Optical Emission Cross Sections Research Articles

TDDFT versus GW/BSE Methods for Prediction of Light Absorption and Emission in a TADF Emitter.

Design concepts for organic light emitting diode (OLED) emitters, which exhibit thermally activated delayed fluorescence (TADF) and thereby achieve quantum yields exceeding 25%, depend on singlet-triplet splitting energies of order kT to allow reverse intersystem crossing at ambient temperatures. Simulation methods for these systems must be able to treat relatively large organic molecules, as well as predict their excited state energies, transition energies, singlet-triplet splittings, and absorption and emission cross sections with reasonable accuracy, in order to prove useful in the design process. Here we compare predictions of TDDFT with M06-2X and ωB97X-D exchange-correlation functionals and a GoWo@HF/BSE method for these quantities in the well-studied DPTZ-DBTO2 TADF emitter molecule. Geometry optimization is performed for ground state (GS) and lowest donor-acceptor charge transfer (CT) state for each functional. Optical absorption and emission cross sections and energies are calculated at these geometries. Relaxation energies are on the order of 0.5 eV, and the importance of obtaining excited state equilibrium geometries in predicting delayed fluorescence is demonstrated. There are clear trends in predictions of GoWo@HF/BSE, and TDDFT/ωB97X-D and M06-2X methods in which the former method favors local exciton (LE) states while the latter favors DA CT states and ωB97X-D makes intermediate predictions. GoWo@HF/BSE suffers from triplet instability for LE states but not CT states relevant for TADF. Shifts in HOMO and LUMO levels on adding a conductor-like polarizable continuum model dielectric background are used to estimate changes in excitation energies on going from the gas phase to a solvated molecule.

Triple-Wavelength Lasing with a Stabilized β-LaBSiO5:Nd3+ Crystal.

Multi-wavelength lasers, especially the triple-wavelength laser around 1060 nm, could be produced by the 4F3/2 → 4I11/2 transition of Nd3+ and present numerous challenges and opportunities in the field of optoelectronics. The Nd3+-doped high-temperature phase of LaBSiO5 (β-LBSO) is an ideal crystal to produce triple-wavelength lasers; however, the crystal growth is challenging because of the phase transition from β-LBSO to low-temperature phase (α-LBSO) at 162 °C. This phase transition is successfully suppressed when the doping content of Nd3+ is larger than 6.3 at. %, and the Nd3+-doped β-LBSO is stable at room temperature. The local disorder of BO4 tetrahedra due to Nd3+ doping is essential to the stabilization of β-LBSO. For the first time, the β-LBSO:8%Nd3+ crystal with a dimension of 1.8 × 1.8 × 1.8 cm3 is obtained through the top-seeded solution method. The crystal shows strong optical absorption in the range of 785-815 nm, matching well with the commercial laser diode pumping source. The optical emission of 4F3/2 → 4I11/2 splits into four peaks with the highest optical emission cross section of 2.14 × 10-20 cm2 at 1068 nm. The continuous-wave triple-wavelength generation of coherent light at 1047, 1071, and 1092 nm is achieved with the highest output power of 235 mW and efficiency of 12.1%.

Structure, and opto-dielectric investigations of Cu2+ -doped calcium bismuth silicate glass ceramics

CuO inclusive silicate glasses are well known for various semiconductor applications. However, there is a lot of demand and necessity of high efficient opto-dielectric materials. In view of this, the glasses of chemical composition (30 – x) CaO + (10) Bi2O3 + (60) SiO2 + (x) CuO have been synthesized and studied for their structural, optical and dielectric characterization techniques. Glassy behaviour of CuO undoped glass and ceramic behaviour of all other CuO doped glasses conformed by structural characterization. The elastic modulus and micro hardness of glass and glass ceramics reveal their inter connected covalent structure. Trap depth parameters (Tm, Eτ, Eδ, Eω & μs) have been determined and analysed under irradiation, and found that 0.3 mol% CuO -doped glass ceramic under 30 kGy of irradiation dose exhibiting better TL output. Dielectric relaxation studies of the glass ceramics suggested that mixed conduction of both ionic and electronic. Observed dielectric results; dielectric constant (εr), dielectric loss (tanφ), temperature region of relaxation (ΔT), low activation energie's for conduction (Ea) and AC Conductivity (σac) suggesting that the glass ceramics are dielectric. Optical band gap (Eo), transition probability (At) and emission cross section (σ) corresponding to the emissive transition 3D1 → 1S0 assessed by optical techniques. All the results suggests that 0.3 mol% CuO -doped glass ceramic is a useful opto-dielectric resource.

Role of Mn2+ ions on optical and luminescent properties of CaF2–Y2O3–ZnO–B2O3–SiO2 glasses

MnO doped CaF2–Y2O3–ZnO–B2O3–SiO2 glasses were synthesized. Different physical parameters of these glass materials such as density, molar volume, electronegativity, optical basicity and refractive index were calculated. The glass transition and glass crystallization temperatures of these glasses were measured by DTA analysis. The mechanical properties such as Young’s modulus, Shear modulus, Bulk modulus, Poisson’s ratio and microhardness of these materials were also calculated. Different characterization such as FT-IR, ESR, DC conductivity, optical absorption and photoluminescence were carried out on the prepared glass samples. ESR studies of these glass materials exhibited sextet at lower concentrations of MnO. The optical bandgap, Urbach energy, transition probability and emission cross section of these glass materials were calculated. Semiconducting nature of these glass materials was also observed due to the significant increase in BO3 and MnO6 units with increasing concentration of MnO. Optical absorption studies revealed that the increase in intensity of different octahedral peaks were due to the increase in concentration of MnO. Photoemission occurs around 545 to 567.3 nm suggested that the emission was red-shifted for higher MnO concentration and green-shifted for lower MnO concentration.

Role of Mn2+ ions on optical and luminescent properties of LiF–Sb2O3–ZnO–B2O3–SiO2 glasses

MnO doped LiF–Sb2O3–ZnO–B2O3–SiO2 glasses were synthesized by melt quenching technique. Different physical parameters such as density, molar volume, electronegativity, optical basicity and refractive index were calculated. The non-crystalline nature of the samples was confirmed by XRD analysis. SEM images projected that the prepared glass materials were contain well defined and indiscriminately allocated grains. The chemical analysis of these materials was studied by energy dispersion spectrum. The glass transition and glass crystallization temperatures of the glasses were recorded by DTA. FT-IR, Raman and ESR studies were also carried out on the prepared glass samples. The optical absorption reports of these glass materials have suggested that the octahedral tendency of Mn2+ ions increases with increasing concentration of MnO. The optical bandgap, Urbach energy, transition probability and emission cross section of these glass materials were calculated. Photoluminescence studies were also performed on the glass samples. The outcomes on all the investigations of these glasses have suggested that the Mn2+ ions predominantly occupy octahedral sites at higher concentrations of MnO.

Fabrication and measurement of optical and spectral properties of the transparent Yb:MgAl2O4 ceramics

In this paper results concerning the fabrication of transparent (with 0.1% mol Yb3+), translucent (with 0.5% mol Yb3+) and opaque (up to 5% mol Yb3+) Yb3+: MgAl2O4 ceramics by hot pressing are presented. The alkoxotechnology of starting magnesium aluminate spinel nanopowder synthesis with homogeneous distribution of Yb ions is proposed. The structural properties of the prepared powders and ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET method. The optical transmittance, absorption and emission cross sections, and the upper level lifetime of the Yb3+:MgAl2O4 ceramics were measured.

On interlayer stability and high-cycle simulator performance of diamond-like carbon layers for articulating joint replacements.

Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the orthopaedic field, layer performance, stability and adhesion in physiologically relevant setups are crucial and not consistently investigated. In vitro wear testing as well as adequate corrosion tests of interfaces and interlayers are of great importance to verify the long term stability of DLC coated load bearing implants in the human body. DLC coatings were deposited on articulating lumbar spinal disks made of CoCr28Mo6 biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer, tantalum films were deposited by magnetron sputtering. Wear tests of coated and uncoated implants were performed in physiological solution up to a maximum of 101 million articulation cycles with an amplitude of ±2° and −3/+6° in successive intervals at a preload of 1200 N. The implants were characterized by gravimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and cross section scanning electron microscopy (SEM) analysis. It is shown that DLC coated surfaces with uncontaminated tantalum interlayers perform very well and no corrosive or mechanical failure could be observed. This also holds true in tests featuring overload and third-body wear by cortical bone chips present in the bearing pairs. Regarding the interlayer tolerance towards interlayer contamination (oxygen), limits for initiation of potential failure modes were established. It was found that mechanical failure is the most critical aspect and this mode is hypothetically linked to the α-β tantalum phase switch induced by increasing oxygen levels as observed by X-ray diffraction (XRD). It is concluded that DLC coatings are a feasible candidate for near zero wear articulations on implants, potentially even surpassing the performance of ceramic vs. ceramic.

Europium doping in KLu(WO4)2

Europium single doped potassium lutetium tungstate Eu3+:KLu(WO4)2 single crystals have been grown with an active ion doping concentration from 0.5 to 5at% using the top seeded solution growth slow cooling method. The experimental parameters for growing these single crystals have been optimized. Optical absorption and emission cross section were subjected to a detailed spectroscopic study. 58 sublevels were determined. Red visible emission was observed and attributed to the pure electronic transition under UV laser pumping. The CIE coordinates were (0.59,0.35) with 604nm as the dominant wavelength and 84% of purity.

Argon 420.1–419.8 nm emission line ratio for measuring plasma effective electron temperatures

We explore the feasibility of using the ratio of two argon emission line intensities at 420.1 and 419.8 nm to measure the effective electron temperature in argon-containing plasmas. Experimental measurements in numerous plasma sources reveal the ratio varies from a value of approximately 1 at high electron temperatures, to a value near 4 at low electron temperatures. This variation is understood in terms of the magnitudes of the electron excitation cross sections into the upper energy levels of the two transitions. At high electron temperatures, the upper levels of the two emission lines, the J = 3 3p9 level for the 420.1 nm line and the J = 0 3p5 level for the 419.8 nm line, are both primarily populated by excitation from the ground state and have similar optical emission cross sections. At low electron temperatures, excitation is dominated by excitation from the metastable levels which have very different cross sections into the two levels. Temperatures obtained with this line pair ratio in an inductively coupled plasma are found to be consistent with values obtained from a Langmuir probe as well as an analysis of the entire set of 2px → 1sy emission lines (665–1150 nm) under a wide variety of plasma conditions.

Excitation of the 3p 55p levels of argon from the 3p 54s metastables

Measurements have been reported recently of cross sections for electron-impact excitation of the argon 3p 55p manifold of levels from the 3p 54s metastable levels. We report results of calculations of the direct excitation cross sections at electron-impact energies from threshold to 500 eV for these transitions. The collision cross sections are calculated in the scaled plane-wave Born approximation (scaled PWB) developed by Kim. This scaling transforms the Born cross sections for dipole-allowed and spin-allowed excitations into reliable cross sections that compare as well with accurate measurements as does the sophisticated and more complex convergent close coupling method. We have used jj coupling in a single LS configuration Dirac-Fock calculation to describe the target wavefunctions. The optical emission cross section measurements, by Jung et al., include estimated contributions of 25% or more from cascading from higher excited levels and so are larger than direct excitation cross sections. Nevertheless, our cross sections agree reasonably well with the measurements for transitions where the core j value remains unchanged, except for the 1s 5–3p 8 excitation. The results do not agree well with the measurements when the core j value changes, as similarly seen in the results of recent relativistic distorted wave calculations by Sharma et al.

Electron-impact excitation of argon: Optical emission cross sections in the range of 300–2500 nm

We present measurements of optical emission cross sections for excitation from the ground state of the Ar atom into over 185 excited atomic and ionic levels. Measurements were made at electron energies of 25, 50, and 100 eV, at a gas pressure of 5 mTorr. Due to radiation trapping of resonance levels, many of the cross sections depend on the target pressure. Detailed pressure dependence for over 50 levels is also provided. The energy dependence of the excitation cross sections for over 175 levels in the energy range of 0–250 eV are provided as fitted parameters for a standard analytical function.

Optical absorption intensity analysis and emission cross sections for the intermanifold and the inter-Stark transitions of Nd3+(4f3) in polycrystalline ceramic Y2O3

Spectroscopic properties have been characterized for trivalent neodymium doped polycrystalline ceramic ytttria, Nd3+:Y2O3. The Judd-Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] analysis has been applied to the room temperature absorption spectrum to determine the radiative decay rates and branching ratios of Nd3+ transitions from the F3∕24 metastable manifold to the IJ4 lower-lying multiplet manifolds. The quantum efficiency is determined from the measured fluorescence lifetime and the radiative lifetime of the F3∕24 manifold state. In addition, a detailed characterization of the Stark energy levels of the I9∕24 and I11∕24 manifolds has been performed using the room temperature fluorescence spectra for the F3∕24→I9∕24 and F3∕24→I11∕24 transitions of Nd3+(4f3) in ceramic Y2O3. The emission cross sections of the F3∕24→I9∕24 and F3∕24→I11∕24 intermanifold transitions have been determined. Also, the peak emission cross sections of the principal inter-Stark peak transitions R1→X5 and R1→Y2 have been determined. Finally, the spectroscopic properties of ceramic Nd3+:Y2O3 are compared with those of ceramic Nd3+:YAG as well as single crystals of Nd3+:Y2O3 and Nd3+:YAG.

Continuous-wave diode-pumped Yb:glass laser with near 90% slope efficiency

Room temperature highly efficient laser action from an ytterbium-doped phosphate glass is demonstrated when end pumped by a 975nm fiber-coupled laser diode. Laser slope efficiencies as high as 88% have been obtained, leading to pump-to-laser conversion efficiencies greater than 50%. From the analysis of pumping threshold and laser slope efficiencies the authors have determined both the optical losses and emission cross section at laser wavelength (1028nm).

Electron-impact excitation cross sections of the higher argon3p5np(n=5,6,7)levels

We have measured the electron-impact excitation cross sections for argon into the ten levels of ${3p}^{5}5p$ configuration, as well as numerous levels of the ${3p}^{5}6p$ and ${3p}^{5}7p$ configurations. Fluorescence from the decay of the excited atoms to the levels of ${3p}^{5}4s$ configuration was used to determine the optical-emission cross sections. These results were combined with transition probabilities to find apparent cross sections into the ${3p}^{5}5p$ and ${3p}^{5}6p$ levels. These new cross sections of the $\mathrm{Ar}{(3p}^{5}np)$ levels along with the available $\mathrm{Ne}{(2p}^{5}3p),$ $\mathrm{Kr}{(4p}^{5}5p),$ and $\mathrm{Xe}{(5p}^{5}6p)$ data help provide a global view of the excitation behaviors of the ${\mathrm{np}}^{5}{n}^{\ensuremath{'}}p$ levels of the rare-gas series.

Excitation transfer cross sections for levels of the Ne2p53dconfiguration

We have measured electron-impact optical emission cross sections for selected resonance and nearby nonresonant levels of the neon ${2p}^{5}3d$ configuration at pressures from 2 to 70 mTorr. The enhanced fluorescence observed from nonresonant levels at high pressures is consistent with excitation transfer from highly populated resonance levels of the ${2p}^{5}3d$ configuration. We measured excitation-transfer cross sections of $540\ifmmode\pm\else\textpm\fi{}80 {\mathrm{\AA{}}}^{2},$ $1600\ifmmode\pm\else\textpm\fi{}500 {\mathrm{\AA{}}}^{2}$, and $1100\ifmmode\pm\else\textpm\fi{}200 {\mathrm{\AA{}}}^{2}$ for transfer from the ${3d}_{5}\ensuremath{\rightarrow}{3d}_{6},$ ${3s}_{1}^{\ensuremath{'}}\ensuremath{\rightarrow}{3s}_{1}^{\ensuremath{''}},$ and ${3s}_{1}^{\ensuremath{'}}\ensuremath{\rightarrow}{3s}_{1}^{}$, respectively.

Electron-impact excitation of nitric oxide(A2Σ+–X2Π)

We report absolute optical emission cross sections for 31 vibrational transitions of the A 2 Σ + (v')-X 2 ∏(v) system of nitric oxide for electron-impact energies from threshold to 740 eV using the optical method and a crossed-beam geometry. Our measurements include emission bands originating in the v'=0, 1, 2, 3 vibrational levels and terminating in the v levels from 0 up to 11. We find good agreement between our emission cross sections, our measurements of the emission intensities from an rf discharge, and the intensities predicted by the Franck-Condon principle. We also obtain apparent level cross sections for the v'=0, 1, 2, 3 vibrational levels of the A 2 Σ + state; despite the presence of a cascade, these level cross sections are proportional to the direct excitation rates predicted by the Franck-Condon principle. We determine the total apparent cross section for the A 2 Σ electronic state to reach its peak value of 40X 10 - 1 9 cm 2 at 30 eV.

Use of radiation trapping for measuring electron-impact excitation cross sections for higher resonance levels of rare-gas atoms

Radiation trapping causes the optical emission cross sections for transitions from an atomic resonance level to lower levels to be dependent on the atom number density. We have measured the optical emission cross sections for a number of heavy rare-gas resonance transitions over the pressure range of 0.04 to 30 mTorr. We compare the results with the theory of Heddle, using it to extrapolate our cross-section data to the high-pressure regime where the resonance radiation is completely reabsorbed. This allows us to obtain the apparent excitation cross section for seven resonance levels of Ne, Ar, and Kr without measuring the resonance radiation that would otherwise entail vacuum ultraviolet radiometry. In some cases, our analysis of the measured pressure dependence of the optical emission cross sections points out the need for improved transition probabilities values.

Cross sections for electron-impact excitation of Krypton

Electron-impact excitation cross sections for Kr have been measured by means of the optical method over a range of incident-electron energies between onset and 250 eV. By measuring cascade transitions into the ${4p}^{5}5p$ levels from higher-lying levels and subtracting this contribution from the observed transitions out of the ${4p}^{5}5p$ levels, we are able to determine the cross sections for direct electron excitation into the ten levels of the ${4p}^{5}5p$ configuration $(2p$ in Paschen's notation). The general trends of these cross sections for Kr are compared with previous measurements from our labs on Ne, Ar, and Xe. We note that the optical emission cross sections for transitions from levels resonant with the ground level vary with gas pressure. Fitting this observed pressure dependence to a simple model allows us to test theoretical values of the transition coefficients for these levels.

Electron-impact excitation cross sections of neon

To determine the direct electron-impact excitation cross sections with the optical method, one must measure all transitions out of a level, as well as the cascade into the level of interest from higher-lying energy levels. Considered here are the ten levels of the ${2p}^{5}3p$ configuration of neon, whose emissions to lower levels fall within a range of 540--810 nm. This allows an investigation via a monochromator-photomultiplier tube system. Cascades into these levels from ${2p}^{5}4s$ and ${2p}^{5}3d,$ however, emit radiation in the 740--1720-nm range, part of which is outside the limit of photomultiplier detection. We employ a Fourier-transform spectrometer to examine the near-infrared lines. We report direct electron excitation cross sections for the ten ${2p}^{5}3p$ levels for electron energies up to 200 eV. In addition, we provide apparent excitation functions for the ${2p}^{5}4s$ and ${2p}^{5}3d$ levels. We have also observed a dependence of the optical emission cross sections on pressure, and describe this effect within the framework of the resonance radiation reabsorption model.

Direct experimental measurement of electron impact ionization‐excitation branching ratios: 3. Branching ratios and cross sections for the N2+X2Σg+, A2Πu, and B2Σu+ states at 100 eV

The three electronic states of N2+ which are important to aeronomy are the X 2Σg+, A 2Πu, and B 2Σu+ states. The transitions X 2Σg+ ← A 2Πu, and X 2Σg+ ← B 2Σu+ are responsible for the prominent Meinel bands and first negative bands which occur in the aurora and airglow. In this paper, we use new electron‐electron coincidence (e,2e) measurements to extend our previous work on the B 2Σu+ state cross section to give a complete set of branching ratios and cross sections for N2+ production in the three electronic states given above by 100‐eV electron impact on N2. An improved electron‐electron coincidence apparatus has allowed the direct measurement of the cross section and branching ratio for the X 2Σg+ state for the first time. The cross sections for the X and A states agree within experimental error with the existing optical excitation results in the literature, but the error bars on the present measurements are smaller than those for the optical experiments. The branching ratios for the N2+ X and A states at 100 eV are 0.448±0.033 and 0.453±0.033, respectively. The corresponding 100‐eV excitation cross sections for the X and A states deduced from the total N2+ 100‐eV electron impact ionization cross section which is known from other measurements are 86.9±7.0 × 10−18 cm2 and 87.9±7.0 × 10−18 cm2, respectively. The B state results, which have been discussed in detail in a previous paper, are branching ratio of 0.099±0.017 and excitation cross section of 19.2±3.3 × 10−18 cm2. These values are significantly lower than the result deduced from the widely accepted optical emission cross section of Borst and Zipf [1970] but in satisfactory agreement with the “best” value for the cross section of 23.6 × 10−18 cm2 previously deduced from a combination of optical and (e,2e) results.