Excitation energy dependent ultrafast luminescence behavior of CdS nanostructures

in: ACS Photonics (2017)
Karras, Christian; Röder, Robert; Paa, Wolfgang; Ronning, Carsten; Stafast, Herbert
Cadmium sulfide (CdS) nanostructures were excited under ambient conditions by femtosecond (fs) laser pulses (380 nm<lambda_ex < 440 nm, tau=50 fs, rep. rate = 1 kHz, fluence<6.7 mJ/cm2). Their luminescence spectrum was recorded in the 490 nm< lambda:em<530 nm wavelength range during 0 < delta_t < 16 ps at 150 fs time resolution using optical Kerr gating (OKG). The emission spectrum and its kinetics (emission build-up and decay) were investigated as a function of the excitation energy (photon energy and fluence). The detected CdS emission onset delay can be adjusted between 0.1 ps to 2.8 ps relative to the excitation pulse: This delay decreases with decreasing h*lambda_ex and increasing fluence values and is attributed to the thermalization of the laser excited hot charge carriers. The observed light is mainly assigned to stimulated emission by an electron hole plasma (EHP). Thus, OKG allows to thoroughly study the ultrafast carrier and emission kinetics of highly excited semiconductors.

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