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Crystal growth and optical characterization of an organic single crystal for frequency conversion applications
摘要： Organic nonlinear optical 2-methylquinolinium L-malate single crystals have been grown by slow evaporation solution growth technique from a mixture of 2-methylqiunoline and L-malic acid in ethanol solution at ambient temperature. Single crystal X-ray diffraction analysis reveals that grown crystal in monoclinic system with non-centrosymmetric space group P21 and the lattice parameters are a = 7.35 ?, b = 26.51 ?, c =10.83 ?, α = γ = 90o, β = 102.95o and V = 2057.4 ?3. UV-vis spectrum indicates that the crystal is transparent (75%) in the entire visible region with a cut-off wavelength of 437 nm and optical energy band gap Eg is found to be 2.71 eV. Microhardness measurement reveals the mechanical strength of the grown crystal. The photoluminescence spectrum shows the blue emission of the crystal. Laser damage threshold studies was carried out to ascertain the suitability of grown crystal for laser applications.The relative second harmonic generation efficiency of 2-methlquinolinium L-malate crystal was found to be two times greater than that of KDP.
关键词： Photoluminescence,Optical band gap,SHG studies,Laser damage threshold,Crystal growth
更新于2025-09-10 09:29:36
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On the influence of dilute charged impurity and perpendicular electric field on the electronic phase of phosphorene: Band gap engineering
摘要： Tuning the band gap plays an important role for applicability of 2D materials in the semiconductor industry. The present paper is a theoretical study on the band gap engineering using the electronic density of states (DOS) of phosphorene in the presence of dilute charged impurity and of a perpendicular electric field. The electronic DOS is numerically calculated using a combination of the continuum model Hamiltonian and the Green’s function approach. Our findings show that the band gap of phosphorene in the absence and presence of the perpendicular electric field decreases with increasing impurity concentration and/or impurity scattering potential. Further, we found that in the presence of opposite perpendicular electric fields, the electronic DOS of disordered phosphorene shows different changing behaviors stemming from the Stark effect: in the positive case the band gap increases with increasing electric-field strength; whereas in the negative case the band gap disappears. The latter, in turn, leads to the semiconductor-to-semimetal and semiconductor-to-metal phase transition for the case of strong impurity concentrations and strong impurity scattering potentials, respectively. The results can serve as a base for future applications in logic electronic devices.
关键词： Stark effect,perpendicular electric field,semiconductor-to-semimetal transition,phosphorene,band gap engineering,electronic density of states,semiconductor-to-metal transition,dilute charged impurity
更新于2025-09-10 09:29:36
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Tailoring the Structural and Optical Parameters of Eu3+:CeO2-SiO2 Nanopowder Via Thermal Treatment
摘要： Nanocrystalline Eu3+:CeO2-SiO2 powder samples were prepared by sol-gel technique. This technique is suitable for large-scale production and it is also a cost effective process. The prepared samples were annealed at different temperatures which were characterized by many complementary techniques. The formation of cubic fluorite structure of CeO2 nanocrystal with a uniform distribution was confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The average nanocrystalline size has been calculated as 3, 7 and 15 nm using Debye-Scherrer formula for different annealed samples. The calculated nanocrystalline sizes were compared with W-H plot and TEM histograms. It was investigated that FWHM of diffraction peaks decreases with increase in temperature results in increase nanocrystalline size. The FTIR spectroscopy provides the valuable information and identification of different chemical group/bonds present in the prepared samples. It is found that if we fixed the dopant concentration, then particle size, morphology and band gap energy of prepared nanopowder can be tailored by applying the annealing conditions. Comparative studies of absorption spectra and corresponding band gap energies have been done and a red shift has been observed in absorption spectra with thermal treatment. The shift of the optical absorption edge of prepared nanopowder towards lower energies increases its utilization in the visible region specially photocatalytic activity.
关键词： Thermal annealing,Absorption spectra,Structural properties,Nanopowder,Band gap energy
更新于2025-09-10 09:29:36
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Fabrication of Gd-La codoped TiO2 composite via a liquid phase plasma method and its application as visible-light photocatalysts
摘要： TiO2 was doped simultaneously with Gd and La using a liquid phase plasma (LPP) reaction to produce a photocatalyst with excellent photoactivity in the visible light region. Gadolinium chloride hexahydrate and lanthanum chloride heptahydrate precursors were used to dope the TiO2 powder with polycrystalline Gd2O3 and La2O3 particles. The doping of TiO2 with rare earth elements using LPP reaction decreased the band gap; the band gap of Gd-La codoped TiO2 photocatalysts (GLTP) was the lowest. The photodegradation efficiency of the TiO2 photocatalysts doped with either Gd or La was superior that of bare TiO2 but the photodegradation efficiency of GLTP was highest in both ultraviolet and visible light sources. Acetaminophen (Acetyl-para-aminophen, APAP) was ultimately decomposed to CO2 and H2O via intermediates, such as p-nitrophenol, hydroquinone and hydroxylhydroquinone, by hydroxyl radicals (HO?) formed on the surface of GLTP.
关键词： Liquid phase plasma,Gd-La codoped TiO2 photocatalysts,Band gap energy,Acetaminophen,Photocatalytic activity
更新于2025-09-10 09:29:36
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The electronic and optical properties of armchair germanene nanoribbons
摘要： The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n=3P, n=3P+1, n=3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG (3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.
关键词： electronic and optical properties,silicene,band gap size,graphene,germanene nanoribbons
更新于2025-09-10 09:29:36
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Pressure-Induced Broadband Emission of 2D Organic-Inorganic Hybrid Perovskite (C <sub/>6</sub> H <sub/>5</sub> C <sub/>2</sub> H <sub/>4</sub> NH <sub/>3</sub> ) <sub/>2</sub> PbBr <sub/>4</sub>
摘要： 2D Ruddlesden–Popper halide perovskites, which incorporate hydrophobic organic interlayers to considerably improve environmental stability and optical properties diversity, have attracted substantial research attention for optoelectronic applications. The burgeoning broad emission arising from exciton self-trapping of 2D perovskites shows a strong dependence on a deformable structure. Here, the pressure-induced broadband emission of layered (001) Pb-Br perovskite with a large Stokes shift in the visible region is observed by finely improving lattice distortion to increase exciton–phonon coupling under hydrostatic pressure. Band gap narrows ≈0.5 eV under modest pressure, mainly due to the large compressibility of the orientational organic layer, confirming that the bulky organic cations notably influence the structure and, in turn, the various properties of materials. Sequential amorphization of the organic and inorganic layer is confirmed by high pressure Raman and X-ray diffraction measurements, suggesting the particularity of layered crystal structures. The mechanism constructed here offers a new route for tuning the optical properties of 2D perovskites.
关键词： broadband emission,band-gap narrowing,pressure,perovskites,amorphization
更新于2025-09-10 09:29:36
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Structure characterization and photoluminescence of sol-gel synthesized Ag-Dy-codoped silica phosphor
摘要： Bulk samples of single Ag-, Dy-doped and Ag-Dy-codoped silica matrices were synthesized using the sol-gel processing. These matrices were characterized using X-ray di?ractometry, ultraviolet-visible-near infrared (UV-VIS-NIR), Fourier transform infrared, photoluminescence (PL) excitation and emission spectroscopic techniques. High resolution transmission electron microscope con?rmed the presence of ?ne spherical Ag nanoparticles (NPs), whose average size is approximately 10–15 nm, in the Ag-doped and Ag-Dy-codoped silica matrices. UV-VIS-NIR spectra revealed absorption peaks due to Dy3+ active centers in addition to the surface plasmon resonance bands of Ag NPs centered at 410 and 452 nm in these matrices, respectively. UV-excited PL of the materials was studied and compared. Near-white light emission, which was assessed by the calculated CIE chromaticity coordinates, could be observed under UV excitation at 365 nm in the Ag-Dy-codoped silica matrix. This white light was realized by appropriate combination of prominent yellow and blue emissions. Electron spin resonance spectra revealed paramagnetic spin states for Ag which can be attributed to the quantum size e?ect of very ?ne Ag NPs dispersed in the silica network. The obtained results indicate that the Ag-Dy-codoped silica phosphor could be a promising candidate for application as white light emitting phosphor for UV LED chips.
关键词： Sol-gel,TEM,Surface plasmon resonance,Phosphors,White LED,Optical band gap
更新于2025-09-10 09:29:36
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First principle calculations of electronic, band structural, and optical properties of BixSr1-xTiO3 perovskite
摘要： Based on the first-principles plane-wave ultrasoft pseudopotential method, we set up models of perovskite-type oxides BixSr1-xTiO3 (x=0, 0.25, 0.5, 0.625, 1), and the geomertry optimization, the electronic and band structure were studied. The calculation results show that the binding energy decreases in BixSr1-xTiO3 after Sr2+ replaced by Bi3+. The calculations of the band structure show that BixBa1-xTiO3 are direct band gap semiconductors. The partial substitution of Bi3+ ions can increase the band gap and the absorption spectra ranges shift blue, and the values of band gaps are in the order of Bi0.625Sr0.375TiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3>BiTiO3, and the absorption spectrum becomes wider in the order of Bi0.625Sr0.375TiO3>BiTiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3. Based on the density of states, the top of the valence band is hybridized by O-2p and Sr-5s and the bottom of the conduction band state is mainly constituted by the Ti-3d state and Bi-6p. The regulation of photo-catalytic activity of the perovskite SrTiO3 can be realized by Bi ions substituting for Sr ions, and Bi-based perovskite BiTiO3 will be a potential photocatalytic material.
关键词： band gap,electronic structure,density of states,absorption spectra,BixSr1-xTiO3
更新于2025-09-10 09:29:36
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Enhancing optical absorption in visible light of ZnO co-doped with europium and promethium by first principles study through modified Becke and Johnson potential scheme
摘要： By using first-principle calculations we studied the electronic, optical and magnetic properties of ZnO co-doped with Eu and Pm. In this calculation, we used Wien2k code based on Full potential linearized augmented plane waves (FP-LAPW) method with the modified Becke-Johnson (mBJ) approximation. This correction gives good band gap compared to experimental band gap. The introduction of Eu and Pm codoping leads to an increase in the band gap. Electrons can transit easily from the valence band to the conduction band, which results in an enhancement of visible light absorption in a wider absorption range. Absorption spectra reach a high value in visible and infrared light regions. With the significance of the obtained results, the studied compounds may potentially find spintronic and optoelectronic applications.
关键词： transmittance,Zinc Oxide,density functional theory,band gap,spintronics,Rare Earth,magnetic properties,absorption,modified Becke-Johnson,photovoltaic
更新于2025-09-10 09:29:36
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Phase transformation and luminescence properties of Y2.94Al5-xGaxO12: 0.06Ce3+phosphors
摘要： A series of Ga-substituted Ce3+-doped yttrium aluminum garnet (Y2.94Al5-xGaxO12: 0.06Ce3+) phosphors were synthesized at different atmospheres and temperatures. The structure, optical and thermal stability properties were analyzed using X-ray diffraction (XRD), photoluminescence (PL) and thermal measurements. A novel finding was revealed that gallium oxide (Ga2O3) was unstable in reducing atmosphere by XRD, and we explained the mechanism for the first time. In addition, it was found that Y3Al3Ga2O12 was formed due to Al3+ ions entering the lattice of Y3Ga5O12 gradually and the mechanism was clearly illustrated. The emission intensity of Y2.94Al5-xGaxO12: 0.06Ce3+ phosphors was determined by two aspects—the phase formation temperature and the band gap of host lattice. What’s more, introducing 6 wt% H3BO3 as flux can improve thermal stability to maximum extent and the thermal ionization model was used to explain the thermal quenching mechanism. Finally, the critical parameters including color rendering index (CRI), correlated color temperature (CCT), light efficiency of light emitting diodes (LEDs) packaged with the resultant green phosphors and red phosphors were studied.
关键词： thermal ionization,band gap,YAGG: Ce3+,phase transformation
更新于2025-09-10 09:29:36