Search

We report on the experimental observation of intrinsic photoluminescence from semiconductors in the terahertz spectral range. The intrinsic terahertz photoluminescence is caused by intraexciton radiative transitions excited during the process of the binding of nonequilibrium electrons and holes into free excitons. The experiments were carried out on high-purity Si crystals at helium temperatures and under interband photoexcitation intensities not exceeding 1W/cm². [ABSTRACT FROM AUTHOR]

• Complete datasets of excitation energies, g factors, E1, E2, M1 radiative transition properties arising from the lowest 30 energy levels of Th3+ are determined by the relativistic coupled-cluster method. • Electron correlation corrections to the energies and radiative transition properties of Th 3 + are studied in detail. • The energies of the 9 D 3 / 2 , 5 / 2 and 8 F 5 / 2 , 7 / 2 levels, a few g factors, and many transition properties of Th 3 + are reported for the first time. Energies, Landé g factors, line strengths, transition probabilities, and oscillator strengths for electric dipole (E1), electric quadrupole (E2), and magnetic dipole (M1) transitions arising from the n S 1 / 2 (n =7-10), n P 1 / 2 , 3 / 2 (n =7-9), n D 3 / 2 , 5 / 2 (n =6-9), n F 5 / 2 , 7 / 2 (n =5-8), and n G 7 / 2 , 9 / 2 (n =5,6) energy levels in Th 3 + , are calculated using the singles and doubles approximation of the relativistic coupled-cluster (CCSD) method. The data are compared with available experimental and theoretical results, showing a good agreement. To the best of our knowledge, many results are reported for the first time. This work reports a high-precision atomic property calculation of Th 3 + and is of great significance for future spectral analysis and precision experiments targeting various applications. [ABSTRACT FROM AUTHOR]

We have performed calculations for Cu-like to Br-like neodymium (Nd) ions using the multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction (RCI) approaches. An extensive set of fine structure energy levels, lifetimes, wavelengths, and radiative transitions for electric and magnetic multipole transitions is provided. We systematically include the electronic correlation effects between valence electrons and two subshells of core electrons. In the RCI procedure, both the Breit interaction and the leading quantum electrodynamic effects are taken into account. The reliability and accuracy are confirmed by comparing our results to accessible experimental and theoretical data. [ABSTRACT FROM AUTHOR]

In recent years, AIE (aggregation-induced emission) fluorophores have attracted great interest owing to their advantages in wide areas and many AIE fluorophores have be designed by combing conventional fluorophores with AIEgens that exhibiting AIE attributes. However, only few efficient AIEgens were developed. Here, novel dihydrobenzoquinolines (h-DHBQs 4a − e and f-DHBQ 5a), a new kind of AIEgens with strong AIE, are reported. DHBQs were synthesized by a catalyst-free multi-component reaction (MCR) in good overall yield and their optical properties were investigated through steady-state and transient fluorescence spectra, single-crystal diffraction, calculated HOMOs and LUMOs. It was found that DHBQs have these characteristics: a) strong AIE, that is, their fluorescence quantum yields lower than 4.1% in solutions, but high to 90.5% in crystals; b) efficient through-bond and -space conjugated nonaromatic central heterocycle; c) radiative-process-favored but non-radiative-decay-prevented self-assemblies; d) emissive excimers; and e) easily tunable fluorescence color. This work affords a new kind of AIEgens with excellent optical properties in solids and a strategy to develop AIEgens by constructing nonaromatic heterocycle using simple MCRs. Novel through-bond and -space conjugated dihydrobenzo[h]/[f]quinolines (h-DHBQs 4a − e and f-DHBQ 5a) can be synthesized by a catalyst-free multicomponent reaction (MCR) in good overall yields. Their fluorescence quantum yields are lower than 4.1% in solutions, but high to 90.5% in crystals because their self-assemblies promote radiative transition but prevent nonradiative transition. Unusually, intermolecular compact π–π stacking causes no conventional emission-quenching. [Display omitted] • Novel dihydrobenzoquinolines could be synthesized by a multicomponent reaction. • They show strong AIE with fluorescence quantum yields as high as 90.5% in crystals. • They have efficient through-space conjugated nonaromatic central heterocycles. • Their self-assemblies favor radiative decay but prevent non-radiative decay. • Formed excimers are emissive. [ABSTRACT FROM AUTHOR]

A series of thulium-doped gallium-rich germano-gallate glasses are fabricated and thoroughly investigated. Their synthesis under an atmosphere-controlled glove box allows for a low hydroxyl concentration estimated at 14 wt ppm. From X-Ray diffraction spectroscopy and differential scanning calorimetry, the vitreous state of such gallium-rich BGG composition is confirmed. A structural analysis performed via Raman spectroscopy supports a three-dimensional interconnected glass network of gallium and germanium tetrahedra stabilized by Ba2+ ions as a charge compensator. From steady-state and time-resolved spectroscopies, Judd-Ofelt analysis is applied to determine the radiative transition rates, both absorption and emission cross-sections along with the resonant energy transfer microparameters. Through laser excitation at 808 nm, the intense 1.8 μm trivalent thulium emission is observed, while no concentration quenching is detected. Hence, the present work demonstrates gallium rich-BGG glasses doped with Tm3+ are suitable systems for IR photonic applications, notably for the development of high-power IR lasers. • Successful synthesis of low-OH crystal-free gallium-rich germano-gallate glasses doped with thulium. • Steady-state and time-resolved spectroscopies of the trivalent thulium luminescence have been carried out. • Thorough Judd-Ofelt investigation has been performed. • No quenching of concentration has been reported up to 2 mol% of Tm3+. [ABSTRACT FROM AUTHOR]

Alkaline earth titanium borate glasses doped with different ratios of Er3+ ions were fabricated using standard melt quenching technique. The density of the glasses increased from 3.652 to 3.762 g/cm3 as the ratio of Er3+ ions increased from 0 to 5.640 × 1020 cm−3. The gaussian deconvolution of the Raman and FTIR spectra was investigated, and the distinctive spectral vibrational bands were assigned. The UV–Vis–NIR absorption spectra of the erbium doped glasses exhibit nine bands located at 1531, 980, 808, 654, 520, 490, 446, 408, and 377 nm due to the electronic transitions of Er3+ ions from the ground level 4I 15/2 to the higher excited levels 4I 13/2 , 4I 11/2 , 4I 9/2 , 4F 9/2 , 2H 11/2 , 4F 7/2 , 4F 3/2 , 2G 9/2 , and 4G 11/2 , respectively. The structural and luminescent properties of the erbium doped glasses were investigated by calculating Judd – Ofelt intensity parameters, radiative transition probabilities, branching ratio, lifetime, full width at half maximum (FWHM), and gain bandwidth (FWHM × σ emis). The intensity parameters followed the trend as Ω 2 > Ω 6 > Ω 4 for all glasses. The values of Ω 2 decreased from 5.2079 × 10−20 to 3.8133 × 10−20 cm2 and that of Ω 4 decreased from 0.7402 × 10−20 to 0.5939 × 10−20 cm2 as the ratio of Er3+ ions increased. The high laser efficiency of the studied glasses were verified by the high values of the radiative lifetime, branching ratio, FWHM, and gain bandwidth. The gain spectra for BaTiBEr3 and BaTiBEr5 glasses covered the conventional (1530–1565 nm) and long (1565–1625 nm) communication bands. Moreover, the high values of the FWHM and gain bandwidth for BaTiBEr3 and BaTiBEr5 glasses, suggested their suitability for photonic applications in the near infrared region and broadband optical fiber amplifiers. • Er3+- doped alkaline earth titanium borate glasses are fabricated via standard melt quenching technique. • Gaussian deconvolution of Raman and FTIR spectra is investigated, and distinctive vibrational bands are assigned. • Radiative properties of 4f – 4f electronic transitions were investigated through Judd – Ofelt theory and PL spectroscopy. • The gain spectra for BaTiBEr3 and BaTiBEr5 glasses cover the conventional and long communication bands. • BaTiBEr3 and BaTiBEr5 glasses have the potential to design erbium doped fiber amplifiers for networking applications. [ABSTRACT FROM AUTHOR]

• Erbium (Er3+) doped Sb 2 O 3 -Na 2 O-WO 3 glasses have been synthesized. • Judd-Ofelt analysis has been used to calculate the radiative transition probabilities (A rad), radiative lifetimes (τ rad), and branching ratios (β). • Broadband emission at 1.53 μm has been obtained under 980 nm laser excitation. • SN0.2WE glass has a minimum W NR value (78.14 s - 1 ) and a maximum quantum efficiency of η = 82.42 % , which is very good compared to other glass hosts. • The emission cross-section and the gain parameter (σ e m a n d F W H M × σ e m ) have considerable bandwidth characteristics higher than other glass hosts. Glasses with compositions (0.8-x)Sb 2 O 3 −0.2Na 2 O-(x)WO 3 -(0.0025) Er 2 O 3 , (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 (T g), the density (ρ) , molar volume (V m) , 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 (Δλ eff), the emission cross-section (σ em), 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 4I 13/2 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. [ABSTRACT FROM AUTHOR]

High performance blue emitters with nice color purity are highly desired in the commercialization of organic light-emitting diodes (OLEDs). Herein, two blue-emissive hybridized local and charge-transfer (HLCT) phenanthroimidazole (PPI) derivatives were designed and synthesized. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN demonstrates higher photoluminescence quantum yield (PLQY) and improved radiative transition rate (k r). With the same device structure, despite that SPCN and DPCN show similar electroluminescence (EL) spectra, the EL efficiency of SPCN is about 1.5 times that of DPCN. Especially the non-doped OLED based on SPCN , the maximum external quantum efficiency (EQE) is 7.1%, which is a competitive result among the conventional blue-emissive fluorescent emitters. More importantly, this work provides a general strategy to achieve high performance blue/deep-blue OLED by rational donor optimization. In this work, we report two blue-emissive hybridized local and charge-transfer (HLCT) materials (DPCN and SPCN) with different donor substitution. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN displays an improved EL efficiency and blue purity, which provides an ideal molecular design strategy for efficient blue/deep-blue EL materials. [Display omitted] • Two blue-emissive HLCT materials with different donor substitution were designed and synthesized. • The relationship of structure-physical property as well as OLED performance are comprehensively explored. • Comparing to DPCN, the SAF substituted SPCN achieved a better OLED performance. [ABSTRACT FROM AUTHOR]

In recent years, upconversion photoluminescent micro/nanocrystals with unique anti-Stokes luminescence properties have shown high application value in many relevant fields. In this work, pure tetragonal phase NaLa(MoO 4) 2 :Yb3+/Ho3+ microspheres have been synthesized by a solvothermal method in the presence of oleic acid and 1-octadecene. Under the excitation of 980 nm laser, NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals emit red, green and near infrared upconversion luminescence with peak wavelengths at 660/643 nm, 541 nm, and 756 nm. Based on the analysis of excitation power-dependent upconversion luminescence intensities and energy level diagram of Yb3+/Ho3+, electronic transition pathways in the energy transfer processes for upconversion luminescence of NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals are studied. For red upconversion luminescence at 660/643 nm, the predominant population pathway to state 5 F 5 (Ho3+) is "Yb3+ (2 F 5/2) + Ho3+ (5 I 7) → Yb3+ (2 F 7/2) + Ho3+ (5 F 5)". While, "Yb3+ (2 F 5/2) + Ho3+ (5 I 6) → Yb3+ (2 F 7/2) + Ho3+ (5 F 4 /5 S 2)" process accounts for the population of state 5 F 4 /5 S 2 (Ho3+) for radiative transitions of upconversion luminescence at 541 and 756 nm. Energy back transfer contributes to the intense red upconversion luminescence at 660/643 nm. These electronic transition pathways in energy transfer processes are further confirmed by the analyses based on energy level mismatch and luminescent lifetimes. [Display omitted] • Electronic transition pathways for energy transfer upconversion luminescence in NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals. • Predominant population pathway for red upconversion luminescence at 660/643 nm of Ho3+ is elucidated. • Analyses of energy level mismatch and luminescent lifetimes confirm the proposed electronic transition pathways. [ABSTRACT FROM AUTHOR]

The Er3+:YPO 4 crystals co-doped with different concentrations of Yb3+ (7.5 at.% and 11.5 at.%) were successfully grown by high-temperature solution method with Pb 2 P 2 O 7 as cosolvent. Crystal growth, structures and spectroscopic characterizations, including polarized absorption spectra, polarized fluorescence spectra and lifetime, were systematically explored and compared. The absorption FWHM at around 975 nm is 17.1 nm for σ- polarizations and 12.0 nm for π- polarizations, which makes Er3+/Yb3+:YPO 4 crystal suitable for effective pumping by InGaAs laser diode. Based on J-O theory, the spectroscopic parameters, including J-O intensity, oscillator strength, line strength, fluorescence branching ratios, spontaneous transition rates and radiative lifetime were calculated systematically. Furthermore, four intense emission peaks at around 1505, 1537, 1561 and 1586 nm can be observed in the polarized fluorescence spectra. Theoretically, different frequencies interactions between these wavelengths may be used for the application of generating radiation in the range of 2.9–10.2 THz. The results show that Er3+/Yb3+:YPO 4 crystal may be a potential laser material of 1.5–1.6 μm. [Display omitted] • The Er3+/Yb3+:YPO 4 crystal was grown successfully from Pb 2 P 2 O 7 solution. • Spectral parameters of Er3+ ions were calculated in detail based on J-O theory. • Intense multi-wavelength emissions can be observed in the range of 1.5–1.6 μm. [ABSTRACT FROM AUTHOR]

• Eight total transition probabilities were estimated for Eu, five for Eu I and three for Eu II. • The temperature and electron density of the plasma were estimated through iterative fitting of a Saha-Boltzmann plot. • This method of estimating transition probabilities promotes a broadening of the application of Calibration Free-LIBS to other lanthanides. Laser-induced breakdown spectroscopy (LIBS) is a versatile technique for compositional analysis for solids, liquids, or gasses. LIBS is an asset for the quantitative or qualitative analysis of resource limited materials like actinides and rare earths because it is quasi-nondestructive. Two Eu 2 O 3 pellets were synthesized to be a test and validation set, respectively. Spectral lines identified from the National Institute of Standards and Technology database with fundamental data reported were used to form Saha-Boltzmann plots. The Saha-Boltzmann plots were used to determine the plasma temperatures and electron densities of the laser-induced plasmas for both samples. These Saha-Boltzmann plots were then used to calculate previously unreported transition probabilities associated with identified peaks. The transition probabilities presented in this paper provide the capability for calibration free LIBS to be performed more readily on europium samples and the spectroscopic analysis of stellar bodies. Eight previously unreported transition probabilities are presented in this paper; five for Eu I and three for Eu II. The transition probabilities for Eu I ranged from 0.172 to 7.38 × 107 s−1 and those for Eu II ranged from 1.56 to 6.75 × 107 s−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • K-doped GQDs were synthesized by mechanochemical reaction for the first time. • K atoms were chemically bonded into the N and O-the so-called Lewis sites of GQDs. • K induced long wavelength fluorescence enhancement effect was demonstrated. • K-GQDs displayed benign cytocompatibility and good cellular imaging performance. The electron modification effects of alkaline metal on graphene and carbon nanotubes have been widely studied by numerous research groups, but never been explored on graphene quantum dots (GQDs), owing to the limitation of synthetic method. Here, we presented a dopant controllable mechanochemical procedure for potassium-doped GQDs (K-GQDs) preparation: by shifting the synthetic parameters, the doping degree of K can be effectively adjusted with little change of the crystal lateral size. Physiochemical characterizations revealed that the K+ tended to form chemical bonds with carbonyls, pyrrolic and graphic nitrogen-the so-called Lewis acid. Spectral techniques further confirmed the K dopants on the as-mentioned sites could reduce the blue fluorescence that related to the intrinsic state, but enhance the yellow and orange florescence caused by the increase of electron radiative transition rate between π*-n O2p and π*-n N2p simultaneously. Moreover, the K-GQDs displayed benign cytocompatibility and cellular fluorescence imaging performance. Herein, we propose the K+ may play a role in enhancing long wavelength florescence intensity of GQDs, which makes the K-GQDs a promising probe for bioimaging. To our knowledge, this is the first time to report the successful preparation of GQDs chemically doped by K element and reveal the long wavelength florescence enhancement (LWFE) effect of K doping. Our findings suggest that the alkaline metal doping may be an effective technique to overcome the florescence wavelength limitations of GQDs in bioimaging applications. [ABSTRACT FROM AUTHOR]

Simultaneous reconstruction of the radiative parameter distributions in participating media, based on the transient radiative transfer equation (TRTE), was investigated. The discrete ordinate method was employed to solve the direct TRTE for two-dimensional participating media. A multi-start iterative technique, based on the conjugate gradient (CG) method, was proposed to accelerate the convergence speed of the inverse procedure. The maximum a posteriori (MAP) estimation was used to overcome the retrieval difficulties resulting from the ill-posed nature of the inverse problem. The gradient of the objective function was obtained using adjoint differentiation. All the simulation results show that MAP combined with the multi-start iterative CG technique is effective in simultaneously reconstructing the distributions of absorption and scattering coefficients in two-dimensional inhomogeneous media, even with noisy data. [ABSTRACT FROM AUTHOR]

Radiativetransitions between the three lowest-lying electronicstates of molecular oxygen have long provided a model to study howcollision-dependent perturbations influence forbidden processes. Inan isolated oxygen molecule, transitions between the O2(X3Σg–), O2(a1Δg), and O2(b1Σg+) states are forbidden as electric-dipoleprocesses. For oxygen dissolved in organic solvents, the probabilitiesof radiative transitions between these states increase appreciably.Attempts to interpret solvent-dependent changes in the radiative rateconstants have principally relied on O2(b1Σg+) and O2(a1Δg) emission experiments. However, the dominant nonradiative deactivationchannels of O2(b1Σg+) make it difficult to quantify solvent effects on the O2(b1Σg+) → O2(a1Δg) radiative process. Thus, an appreciableamount of important information has heretofore not been available.In the present study, we examined the effect of 17 common organicsolvents on the O2(a1Δg) →O2(b1Σg+) absorptiontransition at ∼5200 cm–1(i.e., ∼1925nm). The solvent-dependent absorption coefficients at the band maximum,εmax, range from 5 to 50 M–1cm–1and correlate reasonably well with the solvent refractiveindex; εmaxis largest in solvents with the largestrefractive index. This observation is consistent with a model in whichoxygen is perturbed to a greater extent by solvents with a large electronicpolarizability. Through the Strickler–Berg equation, we alsoused these absorption data to obtain the radiative rate constant forthe O2(b1Σg+) →O2(a1Δg) transition, and theresults are consistent with a model in which the O2(a1Δg) → O2(X3Σg–) transition is said to steal intensityfrom the O2(b1Σg+) → O2(a1Δg) transition. [ABSTRACT FROM AUTHOR]

Er 3+ /Ce 3+ co-doped and B 2 O 3 modified tellurite glasses with initial composition of TeO 2 –GeO 2 –Li 2 O–Nb 2 O 5 were prepared using melt-quenching technique for potential applications in Er 3+ -doped fiber amplifiers (EDFAs) and lasers. The absorption spectra, fluorescence spectra, up-conversion spectra, Raman spectra and differential scanning calorimeter (DSC) curves of glass samples were measured to evaluate the effect of B 2 O 3 modification on the 1.53 μm band spectroscopic properties of Er 3+ , structural nature and thermal stability of glass hosts. It was shown that the introduction of an appropriate amount of B 2 O 3 oxide can further improve the 1.53 μm band fluorescence emission through an enhanced phonon-assisted energy transfer (ET) from Er 3+ to Ce 3+ ions under the excitation of 980 nm, and the quantitative studies were carried out to elucidate the ET mechanism via calculating the microscopic parameters and phonon contribution ratios. Meanwhile, the thermal stability of glass hosts increases slightly with the introduction of B 2 O 3 oxide. Furthermore, the 1.53 μm band optical signal amplification was simulated based on the rare-earth ion rate and light power propagation equations. An increment in signal gain by about 1.4 dB at 1532 nm was observed in the Er 3+ /Ce 3+ co-doped tellurite glass fiber containing 6 mol% amount of B 2 O 3 oxide, and the maximum signal gain reaches to 31 dB on a 50 cm fiber pumped at 980 nm with power 200 mW. The present results indicate that the prepared Er 3+ /Ce 3+ co-doped tellurite glass modified by an appropriate amount of B 2 O 3 oxide has good prospect as a gain medium applied for 1.53 μm band EDFAs and lasers. [ABSTRACT FROM AUTHOR]

Atomically thin two-dimensional crystals have revolutionized materials science. In particular, monolayer transition metal dichalcogenides promise novel optoelectronic applications, owing to their direct energy gaps in the optical range. Their electronic and optical properties are dominated by Coulomb-bound electron-hole pairs called excitons, whose unusual internal structure, symmetry, many-body effects and dynamics have been vividly discussed. Here we report the first direct experimental access to all 1s A excitons, regardless of momentum-inside and outside the radiative cone-in single-layer WSe2. Phase-locked mid-infrared pulses reveal the internal orbital 1s-2p resonance, which is highly sensitive to the shape of the excitonic envelope functions and provides accurate transition energies, oscillator strengths, densities and linewidths. Remarkably, the observed decay dynamics indicates an ultrafast radiative annihilation of small-momentum excitons within 150 fs, whereas Auger recombination prevails for optically dark states. The results provide a comprehensive view of excitons and introduce a new degree of freedom for quantum control, optoelectronics and valleytronics of dichalcogenide monolayers. [ABSTRACT FROM AUTHOR]

Self-Q-switching of a loop laser cavity with a self-pumped four-wave phase-conjugate mirror in an active laser medium with the use of a Faraday isolator or a passive Q-switch is studied theoretically. It is found that, in contrast to passive Q-switching of an ordinary cavity, a passive Q-switch in a loop phase-conjugate cavity serves as an auxiliary unit that increases the self-Q-switching efficiency by gain gratings in the active laser medium, since it decreases the difference in the intensities of waves that write a phase-conjugate mirror in the active medium, which is similar to the use of a Faraday isolator. However, the passive Q-switch operates alternating the highly efficient writing of a phase-conjugate mirror in the closed state with the highly efficient generation of a giant laser pulse in the open state, which stabilizes the period of repetitive laser pulses. [ABSTRACT FROM AUTHOR]

Radiative transitions occurring at atomic collisions are considered. Attention is focused on the transitions that are either impossible in individual atoms or ions or forbidden by the selection rules. The excitation of continuous-spectrum electron states is considered for the first time by an example of photodetachment at collisions of negative ions with neutral atoms. [ABSTRACT FROM AUTHOR]

Recent quantum mechanical calculations of rate coefficients for collisional transfer of population between the hyperfine states of 13CN enable their population densities to be determined. We have computed the relative populations of the hyperfine states of the N = 0, 1, 2 rotational states for kinetic temperatures 5 ≤ T ≤ 20 K and molecular hydrogen densities 1 ≤ n(H2) ≤1010 cm-3. Spontaneous and induced radiative transitions were taken into account. Our calculations show that, if the lines are optically thin, the populations of the hyperfine states, F, within a given rotational manifold are proportional to their statistical weights, (2F + 1) - i.e. in local thermodynamic equilibrium - over the entire range of densities. We have re-analysed IRAM 30 m telescope observations of 13CN hyperfine transitions (N = 1 → 0) in four starless cores. A comparison of these observations with our calculations confirms that the hyperfine states are statistically populated in these sources. [ABSTRACT FROM AUTHOR]

The photoluminescence and photoluminescence excitation spectra of SiO films implanted with high (3 at %) Si-ion doses are studied in relation to the temperature of postimplantation annealing. It is shown that two photoluminescence bands with peaks at 2.7 and 2 eV are dominant in the spectra. As the annealing temperature is increased, the relation between the intensities of the 2.7 and 2 eV bands changes in favor of the former one. Both of the photoluminescence bands have their main excitation peak at the energy 5.1 eV. The excitation spectrum of the ~2-eV band exhibits also peaks at 3.8 and 4.6 eV. It is concluded that, in the implanted SiO films, the orange photoluminescence band originates from radiative transitions between levels of centers associated with a deficiency of oxygen (≡Si-Si≡ or =Si:) and the levels of nonbridging oxygen (≡Si-O•). [ABSTRACT FROM AUTHOR]

Atomically thin two-dimensional crystals have revolutionized materials science. In particular, monolayer transition metal dichalcogenides promise novel optoelectronic applications, owing to their direct energy gaps in the optical range. Their electronic and optical properties are dominated by Coulomb-bound electron-hole pairs called excitons, whose unusual internal structure, symmetry, many-body effects and dynamics have been vividly discussed. Here we report the first direct experimental access to all 1s A excitons, regardless of momentum-inside and outside the radiative cone-in single-layer WSe2. Phase-locked mid-infrared pulses reveal the internal orbital 1s-2p resonance, which is highly sensitive to the shape of the excitonic envelope functions and provides accurate transition energies, oscillator strengths, densities and linewidths. Remarkably, the observed decay dynamics indicates an ultrafast radiative annihilation of small-momentum excitons within 150 fs, whereas Auger recombination prevails for optically dark states. The results provide a comprehensive view of excitons and introduce a new degree of freedom for quantum control, optoelectronics and valleytronics of dichalcogenide monolayers. [ABSTRACT FROM AUTHOR]

YO:Eu phosphor was deposited on quartz fibers by electron beam evaporation technology and the deposited fibers were then annealed at different rates from 1 to 10 °C/min. Particle shape of the YO:Eu deposited on fibers was changed with the increased annealing rate and the particle size was increased significantly with the rise of annealing rate to 5 °C/min. The deposited film on fibers exhibited a well cubic phase after annealing treatment and its crystallization was obviously enhanced with the increased rate. The luminescent properties of the films were markedly improved by annealing treatment and the emission intensity was increased as the rate elevated from 1 to 10 °C/min because of the increased radiative transition probability of the Eu ions. The CIE chromaticity coordinates results indicated that the films can display improved color purity of red emission after annealing treatment and the color purity of the annealed films was gradually improved as the increased treating rate. [ABSTRACT FROM AUTHOR]

We demonstrated the lasing action and remarkable reduction in long radiative lifetimes of type-II GaSb/GaAs quantum dots using a circular photonic-crystal nano-cavity with high Purcell factors. The associated enhancement in carrier recombination was surprisingly high and could even surpass type-I counterparts in similar conditions. These phenomena reveal that the type-II sample exhibited extremely low nonradiative recombination so that weak radiative transitions were more dominant than expected. The results indicate that type-II nanostructures may be advantageous for applications which require controllable radiative transitions but low nonradiative depletions. [ABSTRACT FROM AUTHOR]

In this work we perform a systematic ab initio study of the dipole moment surface (DMS) of H 2 S at various levels of theory and of its effect on the intensities of vibration–rotation transitions; H 2 S intensities are known from the experiment to display anomalies which have so far been difficult to reproduce by theoretical calculations. We use the transition intensities from the HITRAN database of 14 vibrational bands for our comparisons. The intensities of all fundamental bands show strong sensitivity to the ab initio method used for constructing the DMS while hot, overtone and combination bands up to 4000 cm −1 do not. The core-correlation and relativistic effects are found to be important for computed line intensities, for instance affecting the most intense fundamental band ( ν 2 ) by about 20%. Our recommended DMS, called ALYT2, is based on the CCSD(T)/aug-cc-pV(6+d)Z level of theory supplemented by a core-correlation/relativistic corrective surface obtained at the CCSD[T]/aug-cc-pCV5Z-DK level. The corresponding computed intensities agree significantly better (to within 10%) with experimental data taken directly from original papers. Worse agreement (differences of about 25%) is found for those HITRAN intensities obtained from fitted effective dipole models, suggesting the presence of underlying problems in those fits. [ABSTRACT FROM AUTHOR]

The asymptotic normalization coefficient (ANC) is an important quantity in the calculation of radiative width amplitudes, providing limits on the radiative width. Here we present some examples showing the connection between the ANC and radiative width. In particular, the radiative width of the E1 transition l7F(l/2-, Ex = 3.104 MeV) to l7F (l/2+,Ex, = 0.495 MeV) reported by Rolfs [Nucl. Phys. A 217, 29 (1973)] is (1.2 ±0.2) x 10-2 eV. Meanwhile the ANC for the first excited state in 17F puts a lower limit on the radiative width, which is (3.4 ± 0.50) x 10-2 eV. Such a strong disagreement between the measured radiative width and the lower limit imposed by the ANC calls for a new measurement of this radiative width. Other examples are also considered. [ABSTRACT FROM AUTHOR]

We continue the study of surface corrugations influence on the monolayer graphene local electromagnetic response in terahertz range we started earlier. The effects of radiative decay, double-valley structure of charge carriers spectrum in graphene and the “breathing” corrugated surface form induced synthetic electric fields are taken into account. To fulfill this program the generalized nonlinear self-consistent-field equation is obtained. In case of weak external alternating electric field E → e x t ( t ) = E → 0 cos ω t for the obtained equation in linear approximation on the external electric field the exact solution is found. It shows that in this case we get local induced current paths depending on the surface form z = h ( x , y ) . This theoretical result qualitatively explains the corresponding experiments with local current patterns depending on the point by corrugations influence. The induced currents formula was obtained without using fully quantum approach which is necessary for theoretical description of such phenomenon in graphene nanoribbons. Besides the formulae obtained in the present paper could become the basis of the new method of the imaging of surface corrugations form for given experimental picture of local current paths. [ABSTRACT FROM AUTHOR]

Er 3+ -doped, Er 3+ /Yb 3+ co-doped tellurite glass with and without Ag NPs were synthesized by melt-quenching method. The high resolution transmission electron microscopy (HR-TEM) and selected area electron diffractions (SAED) manifest growth of Ag NPs. The UV–vis–NIR absorption spectroscopy and fluorescence spectroscopy were measured. The optical band gap and multiphonon relaxation rate constants were calculated. The electronic band structure and local density of state (DOS) of Ag NPs are calculated. The fluorescence emission and enhancement mechanism including localized surface plasmon resonance (LSPR) and energy transfer (ET) microcosmic mechanism were discussed. The electric field distributions of Ag NPs are emulated by FDTD solutions software. Local field enhancement (LFE) induced by LSPR and lightning rod effect was found to be responsible for the fluorescence enhancement while energy transfer from Ag NPs to rare-earth was considered ignorable in the samples without photoluminescent emission. [ABSTRACT FROM AUTHOR]

Sub-Doppler resolution spectroscopy of CH 3 D has been carried out from 88.6 to 93.1 THz. Thirty transitions of the ν 1 and ν 4 bands from the low- J and K = 3 levels are observed, and the A 1 – A 2 splitting is resolved for twenty-three of the thirty transitions. The absolute frequencies are determined with a typical uncertainty of 4 kHz. The effective A 1 – A 2 splitting constant of the K = 3 levels is 2 h 3, v =0 = (1.5641 ± 0.0026) Hz for the ground vibrational state, and those of the K = 3 levels for the v 1 = 1 state and of the ( K = 2, l = −1) and ( K = 4, l = +1) levels for the v 4 = 1 state are also determined. [ABSTRACT FROM AUTHOR]

The high-resolution infrared absorption spectrum of spiropentane (C 5 H 8 ) has been measured from 200 to 4000 cm −1 , and a detailed analysis is presented for eight bands in the region from 700 to 2200 cm −1 . Two fundamental perpendicular bands were analyzed, ν 22 and ν 24 near 1050 and 780 cm −1 , respectively, along with two fundamental parallel bands, ν 14 and ν 16 near 1540 and 990 cm −1 , respectively. Two other fundamentals, ν 17 and ν 23 , are seen as intense overlapping bands near 880 cm −1 and are Coriolis-coupled, producing a complex mixture in which only P -branch transitions could be tentatively assigned for ν 17 . In addition, three binary combination bands were fit at about 1570, 2082, and 2098 cm −1 which are assigned as either 2 ν 24 or ν 5 + ν 16 in the first case, ν 4 + ν 22 in the second case, and 2 ν 22 in the latter case. The two l -type resonance constants, q + and q − , were determined for each of the two perpendicular fundamentals ν 22 and ν 24 . Those two constants were also responsible for splittings observed in the K = 3 levels of ν 24 . For the ground state the order of the split K = 2 B 1 / B 2 levels has been reversed from that reported previously, based on the measurements and assignments for the ν 24 band. Rovibrational parameters deduced from the analyses are compared with those obtained from density functional Gaussian calculations at the anharmonic level. [ABSTRACT FROM AUTHOR]

X-ray luminescence spectra of LiBO:Er glasses have been investigated in the range of 200-800 nm. It is shown that all identified peaks in the dependence I = f(λ) are due to parity-forbidden intra-configuration radiative transitions within the 4 f configuration of Er ion from excited fine-structure levels of higher lying multiplets to the ground-term level I. [ABSTRACT FROM AUTHOR]

We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in 229 Th. We review the status of the experiments that aim at a direct optical observation of this transition and outline the plans for high-resolution laser spectroscopy experiments. [ABSTRACT FROM AUTHOR]

Copyright of Sultan Qaboos University Journal for Science is the property of Sultan Qaboos University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Iron emission lines at 6.4-6.97 keV, identified with Ka radiative transitions, are among the strongest discrete features in the X-ray band. These are one of the most powerful probes to infer the properties of the plasma in the innermost part of the accretion disc around a compact object. In this paper, we present a recent Suzaku observation, 100-ks effective exposure, of the atoll source and X-ray burster 4U 1705-44, where we clearly detect signatures of a reflection component which is distorted by the high-velocity motion in the accretion disc. The reflection component consists of a broad iron line at about 6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these features are consistently fitted with a reflection model, and we find that in the hard state the smearing parameters are remarkably similar to those found in a previous XMM-Newton observation performed in the soft state. In particular, we find that the inner disc radius is Rin = 17 ± 5Rg (where Rg is the gravitational radius, GM/c²), the emissivity dependence from the disc radius is r-2.5 ± 0.5, the inclination angle with respect to the line of sight is i = 43° ± 5°, and the outer radius of the emitting region in the disc is Rout > 200Rg. We note that the accretion disc does not appear to be truncated at large radii, although the source is in a hard state at ~3 percent of the Eddington luminosity for a neutron star. We also find evidence of a broad emission line at low energies, at 3.03 ± 0.03 keV, compatible with emission from mildly ionized argon (Ar XVI-XVII). Argon transitions are not included in the self-consistent reflection models that we used and we therefore added an extra component to our model to fit this feature. The low-energy line appears compatible with being smeared by the same inner disc parameters found for the reflection component. [ABSTRACT FROM AUTHOR]

We conduct spectroscopic and theoreticalstudies of photoluminescence (PL) from Ge quantum dots (QDs) fabricatedvia colloidal synthesis. The dynamics of late-time PL exhibit a pronounceddependence on temperature and applied magnetic field, which can beexplained by radiative decay involving two closely spaced, slowlyemitting exciton states. In 3.5 nm QDs, these states are separatedby ∼1 meV and are characterized by ∼82 μs and∼18 μs lifetimes. By using a four-band formalism, wecalculate the fine structure of the indirect band-edge exciton arisingfrom the electron–hole exchange interaction and the Coulombinteraction of the Γ-point hole with the anisotropic chargedensity of the L-point electron. The calculationssuggest that the observed PL dynamics can be explained by phonon-assistedrecombination of excitons thermally distributed between the lower-energy“dark” state with the momentum projection J= ± 2 and a higher energy “bright” state with J= ± 1. A fairly small difference between lifetimesof these states is due to their mixing induced by the exchange termunique to crystals with a highly symmetric cubic lattice such as Ge. [ABSTRACT FROM AUTHOR]

The area of contact between two objects was detected by using the strong enhancement of the fluorescence of rigidochromic probe molecules attached to one of the surfaces. Confinement of the molecules suppresses nonradiative decay and turns on the fluorescence. The approach is demonstrated by imaging of the contact area of a plastic sphere in contact with a flat glass surface. Our results agree excellently with the prediction of Hertz's classical theory based on elastic deformation. [ABSTRACT FROM AUTHOR]

Within the validity of perturbation theory an analytic expression for energy of an electromagnetic pulse with a Gaussian envelope absorbed on an excited inhomogeneously broadened transition is derived and subsequently analyzed. A dependence of the absorbed energy on the pulse duration and relative detuning of its carrier frequency from the central frequency of the transition is analyzed. The range is determined of the problem parameters for which nonlinearity of the considered problem is most pronounced. [ABSTRACT FROM AUTHOR]

The probabilities of the electric-dipole transitions 3 d4 p, 3 d4 f-3 d, 3 d4 s, and 3 d4 d in the spectra of nickel-like ions Kr IX, Sr XI, Y XII, Ru XVII, Pd XIX, and Ag XX are calculated semiempirically with the use of published energy levels. [ABSTRACT FROM AUTHOR]

We investigated the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material using low-temperature, power-dependent (77 K), and temperature-dependent photoluminescence (PL) measurements. Two bound-excitonic radiative transitions related to grain size inhomogeneity were identified. Both transitions led to PL spectra broadening as a result of concurrent blue and red shifts of these excitonic peaks. The red-shifted bound-excitonic peak dominated at high PL excitation led to a true-green wavelength of 553 nm for CH3NH3PbBr3 powders that are encapsulated in polydimethylsiloxane. Amplified spontaneous emission was eventually achieved for an excitation threshold energy of approximately 350 μJ/cm². Our results provide a platform for potential extension towards a true-green light-emitting device for solid-state lighting and display applications. [ABSTRACT FROM AUTHOR]

The atmospheric circulation controls how global climate change will be expressed regionally. Substantial circulation changes are expected under global warming, including a narrowing of the intertropical convergence zone, a slow down and poleward expansion of the tropical circulation, and a poleward shift of mid-latitude stormtracks and jets. Yet, climate model projections of the circulation response to climate change remain uncertain. Here we present simulations with two different aquaplanet climate models and analyse these simulations using the cloud and water-vapour locking method. We find that radiative changes of clouds and water vapour are key to the regional response of precipitation and circulation to global warming. Model disagreement in the response of key characteristics of the atmospheric circulation-the intertropical convergence zone, the strength of the Hadley circulation, and the trade winds-arises from disagreement between the models in radiative changes of tropical ice clouds and their coupling to the circulation. We find that cloud changes amplify a poleward shift of the extratropical jet, whereas water vapour changes oppose such a shift, but the degree of compensation is model-dependent. We conclude that radiative changes of clouds and water vapour are not only integral to the magnitude of future global-mean warming but also determine patterns of regional climate change. [ABSTRACT FROM AUTHOR]

Wave functions describing the state of an electron in the image potential field near the surface of a metal are obtained. General relationships for the stimulated absorption probabilities are derived in the first order of perturbation theory in the interaction of the electron with an electromagnetic wave in the dipole approximation. The probabilities of bound-bound and bound-free transitions are expressed in terms of elementary functions. Calculated matrix elements for a number of transitions are presented and the asymptotic behavior of probabilities is examined. [ABSTRACT FROM AUTHOR]

The higher altitude regions of Himalayas and Tibetan Plateau are influenced by the dust and black carbon (BC) aerosols from the emissions and long-range transport from the adjoining areas. In this study, we present impacts of advection of polluted air masses of natural and anthropogenic emissions, on aerosol optical and radiative properties at Manora Peak (~ 2000 m amsl) in central Himalaya over a period of more than two years (February 2006–May 2008). We used the most updated and comprehensive data of chemical and optical properties available in one of the most climatically sensitive region, the Himalaya, to estimate atmospheric radiative forcing and heating rate. Aerosol optical depth (AOD) was found to vary from 0.04 to 0.45 with significantly higher values in summer mainly due to an increase in mineral dust and biomass burning aerosols due to transport. In contrast, single scattering albedo (SSA) varied from 0.74 to 0.88 with relatively lower values during summer, suggesting an increase in absorbing BC and mineral dust aerosols. As a result, a large positive atmospheric radiative forcing (about 28 ± 5 Wm − 2 ) and high values of corresponding heating rate (0.80 ± 0.14 Kday − 1 ) has been found during summer. During the entire observation period, radiative forcing at the top of the atmosphere varied from − 2 to + 14 Wm − 2 and from − 3 to − 50 Wm − 2 at the surface whereas atmospheric forcing was in the range of 3 to 65 Wm − 2 resulting in a heating rate of 0.1–1.8 Kday − 1 . [ABSTRACT FROM AUTHOR]

This work deals with the radiative properties of personal protective clothings worn during firefighting operations by firemen. Several intervention jackets are tested coming from different Fire and Rescue Services in France. The present study focuses on the spectral absorptivity of these equipments over visible–IR domains. The spectral absorptivity in the IR range is mainly responsible for the conversion of radiative transfer coming from the flame into heat flux through the protective jacket. This work shows that the mean absorptivities of different equipments are high, close to 90%, which penalizes the thermal protection. This study demonstrates that the colored textile has a weak effect on the radiative properties and then on the thermal protection. On the contrary, the dyeing mode can decrease the absorptivity, hence improving the thermal protection of jackets, a dyed jacket being more efficient in the present test than a jacket made of fibers dyed before weaving. Finally, this paper presents mean absorptivities based on Planck's averages for reference temperatures between 800 K and 1400 K, allowing to compare different personal protective clothings. [ABSTRACT FROM AUTHOR]

The Photoionization, Electron -ion recombination and Radiative Processes of He and Ne rare gas atoms are investigated using the fully relativistic R-matrix method. These processes are fundamental atomic processes in astrophysical plasmas. In most existing astrophysical models these atomic data are from methods that do not sufficiently consider the level of complexity attributable to the large number of autoionizing resonances that manifest themselves in the photoionization cross-sections and, consequently, in the inverse process of (electron-ion) recombination. The Dirac Atomic R-matrix Code has been extended from low-energy electron scattering to handle bound states, photoionization and radiative recombination. In the relativistic R-matrix calculations, the sequare integrable orbitals are obtained from the multiconfiguration Dirac-Fock method by using GRASP code, where in this method, an atomic state is approximated by a linear combination of configuration state functions of the same symmetry. The configuration state functions are antisymmetrized products of a common set of orthonormal orbitals which are optimized on the bases functions of Dirac-Coulomb Hamiltonian. This basis is used to obtain bound orbitals from which the target ions are constructed in DARC code. Further relativistic contributions to the atomic states due to Breit interactions are added by diagonalizing the Dirac-Coulomb-Breit Hamiltonian matrix. The dominant quantum electrodynamic contributions have also been included as a perturbation. Calculations have been performed on He and Ne rare gas atomic systems, where good agreement is obtained between the results in this paper with the results of others. [ABSTRACT FROM AUTHOR]

The integrated intensities of a few bands in the vibrational structure of the astrophysically significant A Σ−X Σ and A Π−X Σ systems of barium monoxide (BaO) have been measured experimentally using band spectra. The radiative transition parameters such as Franck-Condon (FC) factor, r-centroid, electronic transition moment, Einstein coefficient, band oscillator strength, radiative life time and effective vibrational temperature have been computed for A Σ−X Σ and A Π−X Σ systems of BaO molecule by the more reliable numerical integration procedure for the experimentally known vibrational levels using Rydberg-Klein-Rees (RKR) potential energy curves. The effective vibrational temperatures of these band systems of BaO molecule are found to be nearly 3100 °K. Hence, the radiative transition parameters help us to ascertain the presence of BaO molecule in the interstellar medium and S-stars. [ABSTRACT FROM AUTHOR]

The electric dipole transitions of excited ions moving slowly in plasmas are studied. The results show that some transitions forbidden for excited ions at rest become allowed for moving excited ions. The transition rates change with varying speed of the ions. Forbidden transitions are strongly influenced by the speed, non-forbidden transitions are weakly influenced. [ABSTRACT FROM AUTHOR]

Though H 2 CO, H 2 CS, H 2 CCC, H 2 CCCC, H 2 CCO have been identified in cool interstellar molecular clouds, identification of H 2 CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H 2 CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H 2 CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q ( L , M , M ′ | E ) as a function of energy E of the colliding partner. After averaging the parameters q ( L , M , M ′ | E ) over a Maxwellian distribution, the parameters Q ( L , M , M ′ | T ) as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated. We have also calculated radiative transition probabilities for the transitions between the rotational levels. Finally, for ortho-H 2 CC, we have solved a set of statistical equilibrium equations coupled with the equations of radiative transfer and found that the H 2 CC may be identified through anomalous absorption of its transition 1 11 – 1 10 at 4.89 GHz. [ABSTRACT FROM AUTHOR]

Energy levels and radiative rates are reported for transitions in Br-like tungsten, W XL, calculated with the general-purpose relativistic atomic structure package ( grasp ). Configuration interaction (CI) has been included among 46 configurations (generating 4215 levels) over a wide energy range up to 213 Ryd. However, for conciseness results are only listed for the lowest 360 levels (with energies up to ∼43 Ryd), which mainly belong to the 4s 2 4p 5 ,4s 2 4p 4 4d,4s 2 4p 4 4f,4s4p 6 ,4p 6 4d,4s4p 5 4d,4s 2 4p 3 4d 2 , and 4s 2 4p 3 4d4f configurations, and provided for four types of transitions, E1, E2, M1, and M2. Comparisons are made with existing (but limited) results. However, to fully assess the accuracy of our data, analogous calculations have been performed with the flexible atomic code, including an even larger CI than in grasp . Our energy levels are estimated to be accurate to better than 0.02 Ryd, whereas results for radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions. [ABSTRACT FROM AUTHOR]

Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic atomic structure package ( grasp ) adopted for the calculations. Since no other results of comparable complexity are available, calculations have also been performed with the flexible atomic code ( fac ), which help in assessing the accuracy of our results. Energies are listed for the lowest 400 levels (with energies up to ∼98 Ryd), which mainly belong to the 3s 2 3p 5 , 3s3p 6 , 3s 2 3p 4 3d, 3s 2 3p 3 3d 2 , 3s3p 4 3d 2 , 3s 2 3p 2 3d 3 , and 3p 6 3d configurations, and radiative rates are provided for four types of transitions, i.e. E1, E2, M1, and M2. Our energy levels are assessed to be accurate to better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions. [ABSTRACT FROM AUTHOR]

Judd–Ofelt (J–O) theory has been applied to a series of LiLa 1− x Eu x (PO 3 ) 4 ( x = 5%; 10%; 15%; 20% and 30%) polycrystalline powders based on their emission spectra. J–O intensity parameters Ω λ ( λ = 2, 4) and various radiative properties such as the radiative transition probability ( A ), radiative life time ( τ R ), branching ratio ( β R ) and stimulated emission cross-section ( σ e ) have been determined. The observed trend for J–O parameters ( Ω 2 < Ω 4 ) reveals the ionic character of La(Eu)–O bond as well as the symmetry environment around the Eu 3+ ion in LiLa(PO 3 ) 4 . The experimental decay curves of the 5 D 0 level in LiLa 1− x Eu x (PO 3 ) 4 have a single exponential profile. The registered long life time, low multiphonon relaxation rates ( W NR ), high quantum efficiency ( η ) and the best optical gain parameter ( σ e x τ exp ) have been discussed as function of Eu 3+ concentration, chemical composition and crystal structure of the host matrix and particle-size distribution. A comparative study reveals that LiLa 1− x Eu x (PO 3 ) 4 is promising for use in optical devices as well as for developing visible red lasers to emit at 613 nm. The optical band gap energies of LiLa 1− x Eu x (PO 3 ) 4 have been calculated from the diffuse reflection spectral measurements. The results were discussed as a function of Eu 3+ concentration and compared to reported theoretical results. [ABSTRACT FROM AUTHOR]