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dz2 Orbitals Mediated Bound Magnetic Polarons in Ferromagnetic Ce Doped BaTiO3 Nanoparticles and its Enriched Two Photon Absorption Cross Section
摘要： Enriched ferromagnetism and two photon absorption (TPA) cross section of perovskite BaTiO3 nanoparticles are indispensible for magnetic and optical data storage applications. In this work, the hydrothermally synthesized Ce doped BaTiO3 nanoparticles exhibit the maximum room temperature ferromagnetism (4.26×10-3 emu/g) at 4 mol% due to the increase of oxygen vacancies as evidenced by X-ray photoelectron, electron spin resonance spectroscopies and density functional theory (DFT) calculations. Hence, the oxygen vacancy constituted bound magnetic polaron (BMP) model has been invoked to explain the enhancement of ferromagnetism. BMP theoretical model indicates the increase of BMP magnetization (M0, 3.0 to 4.8×10-3 emu/g) and true spontaneous moment per BMP (meff, 4 to 9.88×10-4 emu) on Ce doping. DFT calculations show that BMPs mediate via Ti d orbitals leading to the ferromagnetism. Besides, it is understood that the magnetic moment induced by Ce at Ba site is higher than Ce at Ti site in the presence of oxygen vacancies. Open aperture Z-scan technique displays the highest TPA coefficient β (7.08×10-10 m/W) and TPA cross section σTPA (455×104 GM) at 4 mol% of Ce as a result of robust TPA induced excited state absorption. A large σTPA is attributed to the longer excited state lifetime τ (7.63 ns) of charge carriers created by oxygen vacancies and Ce ions which encounter several electronic transitions in the excited sub-states.
关键词： Ce doping,oxygen vacancies,bound magnetic polarons,two photon absorption,DFT calculations,Z-scan technique,BaTiO3 nanoparticles,ferromagnetism
更新于2025-11-19 16:56:35
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Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites
摘要： Among the exceptional properties of lead halide perovskites (LHPs) is the ultraslow cooling of hot carriers. Carrier densities below the Mott density for large polarons (≤ ≈1018 cm?3) are focused on here. As in other semiconductors, a nascent hot electron distribution initially cools down via emission of longitudinal optical (LO) phonons on the 10?14–10?13 s timescale. What distinguishes LHPs from conventional semiconductors is the exceptionally efficient screening in the former. The dielectric screening in LHPs on the 10?13 s timescale results in an order-of-magnitude reduction in the Coulomb potential upon the formation of a large polaron, likely with ferroelectric-like local ordering. Further LO-phonon emission is inhibited, and this leads to partial retention of hot electron energy on the 10?12 s timescale, more so in hybrid LHPs than in their all-inorganic counterparts. Further cooling of hot polarons occurs on the 10?10 s timescale, and this can be attributed to the slow diffusion of heat out of the large polaron volume due to the low thermal conductivity of LHPs. Like other carrier properties, slow hot carrier cooling in LHPs can be intimately related to efficient screening in a soft, anharmonic, and dynamically disordered lattice.
关键词： dielectric function,lead halide perovskites,screening,hot electrons,large polarons
更新于2025-09-19 17:15:36
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Phonon and Polaron properties in InSb spherical quantum dots
摘要： The size-dependent energy gaps, electron and heavy hole effective masses, phonon frequencies and polaron related parameters in InSb spherical quantum dots are investigated. The calculations are performed using a pseudopotential approach. Good agreement is obtained between our results and those of the literature for bulk InSb. When proceeding from bulk to nano-scale, all studied properties are found to be changed significantly. This is attributed to the quantum confinement effect.
关键词： Polarons,Phonons,Quantum dots,InSb,Quantum confinement
更新于2025-09-19 17:13:59
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Influence of Oxygen Vacancy Density on the Polaronic Configuration in Rutile
摘要： Polaronic con?gurations that were introduced by oxygen vacancy in rutile TiO2 crystal have been studied by the DFT + U method. It is found that the building block of TiO6 will expand when extra electron is trapped in the central Ti atom as polaron. With manually adjusting the initial geometry of oxygen vacancy structure, a variety of polaronic con?gurations are obtained after variable-cell relaxation. By calculating different sizes of supercell model, it is found that the most stable con?guration can be in?uenced by the density of oxygen vacancy. With increasing interaction between vacancies, the most stable polaronic con?guration change from small polaronic con?guration to mixed con?guration.
关键词： DFT + U,rutile,electronic structure,oxygen vacancies,polarons
更新于2025-09-10 09:29:36
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Polarons, bipolarons, and absorption spectroscopy of PEDOT
摘要： Electronic structure and optical absorption spectra of poly(3,4-ethylenedioxythiophene) (PEDOT) for different oxidation levels were studied using density functional theory (DFT) and time-dependent DFT. It is shown that the DFT-based predictions for the polaronic and bipolaronic states and the nature of corresponding optical transitions are qualitatively different from the widely used traditional picture based on semi-empirical pre-DFT approaches that still dominate the current literature. Based on the results of our calculations, the experimental Vis/NIR absorbance spectroscopy and the electron paramagnetic resonance spectroscopy are re-examined and a new interpretation of the measured spectra and the spin signal which is qualitatively different from the traditional interpretation is provided. The findings and conclusions concerning the nature of polaronic and bipolaronic states, band structure and absorption spectra presented for PEDOT, are generic for a wide class of conducting polymers (such as polythiophenes and their derivatives) that have similar structure of monomer units.
关键词： Vis/NIR absorbance spectroscopy,PEDOT,conducting polymers,Polarons,electron paramagnetic resonance spectroscopy,bipolarons
更新于2025-09-04 15:30:14