Resonance Raman and photoluminescence excitation profiles and excited-state dynamics in CdSe nanocrystals

• Published in: The Journal of chemical physics 2013-07, Vol.139 (2), p.024702-024702
• Main Authors: Baker, Joshua A, Kelley, David F, Kelley, Anne Myers
• Format: Article
• Language: English
• Subjects: Cadmium Compounds - chemistry; Cadmium selenides; Electronics; Excitation; Intermetallics; Luminescence; Nanocrystals; Nanoparticles - chemistry; Phonons; Photoluminescence; Selenium Compounds - chemistry; Spectrum Analysis, Raman; Wavelengths
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4812499

Resonance Raman excitation profiles for the longitudinal optical (LO) phonon fundamental and its first overtone have been measured for organic ligand capped, wurtzite form CdSe nanocrystals of ∼3.2 nm diameter dissolved in chloroform. The absolute differential Raman cross-section for the fundamental is much larger when excited at 532 or 543 nm, on the high-frequency side of the lowest-wavelength absorption maximum, than for excitation in the 458-476 nm range although the absorbance is higher at the shorter wavelengths. That is, the quantum yield for resonance Raman scattering is reduced for higher-energy excitation. In contrast, the photoluminescence quantum yield is relatively constant with wavelength. The optical absorption spectrum and the resonance Raman excitation profiles and depolarization dispersion curves are reproduced with a model for the energies, oscillator strengths, electron-phonon couplings, and dephasing rates of the multiple low-lying electronic excitations. The Huang-Rhys factor for LO phonon in the lowest excitonic transition is found to lie in the range S = 0.04-0.14. The strong, broad absorption feature about 0.5 eV above the lowest excitonic peak, typically labeled as the 1P3∕21Pe transition, is shown to consist of at least two significant components that vary greatly in the magnitude of their electron-phonon coupling.