Jean Ebothé

Several features of emission spectra of Pr+3 ions incorporated into Li2B4O7 glass matrices

Influence of lithium tetraborate (Li2B4O7, TBL) glass matrix on the luminescent properties of the Pr+3 ions emission was investigated. It was demonstrated that the decrease of matrix long-range ordering leads to substantial widening of corresponding peaks in the emission spectra in comparison with crystalline Ca4GdO(BO3)3 matrices. During the decrease of temperature from 292 down to 82K a distinct low-energy spectral shift of the principal red luminescent band from 607to610nm is observed, which is a consequence of a coexistence of several structural borate fragments. Simulations of incorporation the Pr3+ ions into the TBL glasslike matrix were carried out using the Langevin molecular dynamics simulations and quantum chemical simulations. Possibility of partial substitution of boron ions by Pr3+ ions is demonstrated. The contribution of the electron-phonon subsystems to the spectral broadening of the corresponding emission red lines was evaluated. It was shown that the main contribution to the emission ban...

Acoustically induced optical second harmonic generation in Pb4.7Ba0.3Ge3O11 crystals

Acoustically induced optical second harmonic generation (AIOSHG) in ferroelectric Pb4.7Ba0.3Ge3O11 (PBG) crystal has been observed. With increasing acoustical power, the AIOSHG for Nd doped yttrium–aluminum garnet laser light (λ=1.06 μm) increases and achieves its maximum value at acoustical power density of about 1.75 W/cm2. The values of the AIOSHG for the PGB are considerably higher than for other photorefractive ferroelectrics. With decreasing temperature, the AIOSHG signal strongly increases below 29 K and correlates well with a ferroelectric phase transition detected by the differential scanning calorimetric method and spontaneous polarization measurements. The AIOSHG maxima were observed at acoustical frequencies lying within the ranges 12–17, 22 to 23, and above 26 kHz. Comparing the obtained results with the acoustically induced Raman spectra at different temperatures one can conclude that the effect is caused prevailingly by acoustically induced electron–phonon anharmonicity, which is larger in ...

Modeling of optical and electrical behavior of semiconducting thin films: Application to sprayed CdS on transparent substrates

Both the optical absorption coefficient α, and the carrier density N, of semiconducting thin films are analytically investigated in relation with their deposition substrate influence. It is shown that these two properties are sensitive to the film thickness d, particularly when incident monochromatic light is very close to the film transmission cutoff wavelength. α behaves according to the α≊f(d−1) type of function while N obeys the law N≊f(d−m) whose precise form varies with m value and depends on the substrate influence. Experimental results report on sprayed CdS films respectively deposited on glass, SnO2, and ITO substrates which illustrate the suitability of the model proposed. The film absorption coefficient is affected by the migration phenomenon at the film‐substrate interface, the rate of the migration depending upon the substrate involved. m≊1 obtained with SnO2 and m≊2 with ITO indicate different CdS film interface properties, typical of the substrate used.

Nanoscale Topography and Magnetic Structure of Nanocrystallized Nickel Electrodeposits

The microstructure and magnetic properties of nickel films thick of 100 till 1000 nm are here investigated. They are deposited on polycrystalline Cu substrate by cathodic voltammetry (CV) technique varying the scan rate in the interval 0.17 ≤ r ≤ 1.67 mV/s. Thicker and rougher samples grow at lower r values while thinner and smoother ones are obtained at the higher r values. All the samples obtained exhibit a negative strain indicating a compressive stress that decreases with the film thickness increase. The magnetic reversal of the Ni films is ruled by the spin rotation mechanism associated with their low squarness of about 28%. The study of their ferromagnetic-topography dependence reveals that their magnetic domains always remain of the Néel type (MD)N in the investigated r values according to the model of Zhao et al. [J. Appl. Phys. 89, 1325(2001)]. The magnetic anisotropy of the Ni samples exhibit a out-of-plane component that becomes sensitively marked with the increase of the film thickness.

Magnetic properties of nanocrystallized nickel films on gold substrate deposited by cathodic voltammetry: Scan rate induced effects

Ni electrodeposits of thickness values ranged from 70 nm till about 1.20 μm and grown on gold substrate by cathodic voltammetry (C-V) technique are investigated varying the scan rate (r) of the related (C-V) curves in the interval 0.167<r<1.67 mV/s. The system engenders thinner films having rougher surfaces for higher r values while lower ones leads to thicker and smoother samples. Their magnetic reversal is ruled by the domain wall (DW) nucleation and motion. Their ferromagnetic-topography dependence reveals the existence of a critical thickness dc∼375 nm for both their microstructure and magnetic nanostructure. Their magnetic domain sizes (w) evolution with the sample roughness is typical of the Bloch domain type (MD)B below dc while the Neel type (MD)N appears beyond dc according to the topography-based model of Zhao et al. [J. Appl. Phys. 89, 1325 (2001)]. The magnetic anisotropy of the Ni samples exhibits a predominant parallel component for the thinnest sample while the perpendicular one grows with ...

Hole‐diffusion length and transport parameters of thin CdS films from a Schottky barrier

The optoelectronic and transport properties of thin sprayed CdS films, having a thickness of less than 2 μm are reported. The use of two independent technics, surface photovoltage and photoelectrochemical measurements, led to a good agreement in the hole‐diffusion length values. These range from 0.017 to 0.15 μm and behaved differently in two zones. A rapid increase of this parameter is observed below a film thickness of 0.4 μm. Above this thickness, the value obtained is constant. Specific space‐charge widths are expected because of the respective measurement conditions. The hole‐diffusion length decreases as carrier density increases. The hole lifetime shows a regular decrease as the thickness factor increases, while the hole‐diffusion coefficient and mobility patterns are similar to that of the photocurrent.