Search

Spectroscopic studies of Ho3+-doped SrF2 crystals were performed regarding applications in solid-state lasers. The crystal structure of the Ho:SrF2 crystal was investigated using single-crystal X-ray diffraction. SrF2 exists as a cubic structure with an Fm3m space group. A Raman shift of 288 cm–1 was observed for the Ho:SrF2 single crystal. SrF2 hosts with low-frequency vibrational modes are suitable for reducing nonradiative emissions while maximizing radiative emissions. The absorption spectrum was recorded in the visible region from 400 to 800 nm, yielding absorption lines at 416, 450, 468, 473, 484, 536, 638, and 643 nm. The fluorescence spectrum recorded at an excitation wavelength of 450 nm shows two emission bands at 546 and 656 nm, which correspond to green and red emission, respectively. The intensity parameters Ωλ (λ = 2, 4, and 6) were estimated using the Judd–Ofelt theory. For Ho:SrF2 single crystal, the calculated Ωλ are Ω2 = 0.14 × 10–20 cm2, Ω4 = 3.14 × 10–20 cm2, and Ω6 = 3.74 × 10–20 cm2. The radiative transition probabilities, radiative lifetimes, and branching ratios βR for Ho:SrF2 were determined using the Judd–Ofelt parameters. The 5S2 + 5F4 → 5I8 transition is more effective for population-building processes because of its lifetime (0.26 ms) and higher branching ratios (~82.86%). Ho:SrF2 is, therefore, a promising solid-state laser crystal for green and red spectral regions. [ABSTRACT FROM AUTHOR]

The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range ~0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed. [ABSTRACT FROM AUTHOR]

A glass composition using TeO2-K2TeO3-Nb2O5-BaF2 co-doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 was successfully fabricated. Its thermal stability and physical parameters were studied, and luminescence spectroscopy of the fabricated glasses was conducted. The optical band gap, Eopt, decreased from 2.689 to 2.663 eV following the substitution of Ho2O3 with Yb2O3. The values of the refractive index, third-order nonlinear optical susceptibility (χ(3)), and nonlinear refractive index (n2) of the fabricated glasses were estimated. Furthermore, the Judd–Ofelt intensity parameters Ω t   (t = 2 , 4 , 6) , radiative properties such as transition probabilities (Aed), magnetic dipole-type transition probabilities (Amd), branching ratios (β), and radiative lifetime (τ) of the fabricated glasses were evaluated. The emission cross-section and FWHM of the 4I13/2→4I15/2 transition around 1.54 μm of the glass were reported, and the emission intensity of the visible signal was studied under 980 nm laser excitation. The material might be a useful candidate for solid lasers and nonlinear amplifier devices, especially in the communications bands. [ABSTRACT FROM AUTHOR]

We considered the radiative transition of an electron due to its spin-flip in a constant background field of the quasielectric type, which models the Lorentz-noninvariant vacuum. The power and probability of radiation and the degree of its linear polarization are calculated. It is shown that this radiative transition leads to the complete polarization of the initially unpolarized electron beam. The investigated effects increase with increasing electron energy. [ABSTRACT FROM AUTHOR]

The single crystals of CsI-Yb2+ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb2+ is due to 5d–4f transitions in Yb2+ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb2+ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb2+ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb2+ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb2+ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors. [ABSTRACT FROM AUTHOR]

Nowadays, the application scenarios of rare earth doped luminescent materials tend to be refined and complicated. The optical properties of rare earth doped materials are difficult to precisely control via the traditional design and synthesis methods, namely, changing doping concentration or preparative conditions. The aim of this study is to tune the optical transition properties of Er3+ in tungsto-molybdate NaY(Mo x W 1- x O 4) 2 (x = 0, 0.01, 0.1, 0.3, 0.5, 0.7, 0.9, 0.99 and 1.0) phosphors by changing the host matrix. The Er3+ doped continuous tungsto-molybdate solid solution NaY(Mo x W 1- x O 4) 2 phosphors were prepared via a solid state reaction technique at optimized calcination temperatures. The refractive indexes of the obtained solid solution samples were confirmed according to different models and compared. Subsequently, the optical transition intensity parameters, radiative transition rates and intrinsic radiative lifetimes of Er3+ in these solid solution phosphors were calculated in the framework of Judd-Ofelt theory. It was confirmed that the optical transition properties of Er3+ can be greatly tuned by the solid solution composition, and the tuning effects for different transitions are different. To validate the reliability of the Judd-Ofelt calculations, the temperature-dependent emission spectra of two green emissions of Er3+ for different solid solution samples were studied. It was found that the radiative transition rate ratios between two green emissions derived from theoretical calculations and experimental measurements are in reasonable agreement, thus proving that the optical transition calculations are reliable and the optical transition properties of Er3+ in the tungsto-molybdates can be tuned in a large range. This work reminds us of a new route for developing novel luminescence materials based on practical demands. [ABSTRACT FROM AUTHOR]

The broad emission bump in the electromagnetic spectra observed following the detection of gravitational waves created during the kilonova event of the merging of two neutron stars in August 2017, named GW170817, has been linked to the heavy elements of lanthanides (Z = 57–71) and a new understanding of the creation of heavy elements in the r-process. The initial spectral emission bump has a wavelength range of 3000–7000 Å, thus covering the region of ultraviolet (UV) to optical (O) wavelengths, and is similar to those seen for lanthanides. Most lanthanides have a large number of closely lying energy levels, which introduce extensive sets of radiative transitions that often form broad regions of lines of significant strength. The current study explores these broad features through the photoabsorption spectroscopy of 25 lanthanide ions, Ho I-III, Er I-IV, Tm I-V, Yb I-VI, and Lu I-VII. With excitation only to a few orbitals beyond the ground configurations, we find that most of these ions cover a large number of bound levels with open 4 f orbitals and produce tens to hundreds of thousands of lines that may form one or multiple broad features in the X-ray to UV, O, and infrared (IR) regions. The spectra of 25 ions are presented, indicating the presence, shapes, and wavelength regions of these features. The accuracy of the atomic data used to interpret the merger spectra is an ongoing problem. The present study aims at providing improved atomic data for the energies and transition parameters obtained using relativistic Breit–Pauli approximation implemented in the atomic structure code SUPERSTRUCTURE and predicting possible features. The present data have been benchmarked with available experimental data for the energies, transition parameters, and Ho II spectrum. The study finds that a number of ions under the present study are possible contributors to the emission bump of GW170817. All atomic data will be made available online in the NORAD-Atomic-Data database. [ABSTRACT FROM AUTHOR]

Previously reported atomic data (spectral lines, wavelengths, energy levels, and transition probabilities) were collected and systematically analyzed for Cs VI. The present theoretical analysis was supported by extensive calculations made for Cs VI with a pseudo-relativistic Hartree–Fock (HFR) method together with the superposition of configuration interactions implemented in Cowan's codes. In this work, all previously reported energy levels and their (allowed) transition assignments were confirmed. A critically evaluated set of optimized energy levels with their uncertainties, observed and Ritz wavelengths along with their uncertainties, and theoretical transition probabilities with their estimated uncertainties were presented in the compilation. In addition to this, we determined the radiative transition parameters for several forbidden lines within the ground configuration 5 s 2 5 p 2 of Cs VI. [ABSTRACT FROM AUTHOR]

Full utilization of the excited species at both singlet states (1R*) and triplet states (3R*) is crucial to improving electrochemiluminescence (ECL) efficiency but is challenging for organic luminescent materials. Here, an aggregation‐induced delayed ECL (AIDECL) active organic dot (OD) containing a benzophenone acceptor and dimethylacridine donor is reported, which shows high ECL efficiency via reverse intersystem crossing (RISC) of non‐emissive 3R* to emissive 1R*, overcoming the spin‐forbidden radiative decay from 3R*. By introducing dual donor‐acceptor pairs into luminophores, it is found that nonradiative pathway could be further suppressed via enhanced intermolecular weak interactions, and multiple spin‐up conversion channels could be activated. As a consequence, the obtained OD enjoys a 6.8‐fold higher ECL efficiency relative to the control AIDECL‐active OD. Single‐crystal studies and theoretical calculations reveal that the enhanced AIDECL behaviors come from the acceleration of both radiative transition and RISC. This work represents a major step towards purely organic, high‐efficiency ECL dyes and a direction for the design of next‐generation ECL dyes at the molecular level. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analysis of emission in erbium-doped and erbium and ytterbium co-doped fluoroindate glasses has been presented. The luminescence of the erbium transitions and the effect of ytterbium co-doping under 488, 808 and 976 nm laser excitation have been discussed. Optimization of rare-earth (RE) ions doping concentration and the energy transfer processes related to the sensibilization effect in Er3+/Yb3+ co-doped fluoroindate glasses focusing on the reciprocal distribution of radiative transitions, energy transfer parameters, and lifetimes have been analyzed. The luminescence consists of several bands in the visible (525, 546 and 660 nm) and the infrared (1550 and 2700 nm) spectral regions that correspond to characteristic radiative energy transitions within the erbium ions. In glasses co-doped with the Er3+/Yb3+ system, an augmentation in the emission intensity was observed in the visible and at 1550 nm, while a decrease was observed in the 2700 nm infrared band. The increase of the Yb3+: 2F 5/2 lifetime under 488, 808 and 976 nm excitation showed significant Er3+: 4I 11/2 → Yb3+: 2F 5/2 back energy transfer. Based on the analysis of the available literature, it can be concluded that energy transfer upconversion and cooperative energy upconversion play a significant role in modulating luminescence intensity values within the examined emission bands. This effect is likely enhanced due to the incorporation in a low phonon energy glass matrix. As a result of the above optimization, a glass optical fiber co-doped with 0.8 YbF 3 /1.4 ErF 3 (in mol%) was drawn and characterized, showing a strong emission at 2.77 μm. The optimized Er3+/Yb3+ co-doped fluoroindate glass and glass optical fiber confirmed their ability to be used in the visible and near-infrared spectral regions as efficient optical fiber sources. [ABSTRACT FROM AUTHOR]

The combustion method was used to synthesize Ce3+ doped LaB 3 O 6 phosphors in a range of dopant concentrations. Both the un-doped and Ce3+ doped LaB 3 O 6 samples matched the required reference card, according to X-ray diffraction patterns. TL glow curves of Ce3+ doped LaB 3 O 6 samples at various dopant concentrations were examined by employing various optical detection filter combinations to define TL characteristics. LaB 3 O 6 :Ce3+ (1%) and IRSL-TL 565 nm were selected as the suitable sample and appropriate detection filter pairing. The TL maximum with a higher intensity was seen during preheating trials (with 2 °Cs−1) at around 270 °C. The experimental results showed feasible linearity (R2 = 0.998 and b = 1.054) between 5 and 1000 Gy for the dose response of LaB 3 O 6 :Ce3+ (1%). The short-term fading test was conducted at various time intervals up to a week. The findings showed that the dosimetric peak strength was almost constant for up to 5 days. However, an additional spurious maximum appeared at the higher temperature zone. Each sample showed an abnormal heating rate effect, which can be explained by localized electrons caught in the intermediate excited state, which is capable of radiative transitions via the conduction band. To find the overlapping peak numbers and determine the kinetic parameters of preheated LaB 3 O 6 :Ce3+ (1%), various heating rates, T M - T s , initial rise, and computerized glow curve deconvolution techniques were utilized. The results suggest that LaB 3 O 6 :Ce3+ may be an appropriate material for TL dosimetry applications due to its efficient TL characteristics. [ABSTRACT FROM AUTHOR]

Crystal-field perturbation is theoretically the most direct and effective method of achieving highly efficient photoluminescence from trivalent lanthanide (Ln3+) ions through breaking the parity-forbidden nature of their 4f-transitions. However, exerting such crystal-field perturbation remains an arduous task even in well-developed Ln3+-doped luminescent nanocrystals (NCs). Herein, we report crystal-field perturbation through interstitial H+-doping in orthorhombic-phase NaMgF3:Ln3+ NCs and achieve a three-orders-of-magnitude emission amplification without a distinct lattice distortion. Mechanistic studies reveal that the interstitial H+ ions perturb the local charge density distribution, leading to anisotropic polarization of the F− ligand, which affects the highly symmetric Ln3+-substituted [MgF6]4− octahedral clusters. This effectively alleviates the parity-forbidden selective rule to enhance the 4f–4 f radiative transition rate of the Ln3+ emitter and is directly corroborated by the apparent shortening of the radiative recombination lifetime. The interstitially H+-doped NaMgF3:Yb/Er NCs are successfully used as bioimaging agents for real-time vascular imaging. These findings provide concrete evidence for crystal-field perturbation effects and promote the design of Ln3+-doped luminescent NCs with high brightness. Lanthanide-doped inorganic nanocrystals are promising for optical imaging and biomedical applications. Here authors show that interstitial H+ doping-induced crystal-field perturbation enhances the photoluminescence intensity of lanthanide-doped inorganic nanocrystals. [ABSTRACT FROM AUTHOR]

A novel vanadate host Ca2LiMg2V3O12 (CLMV) and the Eu3+‐doped samples were synthesized via a solid‐state reaction method. The phase formation and the morphological analysis were studied in detail. The Rietveld refinement result shows that the host belongs to cubic space group Ia‐3d (230) with lattice parameter, a = 12.3948 Å, V = 1904.23 Å3, and Z = 8. The diffuse reflectance spectroscopy measurement estimated the bandgap of the host and the CLMV:0.05Eu3+ phosphors. The host exhibits a broad absorption band (peak at 345 nm) ranging from 240 to 380 nm, which is attributed to the charge transfer in the O2−–V5+ complex. Under near UV excitation (λexc = 345 nm), the host gives a broad emission band covering the visible region from 400 to 730 nm and the emission is in the bluish–green region of the CIE diagram. When the host is doped with the Eu3+ ions and excited at 345 nm, the emission spectrum depicts the superimposition of the characteristic emission bands (red emission) of the Eu3+ ions corresponding to the f–f transitions over the broad emission band of the host. The calculated color coordinates (9600 to 2280 K) demonstrated the color tuning ability of the phosphor as the dopant concentration is increased in the host. This is because the VO43− group plays the sensitiser role and partially transfers energy with the Eu3+ ions. When the same set of phosphors were excited at the dominant characteristic excitation band (λexc = 394 nm) of the Eu3+, the characteristic emission bands of the Eu3+ in the orange–red region were observed. As the electric dipole transition of the Eu3+ was found to be dominant, the prepared phosphors possessed high color purity (CP). The energy transfer mechanism and the lifetime values were also presented. The temperature‐dependent PL studies showed good thermal stability of the optimum sample. Various radiative transition properties were analyzed by the Judd–Ofelt theory. The photometric results reveal the color tuning ability and CP of the CLMV:xEu3+ phosphors. [ABSTRACT FROM AUTHOR]

The article explores the photoluminescence properties of UV, near-UV and blue excited BaWO 4 : Eu3+ red phosphors. The optical band gap narrowing is observed after adding Eu3+ ions. The excitation spectra exhibit a broad peak centred at 255 nm and several narrow peaks of Eu3+ ions at 362, 382, 395, 415 and 465 nm. The three peaks located at 255 (UV), 395 (near-UV) and 465 nm (blue) are the most intense and suitable for the excitation of the sample. The spectral profile of the emission spectra irradiated at 255, 395 and 465 nm are identical. The brightest emission is realized at 18 mol% doping of Eu3+ ions at 255 and 465 nm excitations. However, the optimum concentration is 16 mol% at 395 nm excitation. The phosphors emit highly pure red lights with color purity 98.192%, 97.794% and 98.693% for the optimised concentration under UV, near-UV and blue excitations of 255, 395 and 465 nm, respectively. The quantum efficiency of BaWO 4 : 16 mol% Eu3+ phosphor is calculated as∼48.234% at 395 nm excitation. The emission intensity parameters are calculated in view of the Judd-Ofelt theory. The spectroscopic parameters like radiative transition probability, radiative lifetime, branching ratio and stimulated emission cross-section are further evaluated from the three emission spectra recorded at 255, 395 and 465 nm excitations. The derived results advocate the use of synthesized material as a red phosphor in white-LED, laser and display devices. [ABSTRACT FROM AUTHOR]

A spectroscopic study of Eu3+, Tb3+ and Eu3+/Tb3+ ions-doped zinc sodium borotellurite (ZNB) glass synthesized by a melt-quenching method was performed via photoluminescence spectra and luminescence decay. The results of X-ray diffraction showed the amorphous materials of the prepared glass, and also indicated the difference in absorption spectra between glass samples doped by Eu3+ and Tb3+ ions. Three phonon energies of the ZNB host lattice were found around 932 cm−1, 1282 cm−1 , and 1892 cm−1 through the excitation spectra of Eu3+ and Tb3+ ions. The multiphonon relaxation rate (Wmp) was estimated for each phonon sideband and compared with previously reported results. Intensity parameters (Ωλ) were determined by the Judd–Ofelt theory and their values were used to evaluate the radiative transition of Eu3+ ions in ZNB glass, such as calculated lifetime (τcal), transition probability rate (A), effective line width (Δλeff), stimulated emission cross-section (σp), and branching ratio (βR). Eu3+/Tb3+ co-doped in ZNB glass exhibited multicolor emissions and the energy transfer process between Tb3+ and Eu3+ ions was confirmed based on the analysis of excitation spectra and decay time. [ABSTRACT FROM AUTHOR]

In this work, we evaluated the widths of the pionic and radiative transitions from the T c s ¯ 0 + (2900) to the D s 1 + (2460) in the D s 1 + (2460) molecular frame and the D s 1 + (2460) charmed-strange meson frame. Our estimations demonstrate that the transition widths in the D s 1 + (2460) molecular frame are much larger than those in the the D s 1 + (2460) charmed-strange meson frame. Specifically, the ratio of the widths of Γ (T c s ¯ 0 + (2900) → D s 1 + π 0) and Γ (T c s ¯ 0 + (2900) → D + (0) K 0 (+)) is estimated to be around 0.1 in the D s 1 + (2460) charmed-strange meson frame, whereas the lower limit of this ratio is 0.67 in the D s 1 + (2460) molecular frame. Thus, the aforementioned ratio could be employed as a tool for testing the nature of the D s 1 + (2460) . [ABSTRACT FROM AUTHOR]

The thermoluminescence (TL) kinetic parameters and radioluminescence results (RL) of RE3+ (RE = Pr, Sm, Tb, Ho, Er)-doped barium tantalate phosphors have been studied for different concentrations. The concentration quenching occurring at the RL intensity of Pr3+ after 1.5 mol% was associated with a cross-relaxation between 3P0 → 3H4 and 1D2 → 3H4, while the RL emissions of Tb3+ were observed corresponding to transitions of5D4 → 7FJ. The asymmetry ratio of RL is relatively high compared to the PL asymmetry ratio for Sm3+, which may be attributed to the RL mechanism leading to some decrease in the local symmetry of Sm3+ ions. The Ho3+ and Er3+ show the characteristic green and red emissions corresponding to radiative transitions. Also, the spectral properties of the phosphors have been discussed by comparing the RL results, the reported PL results of Pr3+, Sm3+, Ho3+, Er3+ , and the PL results of Tb3+ , which were examined in the study. After being irradiated by x-ray and short-wave UV light (254 nm), TL glow curves for Pr3+, Tb3+, and Er3+ doped phosphors were compared in the range of 50 °C and 400 °C at a heating rate of 2 °C s−1. TL glow peaks for Pr3+, Tb3+, and Er3+ formed at temperatures of 77 °C and 208 °C, 87 °C and 263 °C, and 158 °C and 267 C, respectively. The kinetic data were estimated by applying computerized glow curve deconvolution (CGCD) where TL glow curves of BaTa2O6:RE3+ (RE = Pr, Tb, Er) consist of 5, 6, and 7 estimated glow peaks with figure-of-merit values of 1.06, 1.60, and 1.09, respectively. [ABSTRACT FROM AUTHOR]

Bioprobe based on fluorescence is widely used in biological and medical research due to its high sensitivity and selectivity. Yet, its quantification in vivo is complicated and often compromised by the interaction between the fluorophore with the environmental factors, as well as the optical scattering and absorption by the tissue. A high florescence quantum yield and minimal interference by the environment are key requirements for designing an effective bioprobe, and the pre-requisitions severely limit the available options. We propose that a comprehensive evaluation of potential bioprobe can be achieved by simultaneously measuring both radiative and non-radiative transitions, the two fundamental and complementary pathways for the energy de-excitation. This approach will not only improve the accuracy of the quantification by catching the information from a broader spectrum of the energy, but also provide additional information of the probe environment that often impacts the balance between the two forms of the energy transition. This work first analyzes the underlying mechanism of the hypothesis. The practical feasibility is then tested by means of simultaneous measurements of photoacoustic signal for the non-radiative and fluorescence for the radiative energy processes, respectively. It is demonstrated that the systematic evaluation of the probe energy de-excitation results in an improved quantitative tracing of a bioprobe in complex environment. [ABSTRACT FROM AUTHOR]

The NaGdF4:Nd3+@Ni core@shell nanoparticles were synthesized and characterized. First, core@shell nanoparticles were synthesized using a solvothermal method to obtain the NaGdF4:Nd3+ core with hexagonal phase; subsequently, a chemical reduction was performed to stimulate the growth of the Ni shell with cubic phase. NaGdF4:Nd3+@Ni nanoparticles were characterized by transmission electron microscope, zeta potential, X-ray diffraction, scattered energy spectroscopy, UV-Vis, and photoluminescence emission spectra. The nanoparticles were round in shape, with mean sizes around 250 nm. The core@shell nanoparticles presented a homogenous composition and good stability. The photoluminescent emission of the nanoparticles was recorded at 1059 nm in the near-infrared spectral range; this band corresponds to the 4F3/2→4I11/2 radiative transitions of Nd3+ ions. The synthesized nanoparticles, being hydrophilic, have potential for use in different areas, one of them could be in anaerobic digestion. [ABSTRACT FROM AUTHOR]

Fiber laser sources operating near 2300 nm in the atmospheric transparency window are interesting for different applications, such as remote sensing, lidars, and others. The use of Tm-doped fiber lasers based on tellurite fibers is highly promising. We propose and theoretically study a highly efficient diode-pumped Tm-doped zinc-tellurite fiber laser operating at two cascade radiative transitions at 1960 nm and 2300 nm, with additional energy transfer between these laser waves due to the Raman interaction. We demonstrate numerically that a dramatic increase in the slope efficiency up to 57% for the laser wave at 2300 nm, exceeding the Stokes limit by 22% relative to the pump at 793 nm, can be obtained with optimized parameters thanks to Raman energy transfer from the laser wave at 1960 nm to the wave at 2300 nm. [ABSTRACT FROM AUTHOR]

Terahertz photoconductivity and charge carrier recombination dynamics at two-photon (ZnGeP2) and three-photon (4H-SiC) excitation were studied. Thermally annealed, high-energy electron-irradiated and Sc-doped ZnGeP2 crystals were tested. The terahertz charge carrier mobilities were extracted from both the differential terahertz transmission at a specified photoexcitation condition and the Drude–Smith fitting of the photoconductivity spectra. The determined terahertz charge carrier mobility values are ~453 cm2/V·s for 4H-SiC and ~37 cm2/V·s for ZnGeP2 crystals. The charge carrier lifetimes and the contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of bulk and surface Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that ZnGeP2 possesses short charge carrier lifetimes (a~0.01 ps−1, b~6 × 10−19 cm3·ps−1 and c~7 × 10−40 cm6·ps−1) compared with 4H-SiC (a~0.001 ps−1, b~3 × 10−18 cm3·ps−1 and c~2 × 10−36 cm6·ps−1), i.e., τ~100 ps and τ~1 ns at the limit of relatively low injection, when the contribution from Auger and interband radiative recombination is small. The thermal annealing of as-grown ZnGeP2 crystals and the electron irradiation reduced the charge carrier lifetime, while their doping with 0.01 mass % of Sc increased the charger carrier lifetime and reduced mobility. It was found that the dark terahertz complex conductivity of the measured crystals is not fitted by the Drude–Smith model with reasonable parameters, while their terahertz photoconductivity can be fitted with acceptable accuracy. [ABSTRACT FROM AUTHOR]

The fluorophores in the second near‐infrared (NIR‐II) biological window (1000 – 1700 nm) show great application prospects in the fields of biology and optical communications. However, both excellent radiative transition and nonradiative transition cannot be achieved simultaneously for the majority of traditional fluorophores. Herein, tunable nanoparticles formulated with aggregation‐induced emission (AIE) heater are developed rationally. The system can be implemented via the development of an ideal synergistic system that can not only produce photothermal from nonspecific triggers but also trigger carbon radical release. Once accumulating in tumors and subsequently being irradiated with 808 nm laser, the nanoparticles (NMB@NPs) encapsulated with NMDPA‐MT‐BBTD (NMB) are splitted due to the photothermal effect of NMB, leading to the decomposition of azo bonds in the nanoparticle matrix to generate carbon radical. Accompanied by second near‐infrared (NIR‐II) window emission from the NMB, fluorescence image‐guided thermodynamic therapy (TDT) and photothermal therapy (PTT) which significantly inhibited the growth of oral cancer and negligible systemic toxicity is achieved synergistically. Taken together, this AIE luminogens‐based synergistic photothermal‐thermodynamic strategy brings a new insight into the design of superior versatile fluorescent NPs for precise biomedical applications and holds great promise to enhance the therapeutic efficacy of cancer therapy. [ABSTRACT FROM AUTHOR]

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200–300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420–565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups. [ABSTRACT FROM AUTHOR]

Tellurite glasses doped with Tm3+, Ho3+ and Ce3+ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm3+/Ho3+ co-doping glass samples, which originated from the transitions of Ho3+:5I 7 →5I 8 and Tm3+:3F 4 →3H 6 , 3H 4 →3F 4 , 3F 2,3 → 3H 6 , respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm3+:3F 4 level to the Ho3+:5I 7 level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm3+/Ho3+ with 0.085 mol% Ho 2 O 3 and 1 mol% Tm 2 O 3 , the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO 2 , the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce3+ and Tm3+ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network. [ABSTRACT FROM AUTHOR]

As promising luminescent materials for organic light-emitting diodes (OLEDs), thermally activated delayed fluorescence materials are booming vigorously in recent years, but robust blue ones still remain challenging. Herein, we report three highly efficient blue and deep-blue delayed fluorescence materials comprised of a weak electron acceptor chromeno[3,2-c]carbazol-8(5H)-one with a rigid polycyclic structure and a weak electron donor spiro[acridine-9,9'-xanthene]. They hold distinguished merits of excellent photoluminescence quantum yields (99%), ultrahigh horizontal transition dipole ratios (93.6%), and fast radiative transition and reverse intersystem crossing, which furnish superb blue and deep-blue electroluminescence with Commission Internationale de I'Eclairage coordinates (CIEx,y) of (0.14, 0.18) and (0.14, 0.15) and record-beating external quantum efficiencies (ηexts) of 43.4% and 41.3%, respectively. Their efficiency roll-offs are successfully reduced by suppressing triplet-triplet and singlet-singlet annihilations. Moreover, high-performance deep-blue and green hyperfluorescence OLEDs are achieved by utilizing these materials as sensitizers for multi-resonance delayed fluorescence dopants, providing state-of-the-art ηexts of 32.5% (CIEx,y = 0.14, 0.10) and 37.6% (CIEx,y = 0.32, 0.64), respectively, as well as greatly advanced operational lifetimes. These splendid results can surely inspire the development of blue and deep-blue luminescent materials and devices. Thermally activated delayed fluorescence materials are important for the development of OLED materials but the development of robust blue emitting materials remains challenging. Here, the authors report three highly efficient blue and deepblue delayed fluorescence materials demonstrating excellent electroluminescence performance. [ABSTRACT FROM AUTHOR]

A series of Eu3+ and Eu3+/Gd3+ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd3+ to Eu3+ ions. The density of glasses increased with increasing of Gd3+ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu3+-Gd3+ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu3+: 5D 0 → 7F 2 transition. Less intense emissions centered at 577 nm (7F 0), 590 nm (7F 1), 651 nm (7F 3) and 700 nm (7F 4) are also observed from the radiative transitions of the excited state 5D 0 of Eu3+ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu3+ and 3.0 mol% Gd3+ co-doped glass under λ Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications. [ABSTRACT FROM AUTHOR]

Dysprosium-doped lead fluoro-borotellurophosphate glasses with the chemical composition of (25-x) H3BO3 + 10TeO2 + 25P2O5 + 10PbO + 08ZnF2 + 12NaF + 10Li2CO3 + xDy2O3 (x = 0.1, 0.25, 0.5, 1 & 1.5) were prepared by melt quenching technique. The structural and optical properties were studied to understand the behavior of Dy3+ ions with the local environment for photonic applications. The structural investigations were carried out through XRD, FTIR and SEM with EDS analysis. The absence of sharp peaks in the XRD pattern confirms the non-crystalline nature of the prepared glasses. The various functional groups of the composition were confirmed through FTIR. The surface morphology and the distribution of elements presented were observed through SEM with EDS. The optical behaviors were studied through UV–Vis-NIR, photoluminescence and chromaticity analysis. The JO intensity parameters Ωλ (λ = 2, 4, 6) were calculated, and the higher Ω2 value of BTPPZNL0.1D glasses indicates the asymmetry around Dy3+ ions. The radiative parameters like emission band position (λp), effective band width (Δλeff), radiative transition probability (A), stimulated emission cross section σ p E , and calculated and experimental branching ratios (βR) were determined from emission analysis. The higher value of stimulated emission cross section σ p E for 4F9/2 → 6H13/2 transition suggested that BTPPZNL1.5D glass is suitable for laser application. The evaluated color coordinates of prepared glasses represent the capacity of white light emission under UV excitation. [ABSTRACT FROM AUTHOR]

Dye lasers are commonly used in optical investigation because their solutions in organic solvents deliver tunable, coherent emissions. They exhibit intense fluorescence owing to some specific spectroscopic characteristics. One drawback of the laser dyes is that it shows excessive triplet-state losses (TSLs.) The lack of theoretical predictions of fluorescence rates, intersystem crossing (ISC), and phosphorescence in laser dyes prompted us to report on the predicted rates of radiative and nonradiative transitions of some laser dyes. Structural engineering by some substituents influencing the simulated rates of coumarin laser dye derivatives for an efficient operation was investigated. The NH2 functional group renders the coumarin 120 more fluorescents with reduced TLS than the other investigated materials. Tailoring new efficient laser dyes can be achieved guided by the calculated rates of emission and nonradiative processes. [ABSTRACT FROM AUTHOR]

The photoluminescence of Au(I) complexes is generally characterized by long radiative lifetimes owing to the large spin-orbital coupling constant of the Au(I) ion. Herein, we report three brightly emissive Au(I) coordination compounds, 1, 2a, and 2b, that reveal unexpectedly short emission lifetimes of 10–20 ns. Polymorphs 2a and 2b exclusively exhibit fluorescence, which is quite rare for Au(I) compounds, while compound 1 reveals fluorescence as the major radiative pathway, and a minor contribution of a microsecond-scale component. The fluorescent behaviour for 1–2 is rationalized by means of quantum chemical (TD)-DFT calculations, which reveal the following: (1) S0–S1 and S0–T1 transitions mainly exhibit an intraligand nature. (2) The calculated spin-orbital coupling (SOC) between the states is small, which is a consequence of overall small metal contribution to the frontier orbitals. (3) The T1 state features much lower energy than the S1 state (by ca. 7000 cm−1), which hinders the SOC between the states. Thus, the S1 state decays in the form of fluorescence, rather than couples with T1. In the specific case of complex 1, the potential energy surfaces for the S1 and T2 states intersect, while the vibrationally resolved S1–S0 and T2–S0 calculated radiative transitions show substantial overlap. Thus, the microsecond-scale component for complex 1 can stem from the coupling between the S1 and T2 states. [ABSTRACT FROM AUTHOR]

In this work, we present high-accuracy spectroscopic properties, such as line strengths, transition probabilities and oscillator strengths for allowed transitions among n D 3 / 2 , 5 / 2 , n ′ S 1 / 2 and n ′ P 1 / 2 , 3 / 2 (n = 4 , n ′ = 5 , 6) states of Rb-isoelectronic Tc (Tc VII), Ru (Ru VIII) and Rh (Rh IX) ions for their applications in the analysis of astrophysical phenomena occurring inside celestial bodies containing Tc, Ru and Rh ions. Due to the scarcity of computational data of atomic properties of these transitions, as well as considerable discrepancies within the literature about these ions, the precise determination of these properties is necessary. For this purpose, we have implemented relativistic many-body perturbation theory (RMBPT) for evaluation of the wave functions of the considered states. For better accuracy, we have accounted for electron interactions through random phase approximation, Brückner orbitals and structural radiations of wave functions in our RMBPT method for further precise evaluation of electric dipole amplitudes. Combining these values of the observed wavelengths, the above transition properties and radiative lifetimes, a number of excited states of Tc VII, Ru VIII and Rh IX ions have been calculated. For further validation of our work, we have compared our results with the data already available in the literature. [ABSTRACT FROM AUTHOR]

The results of experimental and theoretical studies on electron-impact excitation of the 6 s 6 p   P 1 °   3 → 6 s 2   S 0   1 (λ190.8 nm) and 6 s 7 s   S 0   1 → 6 s 6 p   P 1 °   3 (λ179.9 nm) intercombination transitions in the single-charged thallium ion are presented. The crossed-beams technique was used in combination with a spectroscopic method in the experiment. A distinct structure revealed in the cross-sections of both lines results from electron decay of atomic autoionizing states and radiative transitions from upper ionic levels. The dominant mechanism of the structure formation was the Coster–Kronig process. Relativistic distorted wave calculations were performed to obtain emission cross-sections for the above transitions. The absolute values of the cross-sections were found to be (0.25 ± 0.08) × 10−16 cm2 (λ190.8 nm) and (0.10 ± 0.04) × 10−16 cm2 (λ179.9 nm) at the electron energy of 100 eV. [ABSTRACT FROM AUTHOR]

The electrochemiluminescence (ECL) is generally emitted via radiative transition of singlet or triplet excited state (S1 or T1). Herein, an ECL mechanism with the transitions of both S1 and T1 of black phosphorus quantum dots (BPQDs) is found, and an arginine (Arg) modification strategy is proposed to passivate the surface oxidation defects of BPQDs, which could modulate the excited states for enhancing the ECL efficiency of BPQDs. The Arg modification leads to greater spatial overlap of highest and lowest occupied molecular orbitals, and spectral shift of radiative transitions, and improves the stability of anion radical of BPQDs. To verify the application of the proposed mechanism, it is used to construct a sensitive method for conveniently evaluating the inhibiting efficiency of cyclo-arginine-glycine-aspartic acid-d-tyrosine-lysine to cell surface integrin by using Arg containing peptide modified BPQDs as signal tag. The dual excited states mediated ECL emitters provide a paradigm for adjustable ECL generation and extend the application of ECL analysis. Electrochemiluminescence is emitted via the radiative transition of a singlet or triplet excited state. Here, the authors propose an arginine modification of black phosphorus quantum dots that exhibits enhanced emission based on dual excited states. [ABSTRACT FROM AUTHOR]

ZnO–P 2 O 5 glasses activated with Ag m n + clusters and Mn2+ ions were successfully synthetized by the melt-quenching method. X-ray diffraction patterns confirmed the glassy nature for doping concentrations up to 3.0 and 5.0 mol% of Ag+ and Mn2+ ions, respectively, whereas the Raman spectra in all cases displayed δ(P–O–P), ν s (P–O–P), ν s (PO 2) and ν as (PO 2) vibrational modes, typical of a phosphate glass network. The emission spectra under 345 nm (Ag m n + : S 0 → S 1 and Mn2+: 6A 1 (S) → 4T 1 (P) + 4E(D)), 385 nm (Ag m n + : S 0 → S 1) and 407 nm (Mn2+: 6A 1 (S) → 4A 1 (G) + 4E(G) and Ag m n + : S 0 → S 1) excitations, showed the broad band related to the superimposed Ag m n + cluster: S 1 → S 0 , T 2 → S 0 and T 1 → S 0 radiative transitions along with the Mn2+: 4T 1 (G) → 6A 1 (S) one. Under 385 nm excitation, the Mn2+ emission transition is attained by energy transfer from Ag m n + clusters. Such excitations lead to emission tonalities in the bluish white to cold white (345 and 385 nm) and cold white to reddish orange (407 nm) ranges, with correlated color temperature (CCT) values in the 10,095-5371 K (345 nm), 14,768-6862 K (385 nm) and 8592-1633 K (407 nm) ranges. Purplish pink emissions upon 345 nm excitation were obtained as well. The white color tonalities together with the color rendering index (CRI) and absolute quantum yield (QY, external) values up to 95 Ra and 35%, respectively, revealed promissory features for rare-earth-free white light emitting diode applications. The Ag m n + cluster: S 1 → S 0 emission fitting by the Burstein model suggested that the non-radiative energy transfer is mainly mediated by an electric dipole-dipole interaction. [ABSTRACT FROM AUTHOR]

Novel ternary fluoro-germano-tellurite (GTS) glasses doped with Er3+ ions with 0.5 mol% and 1.0 mol% were fabricated by a conventional melt and quenching method and investigated using methods of optical spectroscopy. The room-temperature absorption spectrum was recorded and analyzed to determine radiative transition rates, radiative lifetimes, and branching ratios of Er3+ luminescence. Decay curves of Er3+ luminesccence were recorded and analyzed. Temperature dependences of emission spectra and absorption spectra in the region from RT (room-temperature) up to 675 K were studied in detail. The contribution of competing radiative and nonradiative processes to the relaxation of luminescent levels of Er3+ was assessed. Absolute and relative sensitivity were established utilizing the comprehensive model based on thermally coupled 2H11/2/4S3/2 excited states of erbium. The high quantum efficiency of the first erbium-excited state and value of gain coefficient indicate that GTS:Er glass system can be considered as conceivable NIR (near infrared) laser material as well. [ABSTRACT FROM AUTHOR]

In the optical energy gap, visible and near-IR emission of halide phosphate glasses with a composition of 40P2O5-30ZnO-20LiCl-10BaF2 in mol% doped with 3.5 × 104 ppm Pr2O3, referred to as PZLBPr, were synthesized. The UV-VIS-NIR and spectroscopic properties of these glasses were also predicted. The current glasses had broadband emission photoluminescence covering a wavelength range of 1250 to 1700 nm when excited at 455 nm. These bands for near-infrared emission luminescence relate to the transitions 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3, 3F4 in the optical telecommunication window. The significant PL emission wideband was caused by the radiative transition from Pr3+: 1D2 to 1G4. At 445 nm excitation, these glasses exhibited emission bands that corresponded to blue/reddish orange spectral ranges in visible ranges. The prepared glass has a high lasing quality factor (Ω4/Ω6 = 0.9), high optical energy (4.72 eV), and quantum efficiency = 87.3% with FWHM = 156 nm of transition emission from the 1D2 → 1G4 level. As a result, broadband near infrared optical amplifiers can be fabricated from the prepared glasses. [ABSTRACT FROM AUTHOR]

The role is considered of all known potential sources of excitation of the 1D term of atomic oxygen in auroras and the value of their relative contributions to the emission intensity of 630.0-nm emission in the height interval of 100−300 km. The main attention is paid to the role of weak excitation sources of 1D terms, such as collisional interactions between the components of atmospheric gases N(2D) + O, N(2D) + O2,N(2P) + O2, and N+ + O2; direct electron impact O2 + e*; and the radiative transition O(1S) → O(1D) + hν557.7. It is shown that, despite the small partial contributions of these sources to the intensity of the 630.0-nm emission, their total contribution can be quite significant. The total efficiency of these sources varies from 66 to 6% with an increase in altitude from 100 to 300 km and is significant at altitudes below 200 km. It is shown that the influence of the decontamination process leads to the fact that, in the region of heights of ∼110−150 km, the set of reactions of collisional interactions of ionospheric plasma components N(2D) + O, N(2D) + O2,N(2P) + O2, and N+ + O2 becomes the second most efficient source contributing to the intensity of the 630.0-nm emission. [ABSTRACT FROM AUTHOR]

Recently, there have been significant interest in the wide potential of photoluminescence (PL) response of rare-earth doped perovskite oxide thin films in the field of optoelectronics. This work reports an effective method to modulate the PL properties of 0.8 mol%Sm3+-doped BaTiO 3 (BTO:Sm) thin films through static and dynamic strain. BTO:Sm films were epitaxially grown on LaAlO 3 (LAO), 0.7Pb(Mg 1/3 Nb 2/3)O 3 -0.3PbTiO 3 (PMN-PT), MgO, and Mica single-crystal substrates by pulsed laser deposition technique. Compared with the BTO:Sm/PMN-PT heterostructure which experiences minimal lattice mismatch effect, the PL intensity of BTO:Sm/LAO and BTO:Sm/MgO is enhanced by 818.1% and 1014.7%, respectively, due to static tensile/compressive strain (-0.429% and 0.461%) during the epitaxial growth process. In the flexible BTO:Sm/Mica heterostructure, dynamic strain is introduced through mechanical bending. Compared with the unbent state, the u-type and n-type bending modes increase the relative changes in PL intensity (Δ I / I) by 599.0% and 768.5%, respectively. Particularly, BTO:Sm/Mica also exhibits a remarkable optical transmittance exceeding 75% (500–2500 nm). The enhancement of PL intensity is closely related to the adjustment of lattice strain, which changes the crystal field strength of the BTO:Sm and the radiative transition probability. This work provides valuable insights for designing future optoelectronic devices and environmental monitoring equipment. It has the potential to advance photonics and sensor technologies, paving the way for innovation and exploration in these fields. • The enhancement of PL intensity in BTO:Sm thin films is achieved through static strain. • High-quality BTO:Sm thin film with high transmittance and low roughness is epitaxially grown on Mica substrates. • Dynamic tuning of the PL behavior in BTO:Sm thin film is achieved by applying bending induced dynamic strain. [ABSTRACT FROM AUTHOR]

Ram pressure stripping (RPS) is a process that removes the interstellar medium (ISM) quickly, playing a vital role in galaxy evolution. Previous RPS studies have treated the ISM as single-phase or lack the resolution and physical processes to properly capture the full multiphase ISM. To improve this simplification, we introduce an inflowing, hot intracluster medium (ICM) into a self-consistently modeled ISM in a local patch of star-forming galactic disks using the TIGRESS framework. Our simulations reveal that the workings of RPS are not only direct acceleration of the ISM by ICM ram pressure but also mixing-driven momentum transfer involving significant phase transition and radiative cooling. The hot ICM passes through the low-density channels of the porous, multiphase ISM; shreds the cool ISM; and creates mixing layers. The ICM momentum is transferred through the mixing layers while populating the intermediate-temperature gas and radiating thermal energy away. The mixed gas extends beyond galactic disks and forms stripped tails that cool back unless the ICM fluxes are large enough to prevent cooling until they escape the simulation domain. The mixing-driven momentum transfer predicts that the more ICM mixes in, the faster the ISM moves, resulting in the anticorrelation of outflow velocity and gas metallicity of the stripped ISM. The compression of the ISM disks due to the ICM ram pressure enhances star formation rates up to 50% compared to the model without ICM. With the ICM ram pressure higher than the disk anchoring pressure, star formation is quenched within ∼100 Myr. [ABSTRACT FROM AUTHOR]

We report a comparative study of coordination behaviour of 2-(2-aminophenyl)benzothiazole (NH2-pbt) and its phosphorus-containing derivative, α-aminophosphine oxide (PCNH-pbt), towards zinc halides. The corresponding coordination compounds [Zn(L)2Hal2] (L = PCNH-pbt, Hal = Cl, 1 and Hal = Br, 2) and [Zn(L')Hal2] (L' = NH2-pbt, Hal = Cl, 3 and Hal = Br, 4) were obtained as single phases. As evidenced by single-crystal X-ray diffraction analysis, L' ligand coordinates to Zn in a chelate manner via two N atoms. Despite a similar coordination mode in complexes 3 and 4, the spatial geometry of the ligand differs notably, which implies a relatively high flexibility of NH2-pbt. The L ligand exhibits another coordination mode, binding with Zn only via the oxygen of the P=O group. The differences in the structures of NH2-pbt, 3 and 4, and their counterparts, PCNH-pbt, 1 and 2, induce differences in their solid-state photoluminescence properties. The former group of the compounds exhibits conventional single-band emission, while the latter group reveals two bands. The minor band at 450 nm is ascribed to a radiative transition for the regular amine species, while the major band at 520–550 nm can be associated either with the proton-transferred imine species (ESIPT mechanism) or with a charge transfer state (TICT) with a different geometry. [ABSTRACT FROM AUTHOR]

The importance of the direct band structure of CdTe as a necessary condition for the creation of high-performance photoelectronic devices based on it is argued. The possibility of obtaining heterolayers (HLs) of cadmium tellurides by the method of isovalent substitution is shown. Prerequisites for manufacturing are determined and technological modes of isothermal annealing of α-CdSe and α-CdS base crystals are developed. For the first time, HLs with a little-used atypical hexagonal modification α-CdTe crystal lattice with highly stable properties are obtained by isovalent substitution. A technique is developed, and the basic parameters of the band structure and luminescence characteristics are studied by the method of γ-modulation of optical irradiation. The band gap Eg = 1.56 eV is established, and the parameters of the band structure are determined for the first time, namely, the subbands of the valence band split off due to the action of the crystal field Δcr ≈ 0.06 eV and the spin-orbit interaction Δso ≈ 0.38 eV. A high quantum efficiency η≈ 7-9 % of the dominant radiation in the edge region is established. It is determined by doping with isovalent impurities, which are the atoms of the base substrate. An important prerequisite for obtaining high intensity (compared to CdTe crystals with η~ 0.1-0.2 %) is the formation of a transition layer of the corresponding solid solution between the components of heterostructures, which significantly reduces the concentration of defects and the discrepancy between the crystalline and thermal parameters of the contacting materials. The obtained features of the crystal structure provide the conditions for the formation of effective luminescence, the basic mechanisms of which are interband radiative transitions and the dominant annihilation of excitons bound on isovalent impurities. [ABSTRACT FROM AUTHOR]

A high-luminescent, blue-light excitable europium(III) coordination complex, [Eu(µ2-OC2H5)(btfa)(NO3)(phen)]2phen (1) {btfa = benzoyl trifluoroacetone, phen = 1,10-phenantroline}, has been synthesized and investigated. The complex was characterized by infrared (IR) and photoluminescence (PL) spectroscopy. The PL emission spectra of powder samples registered in a range of 10.7–300 K exhibit characteristic metal-centered luminescence bands, assigned to internal radiative transitions of the Eu3+ ion, 5D1→7Fj and 5D0→7Fj (j = 0–4). The high-resolution spectrum of the transition 5D0→7F0 shows that it consists of two narrow components, separated by 0.96 meV, which indicates the presence in the matrix of two different sites of the Eu3+ ion. The splitting pattern of 5D0→7Fj (j = 0–4) transitions indicates that europium ions are located in a low-symmetry environment. The absolute quantum yield and the sensitization efficiency were determined to be 49.2% and 89.3%, respectively. The complex can be excited with low-cost lasers at around 405 nm and is attractive for potential applications in optoelectronics and biochemistry. [ABSTRACT FROM AUTHOR]

Results of experimental and theoretical investigations into the electron-impact excitation of the resonance 6 s 6 p 1 P 1 ° â†' 6 s 21 S 0 (132.2 nm), as well as the cascade 6 s 7 s 1 S 0 â†' 6 s 6 p 1 P 1 ° (309.2 nm) and 6 p 21 D 2 â†' 6 s 6 p 1 P 1 ° (150.8 nm) spectral transitions from the ground 6 s 21 S 0 level in the thallium ion, are presented. Crossed beams of electrons and Tl+ ions in combination with a spectroscopic method were used in the experiment. Measured cross sections have a distinct resonance structure arising mainly from the electron decay of atomic 5 d 96 s 26 p 2, 5 d 106 s 7 s (1 S) np (n â©ľ 7), 5 d 106 s 6 d (1 D) np (n â©ľ 6), 5 d 106 s 6 d (1 D) nd (n â©ľ 6) and ionic 5 d 96 s 2 np, 5 d 96 s 2 nd, 5 d 96 snp (n â©ľ 6) autoionizing levels, as well as radiative transitions from the higher 6 s 7 s 1 S 0, 6 s 6 d 1 D 2, and 6 p 21 D 2, 1 S 0 ionic levels. Relativistic distorted wave (RDW) calculations are performed to obtain the effective cross sections for the above transitions. The absolute values of the cross sections are found to be 1.39 Ă— 10âˆ'16 cm2 at 300 eV for the λ 132.2 nm resonance line, and 0.11 Ă— 10âˆ'16 cm2 and 0.56 Ă— 10âˆ'16 cm2 at 100 eV for the λ 309.2 nm and λ 150.8 nm lines, respectively. The contribution of the cascade transitions being studied to the effective cross section of the λ 132.2 nm resonance line at the energy of 100 eV is about 30%. A calculation using the semi-empirical Van Regemorter formula is also performed to obtain the effective cross section of the resonance λ 132.2 nm line. The absolute value of the cross section at 300 eV is found to be nearly the same as that given by the RDW calculation. [ABSTRACT FROM AUTHOR]

Antimony-lead-oxyfluoroborate (SbPbOFB) glasses doped with various concentrations of Eu3+ ions were prepared by employing melt quenching and their luminescence activity was characterized using different spectroscopic methods such as optical absorption, photoluminescence (PL) excitation, PL emission, and PL decay. The Raman spectrum was recorded for an un-doped SbPbOFB glass to identify various functional groups present. The optical absorption spectra recorded for Eu3+ ion-doped SbPbOFB glasses showed five bands corresponding to 7F0→5L6, 7F0→5D2, 7F1→5D1, 7F0→7F6 and 7F1→7F6 transitions. The PL spectra measured under 394-nm excitation wavelength show five peaks corresponding to 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transitions at 578, 592, 613, 652 and 701 nm, respectively. Among them, that pertaining to the 5D0→7F2 transition appeared at 613 nm in the visible red region showing relatively high intensity. The Judd-Ofelt (J-O) parameters evaluated from the absorption spectral data are correlated with the prominent emission spectral features such as 5D0→7F1 (592 nm), 5D0→7F2 (613 nm) and 5D0→7F4 (701 nm) to estimate radiative properties such as transition probabilities (AR), branching ratios (βR) and emission cross sections (σ se). Quantum efficiency (η%) of the prepared glasses was estimated by correlating the radiative lifetimes with the experimental lifetimes measured from the PL decay spectral features. The PL emission spectral features are used to estimate the CIE color coordinates (x, y) of the studied glasses. The measured βR, σ se, η%, and the CIE coordinates estimated for the studied glasses revealed their suitability for visible red light-emitting device applications. [ABSTRACT FROM AUTHOR]

We briefly discuss the history of pumping schemes for the common 22-GHz maser transition in o-H2O, and note that radiative mechanisms have been considered in the past, as well as the better known collisional pumping mechanisms associated with shock waves. Substantial IR irradiation is indeed destructive to inversion at 22-GHz under a wide range of physical conditions. We identify a small number of transitions, including 22 GHz, that can be pumped by both collisional and radiative schemes, and, through radiative transfer modelling over a grid of values in kinetic temperature, number density, and dust temperature, identify loci in density-kinetic temperature space where these schemes lead to strong inversions. The radiative pumping scheme generally operates at higher dust temperature, and lower kinetic temperature, than the collisional scheme. We identify a small network of transitions that form a radiative pumping scheme for the 22-GHz maser, involving radiative transitions of wavelength approximately 6  |$\mu$| m. This network is capable of supplying more than 50 per cent of the 22-GHz inversion under typical radiative pumping conditions, and it is consistent with the need for high dust and low kinetic temperatures determined from the modelling. We identify a probable case of radiative pumping in a massive star-forming region from the observation of a positive correlation between the flux densities of 22-GHz H2O masers and 6.7-GHz methanol masers. We discuss possibilities for finding radiatively pumped H2O maser lines in other source types. [ABSTRACT FROM AUTHOR]

In this study, a series of well-crystallized Yb3+/Er3+/Tm3+-tridoped Y2O3-ZnO ceramic nano-phosphors were prepared using sol–gel synthesis, and the phosphor structures were studied using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The phosphors were well crystallized and exhibited a sharp-edged angular crystal structure and mesoporous structure consisting of 270 nm nano-particles. All phosphors generated blue, green, and red emission bands attributed to Tm: 1G4→3H6, Er: 2H11/2 (4S3/2)→4I15/2, and Er: 4F9/2→4I15/2 radiative transitions, respectively. Increasing in luminescent centers, weakening of lattice symmetry, and releasing of dormant rare earth ions can enhance all emissions. Er3+ can obtain energy from Tm3+ to enhance green and red emission. These colors can be tuned by optimizing the doping concentrations of the Er3+ ion. The color coordinates were adjusted by tuning both the Er3+ concentration and excitation laser pump power to shift the color coordinates and correlated color temperature. The findings of this study will broaden the potential practical applications of phosphors. [ABSTRACT FROM AUTHOR]

The population of the 2 s -level of hydrogen formed in the early Universe is studied within a standard and a non-standard quasi-molecular mechanism of recombination. We demonstrate that, if hydrogen molecular ion |$H_2^+$| temporarily formed during a collision directly dissociates into a hydrogen atom and a proton, both mechanisms of recombination lead to the same probabilities of population. These probabilities differ significantly, however, when attractive quasi-molecular channels are uninvolved and only repulsive channels remain in the treatment. The probabilities of the direct and indirect radiative transitions into the 2 s -level of hydrogen are evaluated. The dominant process in the population of 2 s -level of hydrogen is the direct free–bound radiative transition. [ABSTRACT FROM AUTHOR]

The Si2C and SiC2 both are considered to play key role in the formation of the SiC dust grains in the atmosphere of the carbon-rich stars. The molecule of our interest Si2C has been detected in the envelope of the red supergiant star IRC+10216 first time. It is an asymmetric top molecule having electric dipole moment of 1 Debye along the b-axis of inertia. Because of zero nuclear spin of both the Carbon and Silicon atoms, it has only paratransitions. Using the given spectroscopic data (rotational and centrifugal distortion constants and electric dipole moment), for the para-Si2C, we have calculated energies of 200 lower rotational levels (having energy up to 217.8 cm-1) and the Einstein A and B coefficients for 867 radiative transitions between the levels. We have solved a set of 200 statistical equilibrium equations coupled with 867 equations of radiative transfer (Sobolev analysis), where the collisional rate coefficients are taken from a scaling law. Out of 867 radiative transitions, 13 transitions have been found showing weak MASER action, and 19 transitions showing anomalous absorption. One transition 808-717 is found to show both the MASER action as well as the anomalous absorption. These transitions in addition to the observed transitions may play important role in the identification of Si2C in the cosmic objects. [ABSTRACT FROM AUTHOR]

The amplitude T for 'free-free' processes such as bremsstrahlung or photoabsorption by an electron in the continuum in the presence of an external field, is usually written as the matrix element of the radiation operator taken between two continuum states. However, unlike the case when at least one of the states is bound, as in radiative transitions, electron capture or the photo-effect, this expression contains unphysical term, proportional to a delta function, and is not really the physical amplitude T p h y s . We first give an a priori definition of T p h y s in terms of the scattering parts of the continuum functions, which does not have this delta function term and has an obvious interpretation in terms of time-ordered diagrams. We then show that when the formal amplitude T is modified by a long-distance cutoff, the modified form T α approaches T p h y s as the cutoff is removed. The modified form may be used as the basis for calculation and approximations without the need to introduce further cutoffs at a later stage. [ABSTRACT FROM AUTHOR]

Solution-processed polymer light emitting devices (PLEDs) using high-quality thermally activated delayed fluorescence (TADF) polymers as the emitting layers are attractive, however, high-efficiency white-light TADF polymers are very rare because of the complicated radiative transition channels. In this study, a series of hyperbranched TADF conjugated polymers were designed and synthesized which adopted the linear D-A-type TADF emitter of 1,8-naphthalimide-acridine as red chromophores, conjugated poly(fluorene-carbazole) as the blue backbone and triphenylamine as the hyperbranched cores. By adjusting the appropriate feed ratios of monomers, energy transfer process from the blue backbone to the red chromophores could be regulated and HR0.8 film had the highest photoluminescent quantum yield of 24 %. Consequently, its doped electroluminescent device showed the cold-white emission with the CIE color coordinates of (0.35, 0.23) and the maximum EQE of 6.82 %. By simply raising the concentration of the red chromophore in the polymers, the rapid reverse intersystem crossing (RISC) process and the enlarged energy gap between S 1 and T 1 were achievable. [Display omitted] • A series of hyperbranched conjugated polymers with excellent TADF character were designed and synthesized. • By raising the concentration of red chromophores, the reverse intersystem crossing rates was improved. • All polymers had flat and smooth film morphologies. • HR0.8 devices showed the best white light with a CIE coordinate of (0.35, 0.23) and the maximum EQE of 6.82%. [ABSTRACT FROM AUTHOR]

Based on the local surface plasmon resonance effect of Ag nanolayer, the luminescence enhancement in the visible light range of multilayer thin film has been investigated combined with metal/spacer molecule/photoluminescence material structure. The luminescence enhancement effect of multilayer thin films can be improved by adjusting the spin-coating number of Ag nanolayer and SiO 2 spacer in the multilayer structure. At the same time, the mechanism of enhanced luminescence has been analyzed according to the change in fluorescence lifetime. The effect of the coupling between Ag nanolayer and luminescence layer on the radiative transition rate and fluorescence quantum yield have been discussed. The up-conversion luminescence intensity of the noble metal-modified multilayer thin film can be further improved by combining the multilayer structure with sensitized layer. • The emission intensity of thin films are improved via the LSPR effect of Ag nanolayer. • On the basis of Ag@Tm/Yb structure, SiO 2 spacer layer is introduced to further enhance the upconversion luminescence. • The mechanisms of luminescence enhancement in the multilayer thin films are analyzed. • More than 20 times emission enhancement is achieved in the Ag@SiO 2 @Tm/Yb@Yb multilayer thin films. [ABSTRACT FROM AUTHOR]