Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 54, Issue 4, Pages 1185-1189Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201409837
Keywords
fluorescence; gallium selenide; photoluminescence; second harmonic generation; two-dimensional materials
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Funding
- PolyU Project of Strategic Importance [1-ZE14]
- HKU/PolyU, HKUST Collaborative Research Fund (CRF) [HKU9/CRF/13G]
- HKU/PolyU, HKUST Collaborative Research Fund (PolyU) [E-RD50]
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Gallium selenide, an important second-order nonlinear semiconductor, has received much scientific interest. However, the nonlinear properties in its two-dimensional (2D) form are still unknown. A strong second harmonic generation (SHG) in bilayer and multilayer GaSe sheets is reported. This is also the first observation of SHG on 2D GaSe thin layers. The SHG of multilayer GaSe above five layers shows a quadratic dependence on the thickness; while that of a sheet thinner than five layers shows a cubic dependence. The discrepancy between the two SHG responses is attributed to the weakened stability of non-centrosymmetric GaSe in the atomically thin flakes where a layer-layer stacking order tends to favor centrosymmetric modification. Importantly, two-photon excited fluorescence has also been observed in the GaSe sheets. Our free-energy calculations based on first-principles methods support the observed nonlinear optical phenomena of the atomically thin layers.
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