Raman scattering and photoluminescence (PL) emission are used to investigate a single layer of tungsten disulfide (WS${}_{2}$) obtained by exfoliating $n$-type bulk crystals. Direct gap with both neutral charged exciton recombination is observed in the low temperature PL spectra. The ratio between trion can be tuned simply varying excitation power. Moreover, intensity independently using additional subband laser excitation.

Synthetic two-dimensional transition metal dichalcogenides such as, tungsten disulphide (WS2), diselenide (WSe2), molybdenum (MoS2) as well mixed (Mo0.5W0.5S2) single crystals were grown by the chemical vapor transport method using halogens (bromine or chlorine) agents. Multi- layer samples cleaved from crystals, and their nonlinear optical (NLO) properties obtained both open aperture closed Z-scan measurements a picosecond mode-locked Nd: YAG laser operating at wavelength of 1064 nm, with...

Optical spectroscopy in high magnetic fields $B\leq65$ T is used to reveal the very different nature of carriers monolayer and bulk transition metal dichalcogenides. In WSe$_{2}$, exciton emission shifts linearly with field exhibits a splitting which originates from induced valley splitting. The data can be described using single particle picture Dirac-like Hamiltonian for massive Dirac fermions, an additional term phenomenologically include contrast, WSe$_{2}$ where inversion symmetry...

Resonant Raman spectra of single-layer ${\mathrm{WS}}_{2}$ flakes are presented. A second-order peak (2LA) appears under resonant excitation with a separation from the ${\mathrm{E}}_{2g}^{1}$ mode only ${4\mathrm{cm}}^{\ensuremath{-}1}$. Depending on intensity ratio and respective linewidths these two peaks, any analysis that neglects presence 2LA can lead to an inaccurate estimation position mode, leading potentially incorrect assignment for number layers. Our results show strongly depends...

Second harmonic generation (SHG) of a high intensity was found in MoS2 flakes different thicknesses exfoliated on silicon substrate. Reduction the SHG observed only for small portion flakes, both very thin and quite thick ones. This attributed to presence polytypism, i.e., 3R non-centrosymmetric 2H centrosymmetric polytypes, source bulk crystal grown by chemical vapor transport technique. The two polytypes sample confirmed spectral structure photoluminescence bound excitons at low...

Photoconductivity in \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ single crystals was observed the temperature range of 80--250 K. The energy gap, 0.89 eV at 85 K, and its dependence were determined. values average phonon energy, 55 meV, electron-phonon coupling parameter, S=2.75, evaluated. quenching photoconductivity is explained assuming two-center model. donor acceptor activation 70 120 respectively, as well hole mobility due to lattice scattering

A method that uses second-harmonic generation is applied to the study of oxidized Si(111) surface by in situ control thermal and synthetic oxide etching with monolayer atomic resolution. It shown thin layer adjacent Si (with a 5–10-Å thickness) exerts strong influence on reflected intensity. The contribution remaining bulk insignificant. Various contributions nonlinear polarization SiO2–Si interface, such as static electric field, inhomogeneous deformation, effect crystalline layer, are considered.

The mutual influence of the parametric and Raman mechanisms in generation higher Stokes components stimulated scattering is investigated theoretically experimentally for case second axial component. It shown that experimental results can be explained if allowance made mechanism even presence considerable wave mismatch.

Abstract Spinel‐type ZnGa 2 O 4 and ZnAl powders doped with Eu 3+ Tb ions, including dual doping, have been prepared by solid phase reactions deposition from chemical solutions. XRD analysis demonstrates the high quality of spinel grains constituting powder. The luminescence shows that rare earth ions are incorporated in defect regions at grain boundaries. emission spectra samples europium characterized an intense red region due to 5 D 0 → 7 F 1,2 transitions whereas case terbium highest...

Diphenylalanine peptide nano- and microtubes formed by self-assembly demonstrate strongly enhanced tunable single-photon two-photon luminescence in the visible range, which appears after heat- or laser treatment of these self-organized microtubes. This process significantly extends functionality microstructures can trigger a new interest optical properties structures based on short peptides.

Optical absorption, photoacoustic spectroscopy and photoconductivity were investigated in ReS2 single crystals the temperature range 50–300 K. The energy gap (1.55 eV at 80 K) its dependence, value of average phonon (17 meV) electron coupling parameter (S=2.40) as well electron-hole mobility due to lattice scattering determined.

The transfer matrix method has been widely used to calculate wave propagation through the layered structures consisting entirely of either linear or nonlinear optical materials. In present work, we develop for alternating layers and result is presented in a form that allows one directly substitute values material constants, refractive index absorption coefficient, into expressions describing second harmonic generation (SHG) field. model applied calculation (SH) field generated nano-thin...

The optical properties of the chromium doped spinel type semiconductor α-ZnAl2S4 have been examined over temperature range 2–540 K. intrinsic photoluminescence (PL) showed an intense ultraviolet peak at 381 nm 296 From extrinsic absorption and emission spectra transitions between ground state A2g4 excited levels Eg2, T1g2, T2g2, T2g4, T1g4 Cr3+ ions were observed. A fit measured dependence PL decay, using a four level model, yielded lifetimes T2g4 energy gaps Eg2–T1g2 Eg2–T2g4 states which...

Photoluminescence was observed in both synthetic and natural forms of the transition metal dichalcogenide ${\mathrm{MoS}}_{2}.$ The emission is near infrared between 0.8 1.2 eV. Two distinct regions were identified. first region, centered at 1.18 eV only material, produced by bound excitons related to halogen transport agent intercalated within layers during growth process. second weaker consisting a broad band 0.95 believed be caused deep donor center, molybdenite.

Radiative recombination processes in the transition metal dichalcogenide compound $2H\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ are investigated. The strong sharp line photoluminescence spectral range 1.32--1.34 eV is attributed to of excitons bound on electron-attractive neutral centers, formed by ${\mathrm{Br}}_{2}$ molecules intercalated van der Waals gap layered crystals. These located at energy ${E}_{T}=0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ below conduction band, display properties...

This publisher's note amends the Funding section of a recent publication [Opt. Express24, 20685 (2016].

Abstract Multilayer MoS 2 , MoSe and WSe crystals were excited with femtosecond optical pulses of various wavelengths. The emitted terahertz (THz) radiation found to be the most intense at photon energies coinciding direct energy gap K points Brillouin zone corresponding materials. It was shown that transition metal dichalcogenides different dopant type emit THz opposite polarity, suggesting surface field plays a role in emission. Nevertheless, pump–THz probe experiments contradicted...