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Thermoluminescent behavior of UV and γ rays irradiated Eu2+ and Er3+doped silicate phosphors
摘要： This paper reports the structural, morphological and thermoluminescent studies of Eu2+ and Er3+ ions activated ASiO3 (A= Ca, Ba, Sr) phosphors synthesized via conventional solid state reaction method. The impurity ions concentration of both Eu2+ and Er3+ ions varies from 0 mol% to 1 mol%. The study of crystallographic traits of the synthesized phosphors is done by Powder X-Ray Diffraction (PXRD) analysis. The crystalline nature, phase purity and appreciable homogeneity of the synthesized phosphors were confirmed by this study. The distinct morphological and topographical features were studied through Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The thermoluminescent (TL) behavior of ultraviolet (UV) irradiated and gamma irradiated ASiO3:Eu2+, Er3+ (A= Ca, Ba, Sr) phosphors were studied here and the various kinetic parameters were estimated by Computerised glow curve deconvolution (CGCD) technique and peak shape method. The UV and gamma irradiated phosphors exhibit second order kinetics. The high values of activation energy (~ 3 eV) confirm the trapping of electrons in deep trap centers. The incorporation of doping ions into the host lattice causes non-valence substitutions at the substitutional sites. This increases the number of defects and vacancies in the phosphors and more trap centers were generated. The increased TL intensity and high temperature glow peaks confirm the same. The synthesized phosphors show enhanced TL characteristics, efficient trapping mechanism and low fading effects. These characteristics confirm the suitability of the synthesized phosphors for TL mapping and sensing applications.
关键词： Alkaline earth silicates,Thermoluminscence,Activation energy,Trap depth,Order of kinetics.
更新于2025-09-23 15:23:52
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Synthesis and Optical Properties of the Eu2+-Doped Alkaline-Earth Metal Hydride Chlorides AE7H12Cl2 (AE = Ca and Sr)
摘要： In our study of the optical properties of Eu2+-doped alkaline-earth metal hydride chlorides AE7H12Cl2 (AE = Ca and Sr) we observe yellow (AE = Sr) and orange-red (AE = Ca) emission. Compared to the emission energies of Eu2+ - doped fluorides, chlorides and mixed fluoride chlorides, this corresponds to a wide redshift of the Eu2+ 4f65d1–4f7 emission. We explain this observation with the strong polarizability of the hydride anion and therefore its strong nephelauxetic effect, which shifts the 5d barycenter to lower energy. Furthermore, the redshift is even significant compared to other known hydride chlorides and hydride oxide chlorides, which is probably caused by the relatively short AE2+/Eu2+?H? distances, or it might also be caused by impurity-trapped exciton states. We have also investigated the temperature dependence of the photoluminescence lifetimes and the thermal stability. Even though the compounds are probably not ideal for phosphor application due to their low stability against air and moisture, our study underlines the large influence of the highly polarizable hydride anion on the optical properties of divalent europium and shows that Eu2+ could be used as a probe in mixed anionic system to determine the hydride content.
关键词： Hydride Chlorides,Eu2+ Luminescence,Alkaline-Earth Metals
更新于2025-09-23 15:22:29
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Comparison between 403 nm and 497 nm repumping schemes for strontium magneto-optical traps
摘要： The theoretical description of the external degrees of freedom of atoms trapped inside a magneto-optical trap (MOT) often relies on the decoupling of the evolution of the internal and external degrees of freedom. That is possible thanks to much shorter timescales typically associated with the first ones. The electronic structure of alkaline-earth atoms, on the other hand, presents ultra-narrow transitions and metastable states that makes such an approximation invalid in the general case. In this article, we report on a model based on open Bloch equations for the evolution of the number of atoms in a magneto-optical trap. With this model we investigate the loading of the strontium blue magneto-optical trap under different repumping schemes, either directly from a Zeeman slower, or from an atomic reservoir made of atoms in a metastable state trapped in the magnetic quadrupolar field. The fluorescence observed on the strong 461 nm transition is recorded and quantitatively compared with the results from our simulations. The comparison between experimental results and calculations within our model allowed to identify the existence of the decay paths between the upper level of the repumping transition and the dark strontium metastable states, which could not be explained by electric dipole transition rates calculated in the literature. Moreover, our analysis pinpoints the role of the atomic movement in limiting the efficiency of the atomic repumping of the Sr metastable states.
关键词： cold atoms,magneto-optical trap,repumping schemes,inhomogeneous Bloch equations,alkaline-earth atoms
更新于2025-09-23 15:22:29
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A Density Functional Theory Study on Nonlinear Optical Properties of Double Cage Excess Electron Compounds: Theoretically Design M[Cu(Ag)@(NH <sub/>3</sub> ) <sub/><i>n</i> </sub> ](M?=?Be, Mg and Ca; <i>n</i> ?=?1-3)
摘要： In this work, we investigated the nonlinear optical (NLO) properties of excess electron electride molecules of M[Cu(Ag)@(NH3)n] (M = Be, Mg and Ca; n = 1–3) using density functional theory (DFT). This electride molecules consist of an alkaline-earth (Be, Mg and Ca) together with transition metal (Cu and Ag) doped in NH3 cluster. The natural population analysis of charge and their highest occupied molecular orbital suggests that the M[Cu(Ag)@(NH3)n] compound has excess electron like alkaline-earth metal form double cage electrides molecules, which exhibit a large static ?rst hyperpolarizability (βe0) and one of which owns a peak value of βe0 216,938 (a.u.) for Be[Ag@(NH3)2] and vibrational harmonic ?rst hyperpolarizability.
关键词： NLO,transition metal,alkaline-earth,DFT,double cage excess electron compounds
更新于2025-09-23 15:21:21
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C-doping into h-BN at low annealing temperature by alkaline earth metal borate for photoredox activity
摘要： BCN (boron carbon nitride) nanosheets are promising photocatalyst materials for solar fuel production by visible light-driven water splitting and CO2 reduction due to their tunable band gap and unique properties. C-doping into h-BN by thermal annealing makes possible the preparation of BCN nanosheets with photocatalytic activity under visible light irradiation, but it generally requires a very high temperature (>1250 °C) from the thermodynamic viewpoint. Here, we report a new method to prepare BCN nanosheets with visible light-photocatalytic activity at lower annealing temperature (1000 °C) than equilibrium by adding alkaline earth metal compounds. BCN nanosheets formed in borate melt show a clear layered structure, tunable bandgap and photocatalytic activity for water splitting and CO2 reduction under visible light illumination. This provides a direction for doping other elements into h-BN at low annealing temperature by alkaline earth metal borates.
关键词： h-BN,low annealing temperature,BCN nanosheets,water splitting,CO2 reduction,C-doping,photoredox activity,alkaline earth metal borate
更新于2025-09-19 17:15:36
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Alkaline-Earth Bis(trifluoromethanesulfonimide) Additives for Efficient and Stable Perovskite Solar Cells
摘要： Environmental instability of Spiro-OMeTAD-based hole transport layer (HTL) caused due to rapid aggregation and hydration of its additive, Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI), gives rise to an accelerated degradation of the resulting perovskite solar cells (PSCs). Herein, we show that replacing the Li-TFSI with the more hydrophobic alkaline-earth bis(trifluoromethanesulfonyl)imide additives, namely Mg-TFSI2 and Ca-TFSI2, can effectively stabilize the coordination complexes between the TFSI-salts and 4-tert-Butylpyridine, which in turn results in retarded additive aggregation and hydration, enabling enhanced moisture-resistance of the subsequent HTLs. Moreover, by manipulating this substitution method, we achieved high-quality HTLs with increased hole mobility, better-formed interface with the adjacent perovskite, allowing improved hole extraction process. Incorporating these HTLs into photovoltaic devices, we obtained a substantial performance improvement, with the champion PSC yielded a power conversion efficiency of over 20%. In addition, un-encapsulated devices stabilized by the alkaline-earth bis(trifluoromethanesulfonyl)imide additive maintained 83% its initial efficiency for 193 days after aging in ambient air (RH% = 55-70%).
关键词： Perovskite solar cells,4-tert-Butylpyridine,environmental stability,alkaline-earth bis(trifluoromethanesulfonimide),hole transport layer,charge transfer
更新于2025-09-12 10:27:22
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Towards a rational design of laser-coolable molecules: insights from equation-of-motion coupled-cluster calculations
摘要： Access to cold molecules is critical for quantum information science, design of new sensors, ultracold chemistry, and search of new phenomena. These applications depend on the ability to laser-cool molecules. Rigorous theory and qualitative models can play a central role in narrowing down the vast pool of potential candidates amenable to laser cooling. We report a systematic study of structural and optical properties of alkaline earth metal derivatives in the context of their applicability in laser cooling using equation-of-motion coupled-cluster methods. To rationalize and generalize the results from high-level electronic structure calculations, we develop an effective Hamiltonian model. The model explains the observed trends and suggests new principles for the design of laser-coolable molecules.
关键词： laser cooling,alkaline earth metal derivatives,effective Hamiltonian model,quantum information science,equation-of-motion coupled-cluster methods,ultracold chemistry
更新于2025-09-11 14:15:04
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Effect of Li co-doping with Er on up-conversion luminescence property and its temperature dependence of NaY(WO4)2
摘要： NaY(WO4)2 phosphors with different Er3+ doping and Er3+/Li+ co-doping concentrations were prepared via high temperature solid state reaction. X-ray diffraction measurement demonstrated the presence of tetragonal-phase NaY(WO4)2, and no impurity phase was found in Er3+/Li+ co-doped samples. Well-crystallized NaY(WO4)2 phosphors showed a fine morphology with particle sizes of 1–6 μm determined by scanning electron microscope. Under excitation at 980 nm, the origins of three emission peaks located at 527 nm (green emission 1), 549 nm (green emission 2) and 665 nm (red emission), respectively, were identified. By introducing Li+, the up-converted (UC) emission intensity was enhanced by 0.5 times and 2 times in green and red emission region, respectively. The enhanced luminescence was attributed to the distortion of the local symmetry around Er3+ due to Li+ incorporation in the lattices. The 2H11/2 → 4I15/2 (green emission 1) and 4S3/2 → 4I15/2 (green emission 2) transitions of the Er3+ ion presented a temperature dependent behavior from 300 to 30 K and were proposed for temperature sensing (optical thermometry) by using the fluorescence intensity ratio (FIR) method. The FIR data obtained by experiment was well fitted with a theoretical function. A higher maximum value of sensitivity (0.0061 K-1) was obtained in 5% Er3+, 0% Li+ doped sample at 300 K. However, due to the distortion of local crystal field around Er3+ ions caused by the introduction of Li+, the sensitivity value of 5% Er3+ and 1% Li+ co-doped sample was higher than that of Li+ free sample below 270 K, which indicated that appropriate Li+ co-doping could optimize the temperature sensing behaviors of Er3+ doped NaY(WO4)2 phosphors.
关键词： Upconversion photoluminescence,Li+ co-doping,Alkaline earth oxides,Temperature sensing
更新于2025-09-10 09:29:36
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Ytterbium, You are Cool Enough to Go under the Quantum Gas Microscope!
摘要： Researchers at Kyoto University have developed a novel technique for imaging alkaline-earth atoms using a quantum gas microscope. Ytterbium (Yb) plays an important role in the Atomic, Molecular, and Optical (AMO) physics community because its optical properties are well suited for various applications. The Yb ion is popular as a doping material for fiber lasers and amplifiers. Narrow optical transitions in Yb atoms have been used in optical lattice clock experiments to attain the best performance for optical frequency standards. Now, Shibata et al. claim that a quantum gas of Yb atoms can be studied using a microscope to solve the mystery of strongly correlated gases.
关键词： strongly correlated gases,alkaline-earth atoms,quantum gas microscope,optical lattice,Ytterbium
更新于2025-09-04 15:30:14