[en] Using generalized Ginzburg-Devonshire theory, the behavior of the ferroelectric thin film coated with two metallic electrodes with the larger polarization near surface vicinity than that of bulk is studied. The effects of the imperfect surface layer are to change polarization, produce non-uniform polarization distribution and raise the phase transition to higher temperature. The asymmetric electric hysteresis loop is obtained

[en] In this study, the valence state of Pr in Mg doped PrGaO₃ perovskites was investigated. It is found that Pr⁴⁺ ions are created in samples doped with low-valence ions, for example, with Mg²⁺. The color of the doped samples changes from black to light green after being treated in H₂ atmosphere, which shows that the Pr⁴⁺ ions in the sample are reduced to Pr³⁺ ions. The open circuit voltage of the solid oxide fuel cell (SOFC) using PrGa_0.95Mg_0.05O₃ as the electrolyte increases with time and the X-ray photoelectron spectroscopy (XPS) data of PrGa_0.9Mg_0.1O₃ also show the existence of Pr⁴⁺ ions in Mg doped PrGaO₃

[en] Shock waves in unconfined aluminium films of varying thicknesses from 3 to 10 μm induced by a single fs-laser-pulse with a full width half maximum width of about 130 fs at λ = 800 nm wavelength have been investigated by using ultrafast microscopy. With successive sub-picosecond-resolved micrographs of the aluminium/α-quartz interface taken at various probing times, the shock transit time in aluminium films of different thicknesses was measured accurately. From the best linear fit of the transit time versus the thickness of aluminium films, the shock velocity was measured to be 9.0 ± 0.4 km s^-1 at the laser intensity of 7.84 x 10¹³ W cm^-2. From the shock velocity D the shock pressure P and temperature T were calculated to be 69 ± 5 GPa and 1852 ± 400 K, respectively. Experimental results in good agreement with previous theoretical and experimental works indicate that the time-resolved ultrafast microscopy technique is a fairly accurate and feasible technique for studying fs-laser-driven shock waves in opaque thin films.

[en] Upconversion luminescence was obtained from CdSeS nanocrystals (NCs) under 800 nm femtosecond laser excitation. The structural and optical characteristics of the CdSeS NCs were investigated experimentally by use of UV–visible absorption spectroscopy, transmission electron microscopy, X-ray diffractometry, and time-resolved luminescence dynamics. Peak shift of luminescence in CdSeS NCs can be readily observed under different wavelength femtosecond excitation. The pump power dependence of the luminescence intensity and time-resolved decay revealed that one, two, and three-photon absorption occur. It was found that upconversion luminescence is composed of photoinduced trapping and a band-edge excitonic state, and two types of species are involved in the biexponential luminescence decay kinetics. With increasing Se-doped composition, luminescence lifetimes of CdSeS NCs with similar sizes become shorter. This is not consistent with the changes of undoped CdS NCs and is ascribed to impurity level increased doping in the energy gap, which is favorable for trapping luminescence. A simple energy level of doping NCs is used to interpret upconversion luminescence and the peak shift of steady-state emission.

[en] The results of Er³⁺ ion spectroscopic analysis in Sc:LiNbO₃ crystals were reported. The line strengths from the ground state to the excited state were evaluated from the measured unpolarized absorption spectrum and analyzed by using standard Judd-Ofelt theory. For Sc(3 mol. %):Er (1 mol. %):LiNbO₃ crystal, the obtained intensity parameters are: Ω₂=3.72 x 10^-20 cm², Ω₄=1.07 x 10^-20 cm², and Ω₆=0.98 x 10^-20 cm². The fluorescence spectra and microsecond time-resolved spectra were investigated in the visible region. The excited state absorption transition strengths at 800 nm excitation were evaluated based on Judd-Ofelt theory. The results obtained here were compared to results from other research on Er:LiNbO₃ crystals. (orig.)

[en] The transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure is reported. The transient process of the system, which is induced by the external coherent coupling field, shows the property of no inverse gain. We find that the transient behavior of the probe field can be tuned by the change of tunneling barrier. Both the amplitude of the transient gain and the frequency of the oscillation can be affected by the lifetime broadening

[en] Observed is 15 times enhancement of Ho³⁺ green upconversion (UC) emission in Ho³⁺(0.75 mol %)/Nd³⁺(0.75 mol %) doped lithium niobate crystal after incorporating with 4 mol % of Yb³⁺ under 800 nm femtosecond laser excitation. Yb³⁺ acting as bridging ion increases the energy transfer efficiency from Nd³⁺⁴F_3/2 level to Ho³⁺ in these triply doped systems. The nonradiative energy transfer efficiency from Nd³⁺⁴F_3/2 to Yd³⁺²F_5/2 level can reach to 56%. The UC emission mechanisms are proposed based on spectral, kinetic, and pump power dependence analyses. The green UC emission is accomplished through a multi-ion interaction involving ground state absorption by the Nd³⁺ (⁴I_9/2→²H_9/2,⁴F_5/2) followed by three successive energy transfer processes involving one Nd³⁺-Yb³⁺ (⁴F_3/2+²F_7/2→⁴I_9/2+²F_5/2) and two Yb³⁺-Ho³⁺ pairs (²F_5/2+⁵I₈→²F_7/2+⁵I₆ and ²F_5/2+⁵I₆→²F_7/2+⁵S₂,⁵F₄); whereas the red is dominated by excited state absorption of the Ho³⁺ (⁵I₇→⁵F₅) following two successive energy transfer processes involving the Nd³⁺-Yb³⁺ (⁴F_3/2+²F_7/2→⁴I_9/2+²F_5/2) and Yb³⁺-Ho³⁺ pairs (²F_5/2+⁵I₈→²F_7/2+⁵I₆) followed by the Ho³⁺ nonradiative relaxation to ⁵I₇

[en] The aqueous CdTe quantum dots (QDs) were synthesized by the electrostatic reaction method. The optical properties of CdTe QDs were investigated by femtosecond Z-scan and time-resolved luminescence technique in nonresonant spectral region. The nonlinear absorption and refraction are ascribed to two-photon absorption, and time-resolved upconversion photoluminescence produces biexponential decay pattern at infrared femtosecond laser excitation. Upconversion luminescence is composed of a band-edge excitonic state and a photoinduced trapping state. The short-lived band-edge excitonic emission is independent of the detection wavelengths, and long-lived species becomes even longer with the increase of detection wavelengths, which indicates the size dependence of surface excitonic emission.

[en] We present a Judd-Ofelt spectroscopic analysis on the Mg/Er-codoped congruent lithium niobate (LiNbO₃) crystals. The Judd-Ofelt model is applied to the room temperature unpolarized absorption intensities of Er³⁺ ions on eleven transition bands to determine their intensity parameters: Ω₂=2.36x10^-20 cm², Ω₄=0.76x10^-20 cm², Ω₆=0.30x10^-20 cm² in Er:LiNbO₃ crystal heavily codoped with MgO. The radiative lifetime of ²H_9/2 becomes longer when MgO is added into Er:LiNbO₃ crystal. The experimental lifetimes are obtained using microsecond time-resolved spectra at 400 nm femtosecond pulse excitation to predict radiative quantum efficiency. Combining higher radiative quantum efficiency with longer radiative lifetime, we conclude that Mg/Er-codoped LiNbO₃ crystals are more suitable than Er: LiNbO₃ ones in laser materials