Energy Level Scheme Research Articles

Energy levels and emission parameters of theDy3+ ion dopedinto the YPO4 host lattice

Single crystals of Dy3+-doped YPO4 havebeen grown from Pb2P2O7 flux and investigated by optical spectroscopy techniques. The energy level scheme of theactive ion has been deduced from the low temperature spectra and reproduced by means ofa crystal-field calculation. The room temperature absorption spectra have been analysed inthe framework of the Judd–Ofelt approach, and the results of this analysis havebeen applied in a discussion concerning the spectral composition of the visibleluminescence.

Near-IR absorption saturation and mechanism of picosecond recovery dynamics of copper selenide nanostructured via alumina

Absorption saturation at 1.064 μm wavelength in Cu2−xSe material nanostructured by means of an original method—formation and hosting in an array of electrochemically grown alumina voids—was investigated. Columnlike channels provide growth of copper selenide in a shape of nanowire with a fixed diameter. Experimental results obtained from measuring nanowires of various diameters (∅10, 15, 20, and 70 nm) revealed that the ∅20 nm case is most efficient for absorption saturation, manifesting highest optical modulation depth and lowest interlevel transition rate evaluated. A model to analyze the conditions for absorption saturation and absorption recovery dynamics was developed. Depending on pump intensity the nonmonotonous increase in recovery time for the highest applied values was interpreted as filling up of states at an intermediate energy level. From modeling, important material science parameters, such as concentration of resonant and trapping/recombination states, interlevel transition rate, capture time, characteristic for copper selenide, have been evaluated and compared for different samples. Finally, the consequence of the model to a working copper selenide energy level scheme was considered.

Assignment of4f−5dabsorption bands in Ce-dopedRAlO3(R=La, Gd, Y, Lu) perovskites

An intuitive assignment of absorption bands of Ce-doped $R{\text{AlO}}_{3}$ ($R=\text{Gd}$, Y, and Lu) perovskites suggested by some authors is compromised. We use semiempirical approaches based on the extended H\uckel method to calculate the energy-level scheme of the cluster containing Ce and its nearest O neighbors in true $R{\text{AlO}}_{3}$ ($R=\text{La}$, Gd, Y, and Lu) structures. Our calculations show a different origin for the energy levels involved in the absorption process than might intuitively be suggested. Some quantitative aspects also reasonably correspond to experimental observation.

Electromagnetically induced transparency in acetylene molecules with counterpropagating beams in V and Λ schemes

We report on the experimental observation of electromagnetically induced transparency in V and Λ energy level schemes using counterpropagating coupling and probe beam geometry. The observation was achieved using an acetylene photonic microcell. The conditions required for this observation are explored theoretically, and we show that the use of counterpropagating beams in electromagnetically induced transparency may have applications as a spectroscopic technique where velocity discrimination is desirable.

NIR to visible up-conversion, infrared luminescence, thermoluminescence and defect centres in Y2O3 : Er phosphor

Er3+ doped Y2O3 phosphor was prepared by the solution combustion method and characterized using powder x-ray diffraction and energy-dispersive analysis of x-ray mapping studies. Room temperature near infrared (NIR) to green up-conversion (UC) emissions in the region 520–580 nm {(2H11/2, 4S3/2) →4I15/2} and red UC emissions in the region 650–700 nm (4F9/2 →4I15/2) of Er3+ ions have been observed upon direct excitation to the 4I11/2 level using ∼972 nm laser radiation of nanosecond pulses. The possible mechanisms for the UC processes have been discussed on the basis of the energy level scheme, the pump power dependence as well as based on the temporal evolution. The excited state absorption is observed to be the dominant mechanism for the UC process. Y2O3 : Er exhibits one thermally stimulated luminescence (TSL) peak around 367 °C. Electron spin resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the centres responsible for the TSL peak. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centres. One of them (centre I) with principal g-values g|| = 2.0415 and g⊥ = 2.0056 is identified as centre while centre II with an isotropic g-factor 2.0096 is assigned to an F+-centre (singly ionized oxygen vacancy). Centre III is also assigned to an F+-centre with a small g-factor anisotropy (g|| = 1.974 and g⊥ = 1.967). Additional defect centres are observed during thermal annealing experiments and one of them appearing around 330 °C grows with the annealing temperature. This centre (assigned to an F+-centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and the F-centre appears to correlate with the observed TSL peak in Y2O3 : Er phosphor. The trap depth for this peak has been determined to be 0.97 eV from TSL data.

Luminescence properties of Dy 3+:GdAlO 3 nanopowder phosphors

Different concentrations of dysprosium (Dy 3+) doped gadolinium aluminates (GdAlO 3) have been newly synthesized by the wet chemical route method. Very fine particles in the nanometer range could be prepared by this method, as evidenced by X-ray diffraction and SEM measurements. The XRD profile confirms their orthorhombic nature, which is well correlated with the reported results. Luminescence studies on these compounds have been carried out on the emission and excitation, along with lifetime measurements. Such luminescent powders are expected to find potential applications as new optical materials. The emission procedure in the system has also been elucidated by an energy level scheme.

Ultrasonic study of the Yb-based heavy fermion compound YbRh2Zn20

We report ultrasonic measurements on the high quality single crystal of the Yb-based heavy fermion compound YbRh2Zn20 over a temperature range from 200 K to 0.5 K. A shallow, but clear minimum was observed in the temperature dependent elastic constants C11, (C11 – C12)/2 and C44 around 15 K, probably attributed to the ground state and low-lying excited states of Yb3 in the cubic CEF. We discuss the low-temperature elastic properties and possible energy level scheme of localized 4f state of Yb3 ions in YbRh2Zn20.CEF ground state developed at the low temperatures and physical parameters relating to a quadrupolar moment in YbRh2Zn20

The photoluminescent quenching behaviors of Na3La9O3(BO3)8:Tb3+ phosphors

The quenching behaviours of 5D4-7F6 emission of Tb3+ in Na3La9O3(BO3)8:Tb3+ under 125-300nm excitation were systematically investigated. The results revealed that its luminescent quenching concentrations excited at particular wavelengths were dependent on corresponding excitation bands. On analyzing the luminescent quenching characteristics, all these spin-orbit 4f-5d transitions of Tb3+ and host absorption band in Na3La9O3(BO3)8:Tb3+ were identified in excitation spectrum and the energy levels scheme of Tb3+ in Na3La9O3(BO3)8:Tb3+ system was first established.

Description of Nuclear Structures with Brueckner-AMD plus J Projection

We propose a new approach that makes the antisymmetrized molecular dynamics (AMD) available to us with realistic nuclear interactions. In this method, the Bethe-Goldstone equation in the Brueckner theory is solved for every nucleon pair described by wave packets of AMD, and the G-matrix is calculated with single-particle orbits in AMD self-consistently. Furthermore, the spin and parity projection is performed correctly using the two-body correlation functions derived from the solutions of the Bethe-Goldstone equation. In this work, we apply this framework to not only α-nuclei but also N �= Z nuclei with A ∼ 10. It is confirmed that these results present the description of reasonable cluster structures and energy-level schemes comparable with the experimental ones in light nuclei. Subject Index: 206, 210

Optical spectroscopy in CoO: Phononic, electric, and magnetic excitation spectrum within the charge-transfer gap

The reflectivity of single-crystalline CoO has been studied by optical spectroscopy for wave numbers ranging from 100 to $28\text{ }000\text{ }{\text{cm}}^{\ensuremath{-}1}$ and for temperatures $8lTl325\text{ }\text{K}$. A splitting of the cubic IR-active phonon mode on passing the antiferromagnetic phase transition at ${T}_{N}=289\text{ }\text{K}$ has been observed. At low temperatures the splitting amounts to $15.0\text{ }{\text{cm}}^{\ensuremath{-}1}$. In addition, we studied the splitting of the cubic crystal-field ground state of the ${\text{Co}}^{2+}$ ions due to spin-orbit coupling, a tetragonal crystal field, and exchange interaction. Below ${T}_{N}$, magnetic-dipole transitions between the exchange-split levels are identified, and the energy-level scheme can be well described with a spin-orbit coupling $\ensuremath{\lambda}=151.1\text{ }{\text{cm}}^{\ensuremath{-}1}$, an exchange constant $J=17.5\text{ }{\text{cm}}^{\ensuremath{-}1}$, and a tetragonal crystal-field parameter $D=\ensuremath{-}47.8\text{ }{\text{cm}}^{\ensuremath{-}1}$. Already in the paramagnetic state electric-quadrupole transitions between the spin-orbit split level have been observed. At high frequencies, two electronic levels of the crystal-field-split $d$ manifold were identified at $8\text{ }000$ and $18\text{ }500\text{ }{\text{cm}}^{\ensuremath{-}1}$.

Tb3+inTbCo3B2: A singlet ground state system studied by inelastic neutron scattering

The results of inelastic neutron scattering on the hexagonal compounds ${\text{TbCo}}_{3}{\text{B}}_{2}$ and ${\text{Tb}}_{0.75}{\text{Y}}_{0.25}{\text{Co}}_{3}{\text{B}}_{2}$, at several temperatures, are reported. The crystal-field level scheme of ${\text{Tb}}^{3+}$ ions in the paramagnetic phase is determined. This scheme contains a nonmagnetic singlet $({\ensuremath{\Gamma}}_{1})$ as the ground state. Inelastic neutron scattering at low temperature (10 K) leads to a different energy-level scheme, where the singlet ground state is ferromagnetic with $⟨{J}_{x}⟩\ensuremath{\ne}0$. This is a ``self-induced'' ferromagnetism on the Tb sublattice, resulting from the admixture of higher crystal-field levels into the singlet ground state by the exchange field. The resulting magnitudes of these ground state magnetic moments are $5.6(3){\ensuremath{\mu}}_{B}$ and $3(1){\ensuremath{\mu}}_{B}$ for ${\text{TbCo}}_{3}{\text{B}}_{2}$ and ${\text{Tb}}_{0.75}{\text{Y}}_{0.25}{\text{Co}}_{3}{\text{B}}_{2}$, respectively. These values are much smaller than the free ion value of $9{\ensuremath{\mu}}_{B}$ and are in agreement with previously observed values. Such large reductions are characteristic of the ``self-induced'' ferromagnetism. The temperature dependences of the magnetic moment, magnetic anisotropy, Tb sublattice dilution, and magnetic susceptibility are discussed.

Luminescence properties of sol–gel-derived TiO 2:Sm powder

Sm-doped TiO 2 nanopowder phosphors were prepared by employing a sol–gel route. Thermal treatment crystallizes the powder in anatase phase and leads to a quite efficient (quantum yield ∼15%) Sm 3+ luminescence with a well-resolved fine structure under optical excitation within the fundamental absorption band of the host. From the PL spectrum and its temperature dependence the energy level scheme of Sm 3+ in crystalline powder of anatase was obtained and analyzed based on symmetry considerations. In the case of host-mediated excitation we found a relatively long-lasting afterglow of Sm 3+ emission characterized by a nearly power-law kinetics. The overall intensity of Sm 3+ emission increased with temperature. The origin of the behavior, connected to the migration and relaxation of host electronic excitations, are discussed.

Matched slow pulses using double electromagnetically induced transparency

We implement double electromagnetically induced transparency (DEIT) in rubidium vapor using a tripod-shaped energy-level scheme consisting of hyperfine magnetic sublevels of the 5S1/2-->5P1/2 transition. We show experimentally that through the use of DEIT one can control the contrast of transparency windows as well as group velocities of the two signal fields. In particular, the group velocities can be equalized, which holds promise to greatly enhance nonlinear optical interaction between these fields.

Hyperfine interactions in szomolnokite (FeSO 4·H 2O)

The temperature dependencies of the ferrous Mössbauer parameters for synthetic szomolnokite are determined in the range between 4 and 450 K. A magnetic order-disorder transition is observed at 29.6 ± 0.5 K. The Mössbauer spectra in the paramagnetic region are well fitted by the superposition of a Fe 2+ distributed quadrupole component and a small ferric doublet component. The spectra in the magnetic region are typically for Fe 2+, showing up to eight absorption lines. They are analyzed from diagonalization of the full nuclear-interaction hamiltonian. The saturation value of the hyperfine field is 32.5 T. For temperatures below 29 K, the adjusted value for the asymmetry parameter of the EFG is η ≈ 0.63 and for the quadrupole splitting Δ E Q ≈ 3.08 mm/s. These values are in line with those measured at temperatures in the paramagnetic regime. The temperature dependence of the quadrupole splitting is interpreted within the ferrous 5D orbital energy level scheme by a crystal field calculation based on the point symmetry of the Fe 2+ site in szomolnokite. It is found that the high asymmetry of the EFG is caused by the presence of the H 2O groups in the structure. The variation of the hyperfine field with temperature is interpreted within the molecular field approximation, however, taking exchange magnetostriction into account. From the temperature dependence of the isomer shift the characteristic Mössbauer temperature Θ M is determined to be 425 K, from which the Mössbauer fraction at room temperature is estimated to be 0.79.

Photoconductivity and thermally stimulated current in CaGa2S4single crystals doped with Eu2+and Ce3+

Photoconductivity (PC) measurements are carried out on single crystals of CaGa2S4 doped with Ce3+ and Eu2+ at room temperature and at about 30 K. Low temperature PC spectra can only be measured for Ce doped samples but not for Eu ones owing to too high resistivity. Based on the data obtained, the energy level scheme of Ce3+ ions is discussed in reference to the optical band edge. Single crystals of CaGa2S4 are grown by codoping Ce3+ with Na+ ions to observe the charge compensation effect expected to occur under the substitution of Ca2+ ions by Ce3+ ions. Their electrical resistivity is reduced about two orders in magnitude from ca. 1013 Ω cm to ca. 1011 Ω cm without much change in PC spectra, suggesting a mere decrease in scattering centers for carriers. From the variation in DC resistivity with time, it is expected that many carrier traps may exist in the compounds. To clarify those trap levels the thermally stimulated current (TSC) is measured using samples with different Ce3+ concentrations. From the analysis of TSC spectra, 6 traps with different depths have been retrieved. We have also found traps which may have repelling potential barriers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of solid-state saturable absorbers with temperature dependent absorption cross-sections

We describe a comprehensive model which can be used in the continuous-wave (cw) analysis of solid-state transition metal-doped saturable absorbers, which, in addition to the commonly observed temperature dependence of the refractive index and fluorescence lifetime, also exhibit a temperature dependent absorption cross-section. By using a rate equation analysis, two coupled differential equations are derived for the beam power and the q-parameter of the pump beam. To test the validity of the model, we analyzed the cw and pulsed saturation data taken with Cr 4+:forsterite crystals which are subject to these three thermal effects at 1064 nm. Data for electric field parallel to the crystal b-axis ( E ‖ b ) and c-axis ( E ‖ c ) were analyzed. Results indicate that when thermal loading effects are taken into account, better agreement is obtained between the cross-section results of the cw and pulsed saturation data. In particular, inclusion of thermal effects reduced the fractional deviation between the average cw and pulsed cross-section values from 23% to 2% and from 34% to 29% for the E ‖ c and E ‖ b cases, respectively. In the E ‖ b case, the average absorption cross-section and the normalized strength of excited-state absorption were further determined to be 5.98 × 10 −19 cm 2 and 0.45, respectively. The presented model can be readily extended to analyze other thermal effects or other media with different energy-level schemes.

Luminescence of Pb2+ ions in YAG:Pb single‐crystalline films

AbstractLuminescence of Pb2+ ions in YAG:Pb single‐crystalline films (SCF) with different lead content in the range of 0.01–0.3 at% was investigated by means of cathodoluminescence, time‐resolved emission/excitation spectra and luminescence decay kinetic under excitation by synchrotron radiation. The nature of Pb2+ ion‐related emission bands in the UV and visible ranges and their prevailing excitation mechanism are considered. Strong mixing of the 1P1 excited states of Pb2+ ions and the conduction‐band states of the YAG host was found. A scheme of energy levels of Pb2+ center in YAG and LuAG is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3(BO3)8:Tb3+ Phosphor

The novel vacuum ultraviolet (VUV) excited Na3Y9O3(BO3)8:Tb3+ (NYOB:Tb3+) green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb3+ (20 wt%) are observed in NYOB:Tb3+ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4f-5d transitions of Tb3+ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb3+ in NYOB:Tb3+ is first established. This newly developed NYOB:Tb3+ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4:Mn2+ and would be a potential VUV-excited green phosphor.

Site‐selective spectroscopy of erbium in wide band gap semiconductors

AbstractIn this paper results of site‐selective spectroscopy of Er3+ ions in wide band gap semiconductors, such as cubic and hexagonal GaN, and 6H SiC are presented. Photoluminescence excitation (PLE) spectroscopy was applied to find the Stark splitting pattern of energy levels in the 4I9/2 manifolds. It is shown that in cubic and hexagonal GaN only one center dominates. In the case of wurtzite GaN it is most probably due to Er occupying a Ga site, whereas in the cubic phase point‐charge model calculations suggest a slightly distorted, Td interstitial site. In 6H SiC three different centers were distinguished. The energy level schemes for the 4I9/2 and the ground 4I15/2 states were determined for all three centers, basing on the results of photoluminescence and PLE measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic characteristics of Tm 3+ in Tm and Tm, Nd, Yb:Sc 2O 3 ceramic

The spectroscopic investigation of Tm 3+ or (Nd, Yb, Tm)-doped Sc 2O 3 transparent ceramics, as laser-active media for visible and IR emission, was performed. The spectra are dominated by Tm 3+ ions in sites of C 2 symmetry and an energy level scheme and other spectral parameters were determined. The strong concentration quenching of 3H 4 level emission in Tm:Sc 2O 3 at 300 K is discussed by considering the resonant cross-relaxation ( 3H 4→ 3F 4)−( 3H 6→ 3F 4) process and multipolar interactions of various orders. The main energy-transfer processes leading to the blue upconversion emission from the 1G 4 Tm 3+ level in (Tm, Nd, Yb):Sc 2O 3 ceramic, under pulsed pumping at 808.3 nm were evidenced.