggested asymmetric and highly polarizable environment around europium ion lead to enhanced red emission. The structure-property correlations indicate the potential of such structures for enhanced luminescence, scintillation and other optoelectronic properties.

Boosting the branching ratio at 900 nm in Nd3+doped germanophosphate glasses by crystal field strength and structural engineering for efficient blue fiber lasers

Fine tuning of Stark splitting and the dispersed state of Nd3+to boost the fluorescence branching ratio and emission intensity of the4F3/2→4I9/2transition.

Optical resonance near the edge of a photonic band gap (PBG): turning the effects of a PBG on/off using a resonant driving field

ABSTRACTWe studied the effects of a coherent monochromatic resonant laser field driving the transition of a two-level atom embedded in a photonic band gap (PBG) material on the emission dynamics of the atom. When the transition frequency of the atom lies outside a PBG and sufficiently far from the band edge that the emission dynamics of the atom is not normally affected by the gap, the dynamic stark splitting of the upper level of the atom into two dressed states by a sufficiently strong resonant driving field can bring the lower dressed state close enough to the band edge or even inside the gap so as to be affected by the gap, providing a switchable means of extending the novel effects of atom–photon interaction near the edge of a PBG for atomic transitions outside the gap and far from the band edge. The net effect is as if a sufficiently strong resonant field driving a transition of an atom embedded in a PBG actively shifts the PBG close enough to the transition so that the gap affects the emission dynamics associated with the transition.

NV−–N+ pair centre in 1b diamond

With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV−–N+ pairs. There can be a small percentage of neutral charge NV0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV− zero-phonon has been altered. The alteration arises from a change of the distribution of N+ ions and a modification of the average electric field at the NV− sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV− centres enhances the density of close N+ ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N0 in the lattice results in more distant distribution of N+ ions and a narrowing of the ZPL. The competition between NV− and N0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV− and N0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV−–N+ pairs in diamond. There is a critical dependence on pair separation. When the NV−–N+ pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV– to N+ and an optical cycle that involves NV0. The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV− in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV− are required. As well as extensive measurements of the NV− optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported.

11 W continuous-wave laser operation at 209 μm in Tm:Lu16Sc04O3mixed sesquioxide ceramics pumped by a 796 nm laser diode

High quality thulium doped Lu1.6Sc0.4O3 mixed sesquioxide laser ceramics were fabricated using a solid-state reactive sintering method. Optical and spectroscopic properties of the ceramics were studied. A high transmittance almost identical to the theoretical value of the ceramics was reached at the lasing wavelength. A large Stark splitting of 920 cm−1 for the ground states 3H6 and 472 cm−1 for the first excited states 3F4 of Tm3+ were observed, resulting in a long wavelength emission band around 2.09 μm with low reabsorption losses at this wavelength. CW laser operation at 2.09 μm pumped by a 796 nm laser diode was achieved with an output power of 11 W and an optical-to-optical conversion efficiency of 28.9%, both of which are the highest values reported so far for lasing around 2.1 μm in Tm3+ doped mixed sesquioxide ceramics.

Method for estimating the Stark splitting of rare-earth ions from the measured cross-section spectra.

A method to estimate the Stark levels of the rare-earth ions doped in a laser medium from the measured emission and absorption cross-sections is proposed. The method is based on the McCumber theory, which can calculate the emission/absorption cross-sections from the given Stark levels. By fitting the calculated emission/absorption spectra to the measured ones through a numerical optimization process, the Stark levels of the RE ions can be determined. As examples, the Stark levels of the laser-emission-related manifolds of Er3+ and Yb3+ ions in a gain fiber and two doped glasses have been determined by the proposed method. The data were then used to analyze the temperature-dependent population of the Stark levels. This method avoids the difficulties in direct measurement of the Stark levels in a cryogenic temperature environment. It is important to the evaluation of the thermal load, distribution, and design of the thermal management system of high-power fiber lasers and amplifiers.

Specific Features of Interatomic Dipole–Dipole Interaction near a Perfectly Conducting Charged Surface

Specific features of dipole–dipole interaction between two motionless point atoms located near a perfectly conducting charged plate are investigated theoretically within a consistent quantum microscopic approach. These features are analyzed on the basis of the dynamics of cooperative spontaneous decay of excited states of a diatomic quasimolecule. The decay rate is investigated as a function of the interatomic distance, the orientation angle of the quasimolecule with respect to the plane of the plate, and the distance between the quasimolecule and the plate. It is shown that the conducting plate significantly modifies the character of dipole–dipole interaction even when the plate is not charged. When the plate is charged, the Stark splitting of atomic levels leads to an additional modification of the interatomic interaction. The features observed are explained on the basis of the analysis of the spectrum of collective states of diatomic molecules.

Using motional Stark splitting of emission to constrain MHD equilibrium analysis in DIII-D plasmas.

We report tests of an alternate technique for constraining MHD equilibrium analysis in tokamak plasmas using internal magnetic field measurements based on | B | measurements from the motional Stark splitting of Dα spectral lines emitted by a neutral heating beam (MSE-LS). We compare results using MSE-LS with those of the standard equilibrium analysis technique based on line polarization of the Dα emission (MSE-LP). An alternative to MSE-LP is needed in future devices such as ITER where MSE-LP will be difficult due to a plasma-induced coating of the first optical element. The tests utilized data from 10 DIII-D shots with 7 MSE-LS and 14 MSE-LP views covering a range of radii along the outer midplane of the plasma. Seven MSE-LS measurements can contribute significantly to the equilibrium reconstruction of pressure and q profiles using both synthetic and experimental DIII-D MSE-LS data. For example, 7 MSE-LS plus seven MSE-LP measurements give a fit quality that is as good as the same cases with 14 MSE-LP measurements. Analyzing synthetic data for 14 MSE-LS measurements shows significant improvement in fitting quality over the case with 7 MSE-LS locations.

Ultraviolet optical excitation of near infrared emission of Yb-doped crystalline aluminum oxynitride thin films

Yb3+ ions hold promises for high power emission in the near infrared (NIR). Yet, relevant matrices, comprising mediators to excite Yb3+, have to be found and the optical mechanisms have to be studied in detail. The purpose of this study is to report on the optical excitation and emission mechanisms of NIR photoluminescence (PL) of Yb-doped crystalline aluminum oxynitride thin films prepared at room temperature using reactive magnetron sputtering. Crystal structure and chemical composition are analyzed by transmission electron microscope and Rutherford backscattering spectrometry, respectively. Photoluminescence spectroscopies are used to investigate the excitation and emission mechanisms. NIR emission at 985 nm is obtained under indirect optical excitation using the 325 nm line of a He-Cd laser, the excitation mechanism is explored by photoluminescence excitation measurement (PLE), and the fine structure of the emitted energy levels is investigated by performing PL measurements at low temperature (LTPL). PLE shows that the host defects play the role of mediators to transfer the excitation energy to Yb ions. This offers different possibilities for the development of multiple excitation channels for Yb3+. Stark splitting of the energy levels of the 2F5/2 and 2F7/2 transitions is evidenced using LTPL in the 78 to 295 K range. Electronic transitions are ascribed to experimental emission lines based on good agreement with theoretical values. Moreover, the activation energies for PL thermal quenching are determined and correspond to the energy difference between highest energy quenched lines and thermally activated “hotlines.”

Influence of the cathode material in the cathode fall characteristics of a hydrogen hollow cathode glow-discharge

In this work, we present Doppler free two photon optogalvanic measurements to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of hydrogen. The main aim of this article is the comparison of the measurements made with different cathode materials, stainless steel, and tungsten; both of them are widely used in the low-pressure discharges. Sputtering of stainless steel is the principle cause of the differences observed for the E-field variation, and the differences are analyzed in the frame of the sputtered material in a wide range of discharge conditions. Complementary images of the discharge luminosity allow for the conclusion; the cathode dark zone corresponds in good approximation to the cathode fall length.

A step towards synthesizing unique UV and visible light excitable AWO4:Eu3+ (A = Ca and Sr) nanophosphors using high energy ball milling method: luminescence differences in going from Ca2+ → Sr2+

Multicolour excitable scheelite type CaWO4:Eu3+ (CEW) and SrWO4:Eu3+ (SEW) nanophosphors were synthesized using high energy ball milling in nano-domain. The synthesized nanophosphors were characterized extensively using Rietveld analysis of X-ray diffraction data, Raman spectroscopy, electron microscopy, energy dispersive spectroscopy and selected area electron diffraction. Differences in optical characteristics of CEW and SEW are probed using time resolved photoluminescence spectroscopy. It was observed that aliovalent doping of Eu3+ in CaWO4 and SrWO4 at divalent Ca/Sr sites leads to formation of cation vacancies as confirmed using positron annihilation lifetime spectroscopy (PALS). PALS also revealed that defect density in SEW is more than CEW which degrades its optical performance by aiding in non-radiative relaxation. The close proximity in ionic radius of Eu3+ and Ca2+ ions leads to better structural homogeneity in case of CEW and less lattice distortion which is reflected in its high emission output and quantum yield. Stark splitting analyses revealed reduction in symmetry around europium ion in SEW as compared to CEW. This is reflected in high asymmetry ratio (EDT/MDT) in case of SEW which directly translates into its high luminescence lifetime. Lifetime spectroscopy also revealed that in both the samples europium ion is localized at two different environments; one closer to defect centre and one is far off. Our study indicates that both these nanophosphors have unique ability to get excited intensely by UV as well as visible light and emit very intense red light which can be explored in phosphor converted white LEDs. Judd–Ofelt analysis indicates better optical performance of CEW as compared to SEW phosphor.

Luminescence properties of Eu3+-activated TbAlO3 perovskite compound synthesized by metal organic decomposition

Eu3+-activated TbAlO3 perovskite (TAP:Eu3+) phosphor was synthesized by metal organic decomposition and subsequent calcination at Tc = 1200 °C in air. The luminescence properties of the TAP:Eu3+ phosphor were investigated in detail by photoluminescence (PL) spectroscopy and PL excitation (PLE) spectroscopy, together with PL decay measurements. The PLE spectra and PL decay behaviors of the Eu3+ and Tb3+ emissions showed evidence of resonant energy transfer from the TAG host (Tb3+) to Eu3+. The temperature dependence of the Eu3+ emission intensity was measured at T = 10–450 K and analyzed using the conventional quenching model with the addition of the phonon occupation number term, which was promising for gaining the parity-forbidden Eu3+ transition intensity. This study was also focused on a lattice site of the Eu3+ dopant ions substituting whether for the A-site (Tb3+) or B-site (Al3+) in the TAP lattice. The Stark splitting of the 5D0 to 7FJ level transitions suggests that the Eu3+ ions are substituted for the A-site with the point symmetry Cs.

Microwave-assisted synthesis and characterization of Y2O3 : Eu(III)-benzoate hybrid nanophosphors

The optical and structural characteristics of Y2O3 : Eu (III)-benzoate hybrid nanophosphors, synthesized by the microwave-assisted solvothermal technique, are reported in this work. Benzyl alcohol was used during the synthesis, carried out at low temperatures in the microwave reactor, to obtain the Y2O3 : Eu(III)-benzoate-layered hybrid nanophosphors. The benzyl alcohol led to the incorporation of benzene rings (belonging to benzoate group) around the Y2O3 : Eu(III) molecules, promoting a lamellar structure and showing the previously reported luminescent “antenna effect” in the nanophosphors. Y2O3 : Eu(III)-benzoate nanophosphors showed a high photoluminescence emission intensity at 590, 612, 650, and 697 nm due to the interelectronic D05 to F17, F27, F37, and F74 transitions of the europium ions. A stark split might be present due to the variation of the annealing temperature given to the Y2O3 : Eu(III)-benzoate nanophosphors. The nanostructured hybrids showed the appearance of complex morphologies similar to flower petals. The as-obtained nanophosphors were in the range of ∼20 nm and showed the reported x-ray diffraction reflections for these kinds of materials.

Influence of F– on stark splitting of Yb3+ and the thermal expansion of silica glass

A local phosphate/fluoride environment of Yb3+ was created in silica glass using a multi-step method. The influence of F- on the Stark splitting of Yb3+ in Al3+/P5+/F- co-doped silica glass was studied at room-temperature, in addition to its effect on the thermal expansion performance of the glass matrix. The results indicate that Yb3+ ions in Al3+/P5+/F- co-doped silica glass have a larger Stark splitting energy of 2F7/2 compared to Al3+/P5+ co-doped silica glass. Moreover, a larger integrated absorption cross-section (34.58 pm2 × nm), stimulated emission cross-section (0.63 pm2), and better thermal expansion performance (1.3062 × 10−6 K- at 100 °C) are achieved in Al3+/P5+/F- co-doped silica glass. Finally, different function mechanisms of F- in silica and phosphate glasses were analyzed and the F-Si bond was used to explain the results in silica glass. The combination of low refractive index, large Stark splitting energy of 2F7/2, and small thermal expansion makes Al3+/P5+/F- co-doped silica glass a preferred material for large mode area fibers for high-power laser applications.