title: Resonance Raman and photoluminescence excitation profiles and excited-state dynamics in CdSe nanocrystals.
abstract: 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.
authors.affiliation: Chemistry and Chemical Biology, University of California, Merced, 5200 North Lake Road, Merced, California 95343, USA.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Baker
authors.forename: David F
authors.initials: DF
authors.lastname: Kelley
authors.forename: Anne Myers
authors.initials: AM
authors.lastname: Kelley
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D049449:Luminescence; D053758:Nanoparticles / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; C058667:cadmium selenide