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Abstract Lead-free ferroelectric Bi 0.5 Na 0.5 TiO 3 (BNT) has attracted considerable attention taking into account environment issues and applications in micro electro mechanical systems. The effects of manganese (Mn) substitution on microstructure, lattice dynamics, and optical properties of BNT films have been investigated by X-ray diffraction, Raman scattering and ellipsometric spectra. The phase transitions as a function of temperature have been systemically explored by temperature-dependent Raman and ellipsometric spectra. The anomalous temperature-dependent behavior of Raman-active modes suggests that there is an intermediate phase between ferroelectric rhombohedral and paraelectric tetragonal phase, which is confirmed by the temperature-dependent optical band gap (E g) and extinction coefficient (κ) extracted from ellipsometric spectra analysis. And then, a phase diagram as a function of Mn composition has been proposed. Finally, we demonstrate that Mn-dopant is an effective approach to enhance ferroelectric properties, improve energy storage ability, and increase permittivity as well as suppress leakage current. Electrical dielectric responses indicate that there is a critical frequency and polarization relaxation behavior in the films. The present results will be helpful for the application of BNT-based lead-free multifunctional devices. Highlights • Mn-doped Bi 0.5 Na 0.5 TiO 3 films are probed by Raman and ellipsometric spectra. • Mn-dopant is an effective approach to enhance ferroelectric properties. • Mechanism of leakage current in different electric field regions are proposed. [ABSTRACT FROM AUTHOR]

We present a new paradigm for understanding optical absorption and hot electron dynamics experiments in graphene. Our analysis pivots on assigning proper importance to phonon-assisted indirect processes and bleaching of direct processes. We show indirect processes figure in the excess absorption in the UV region. Experiments which were thought to indicate ultrafast relaxation of electrons and holes, reaching a thermal distribution from an extremely nonthermal one in under 5-10 fs, instead are explained by the nascent electron and hole distributions produced by indirect transitions. These need no relaxation or ad-hoc energy removal to agree with the observed emission spectra and fast pulsed absorption spectra. The fast emission following pulsed absorption is dominated by phonon-assisted processes, which vastly outnumber direct ones and are always available, connecting any electron with any hole any time. Calculations are given, including explicitly calculating the magnitude of indirect processes, supporting these views. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic and laser properties of Yb3+ in ceramic Y2O3 have been studied at room and cryogenic temperatures. Laser performance is very substantially improved by cooling to liquid nitrogen temperature, primarily due to the great reduction in ground state absorption that permits laser operation on the much stronger 1030-nm emission line rather than the 1077-nm line. The 976-nm “zero line” is observed to become much weaker as the temperature is reduced. Several models for this behavior are considered, but none adequately explains this surprising result. Spectroscopy of Yb:Sc2O3 indicates that it is likely to be an even better cryogenic gain material, given samples of comparable optical quality. [Copyright &y& Elsevier]