Linearly Polarized Remote-Edge Luminescence in GaSe Nanoslabs

Abstract

We report highly linearly polarized remote luminescence that emerges at the cleaved edges of nanoscale gallium selenide slabs tens of micrometers away from the optical excitation spot. The remote-edge luminescence (REL) measured in the reflection geometry has a degree of linear polarization above 0.90, with polarization orientation pointing toward the photoexcitation spot. The REL is dominated by an index-guided optical mode that is linearly polarized along the crystalline c-axis. This luminescence is from out-of-plane dipoles that are converted from in-plane dipoles through a spin-flip process at the excitation spot.

Layer- and frequency-dependent second harmonic generation in reflection from GaSe atomic crystals

“…For nanoslabs with the same number of layers, we find that the sample-to-sample variance of the SHG power is typically ±50%. Our results suggest that χ (2) drops from 6 L to 3 L by a factor of 3 and increases from 3 L to 2 L by a factor of 2.0±0.7. For 2 L and 1 L, the values of χ (2) are similar within the sample-to-sample variance.…”

“…In light of the absence of such an alternation in SHG in- tensity with layer thickness in our few-layer samples, we rule out a stacking change from -stacking to β-stacking as the primary source of the decrease in SH efficiency in few-layer GaSe. The deviation of the measured values of χ (2) from the model based on constant χ (2) occurs for thickness 7 L, where the electronic band structure is calculated to increase dramatically from its bulk value 6,7,15 . This suggests that the reduction of χ (2) in few-layer GaSe may be a signature of such changes in the band structure.…”

“…3b) accounting for interference in the multilayer system 24,25 composed of vacuum (V), a d G -thick GaSe slab (G), a d O (90 nm)-thick SiO 2 (O) layer, and a Si (S) substrate. The nonlinear optical response of the GaSe slab can be understood in terms of the second-order polarization P (2) ,…”

“…, it is sufficient to calculate P (2) for fundamental electric field polarization along the GaSe x-axis (a-axis), for which P (2) = P (2)ŷ .…”

Enhanced Light Emission from the Ridge of Two-Dimensional InSe Flakes

“…1b). [22][23][24][25] This forbidden transition for normally incident excitation, only allowed by mixing with the deeper valence bands with Se pxy character or by excitation with excess photon energy, hinders potential nanoscale optoelectronic applications based on InSe in which a response to normally incident light is often required. Previously, InSe flakes were coupled to a silica-nanoparticles-roughened substrate to increase the coupling to the normally incident light, resulting in the enhancement of both light absorption and emission.…”