Nonlinear Optical Properties of 2D CdSe Nanoplatelets in a Nonresonant Regime
Igor M. Gonçalves, Anusri Medda, Alyson J. A. Carvalho, Cecília L. A. V. Campos, Soubhik Ghosh, Anderson S. L. Gomes, Amitava Patra
Abstract
The nonlinear optical response of CdSe and CdSe/CdS core/shell nanoplatelets (NPLs) in toluene suspension was determined by using Z-scan and optical Kerr gate (OKG) techniques at 800 nm in the femtosecond regime. First, an analysis of the nonlinearities based on the Z-scan resulted in n 2 = 1.4 × 10 –16 cm 2 /W and n 2 = 1.3 × 10 –16 cm 2 /W for CdSe and CdSe/CdS core/shell NPLs, respectively. Fifth-order nonlinear absorption behavior was predominant, resulting in α 4 = 4.0 × 10 –2 cm/GW for CdSe NPLs and α 4 = 9.0 × 10 –3 cm/GW for CdSe/CdS core/shell NPLs for an optical intensity of 60.97 and 122 GW/cm 2, respectively. The nonlinear refractive index obtained from Z-scan is in good agreement with those obtained from the OKG, and the response time obtained from OKG showed a decay of less than 1 ps for all studied materials, about 5 times slower than the pulse duration. For optical intensities in the range between 30.45 and 182.8 GW/cm 2, NLA was not observed for toluene but was observed for CdSe and CdSe/CdS core/shell NPLs, revealing that the presence of the NPLs decreases the threshold of the absorptive nonlinearity. The results are discussed and explained based on the well-known materials’ electronic structure.