Local field effects in ultrafast light–matter interaction measured by pump-probe spectroscopy of monolayer MoSe2

Using ultrafast resonant pump-probe spectroscopy in an unconventional experimental setup we investigate the spectral shape and dynamics of absorption features related to the A exciton in an hexagonal boron nitride (hBN)/MoSe2/hBN van der Waals heterostructure. While in a pure two-level system a pump-probe experiment measures the occupation or the polarization dynamics, depending on the time ordering of the pulse pair, in the transition metal dichalcogenide (TMD) system both quantities get thoroughly mixed by strong exciton–exciton interaction. We find that for short positive delays the spectral lines experience pronounced changes in their shape and energy and they relax to the original situation on a picosecond time scale. For negative delays, distinctive spectral oscillations appear indicating the first-time observation of perturbed free induction decay for a TMD system. The comparison between co-circular and cross-circular excitation schemes further allows us to investigate the rapid inter-valley scattering. By considering a three-level system as a minimal model including the local field effect, excitation-induced dephasing (EID), and scattering between the excited states we explain all phenomena observed in the experiment with excellent consistency. Our handy model can be even further reduced to two levels in the case of a co-circular excitation, for which we derive analytic expressions to describe the detected signals. This allows us to trace back the spectral shapes and shifts to the impact of local field effect and EID thus fully reproducing the complex behavior of the observed effects.

Temperature Dependence of the Local Field Effect in YAG:Ce3+ Nanocomposites

The spontaneous emission rate (SER) of a chromophore in a nanoparticle (NP) is determined by the modification of the electric field by its environment. Previous studies of this local field...

A new strategy of interlayer doping of Li ions for the photoluminescence enhancement of Eu3+-doped bismuth oxychloride layered semiconductors

The interlayer doping of Li+ ions significantly improves the IEF in layered BiOCl, which modifies the photoluminescence of Eu3+ ions via its local field effect and photocarrier separation role.

Facile One-Step Synthesis and Enhanced Optical Nonlinearity of Graphene-γMnS

Graphene-γMnS were prepared by facile one-step hydrothermal method. Structures and properties of samples were explored by characterization, and nonlinear optical (NLO) enhancement of nanocomposites (NCs) was fully studied. Nanoparticles and NCs were tested at 532 nm by a Z-scan technique. With γMnS attached in G layers, NLO susceptibility of graphene-γMnS was greatly improved under single-pulse laser irradiation compared with G and γMnS. The nonlinearity enhanced was attributed to local field effect and charge transfer between γMnS and graphene layers. And NLO property enhancement was restricted by non-radiative defects in graphene-γMnS. Exploring the mechanism of nonlinearity enhancement was significant for fabrication of NLO devices. However, the optical nonlinearity decreased first and then increased with further increased addition of GO, because the dispersion of γMnS attached on graphene surface might make density of sp2 fragment and defects changed. Graphene-γMnS exhibited excellent and tunable NLO performance, illustrating that NCs materials have potential applications in NLO devices.

Time resolved femtosecond spectroscopy of nanocomposites

Characterization methods of nanocomposites consisted of semiconductor metal-oxide quantum dots (QD) incorporated into a dielectric matrix have been elaborated on the base of time resolved four-wave mixing and photon echo. Large permanent dipole moment, inherent to QDs under study, local field effect, the QD spatial dispersion and distribution function of the transition dipole moments in QDs are taken into account. New responses at multiple frequencies in directions differed from spatial synchronism conditions of well-known signals have been predicted.

Local Field Effect in antimony-germanate glasses co-doped with Rare-Earth ions and silver nanoparticles

The article presents the possible mechanisms of interaction between emission of Eu3+ ions and surface plasmon resonance (SPR) from Ag0 nanoparticles. The antimony-germanate glasses were synthetized by standard melt-quenching method. The influence of high-phonon glass forming compounds on excitation and luminescence spectra was analysed. Also, we showed that Sb2O3 is a mild reducing agent of noble metal ions. This mild reduction property enables thermochemical reduction of Ag+ to Ag0 in a single-step during the melting process. The energy transfer mechanisms between Eu3+ ions and Ag0 nanoparticles were also discussed in terms of local field effect of Ag0 nanoparticles. Full Text: PDF ReferencesS. Chatterjee, S. K. Saha, and D. Chakravorty, "Glass-Based Nanocomposites" in Glass Nanocomposites, B. Karmakar, K. Rademann and A. L. Stepanov, (Eds.: William Andrew Publishing, Boston, 2016) DirectLink D. Dorosz, et al., "Structural and optical study on antimony-silicate glasses doped with thulium ions", Spectrochim. Acta A 134, 608 (2015). CrossRef J. Zmojda, et al., "Effect of GeO2 content on structural and spectroscopic properties of antimony glasses doped with Sm3+ ions", J Mol. Struct. 1126, 207 (2016) CrossRef J. Zmojda, D. Dorosz, M. Kochanowicz, J. Dorosz, "Spectroscopic properties of Yb3+/Er3+ - doped antimony-phosphate glasses for fiber amplifiers", Phot. Lett. Poland 2, 76 (2010) CrossRef M. Eichelbaum and K. Rademann, "Plasmonic Enhancement or Energy Transfer? On the Luminescence of Gold-, Silver-, and Lanthanide-Doped Silicate Glasses and Its Potential for Light-Emitting Devices", Adv. Funct. Mater. 19, 2045 (2009) CrossRef Binnemans, K. Coord. "Interpretation of europium(III) spectra", Chem. Rev. 295, 1 (2015) CrossRef S. Selvi, K. Marimuthu, N. S. Murthy, G. Muralidharan, "Red light generation through the lead boro?telluro?phosphate glasses activated by Eu3+ ions", J Mol. Struct. 1119, 276 (2016) CrossRef J. Zmojda, et al., "Optical Characterization of Nano- and Microcrystals of EuPO4 Created by One-Step Synthesis of Antimony-Germanate-Silicate Glass Modified by P2O5", Materials 10, 1059 (2017) CrossRef N. Shasmal, B. Karmakar, "Enhancement and tuning of photoluminescence properties in Pr3+/Au co-doped antimony oxide glass nanocomposites by thermal treatment", J Alloy. Compd. 688, 313 (2016) CrossRef