Raman and ultrafast optical spectroscopy of acoustic phonons in CdTe0.68Se0.32 quantum dots

A.V. BRAGAS; C. AKU-LEH; R. MERLIN

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2006 vol. 73 p. 1 - 5

0163-1829

Acousticlike vibrations were observed in spontaneous Raman measurements on CdTe0.68Se0.32 quantum dots embedded in a borosilicate matrix and ascribed to the l=0, l=2, and l=1 modes of a spherical particle. Pump-probe stimulated Raman measurements on the same sample reveal only the symmetric l=0 mode, the frequency of which increases as the laser central energy moves to higher energies. Consistent with the strong dependence of the exciton energy on the particle size, such a behavior is attributed to resonant size-selective excitation of nanocrystallites whose absorption edge coincides with the central energy of the optical pulses. This selectivity, relying on the existence of double-resonant terms in the generation process, is not observed in spontaneous Raman scattering for which the resonances involve a single term.0.68Se0.32 quantum dots embedded in a borosilicate matrix and ascribed to the l=0, l=2, and l=1 modes of a spherical particle. Pump-probe stimulated Raman measurements on the same sample reveal only the symmetric l=0 mode, the frequency of which increases as the laser central energy moves to higher energies. Consistent with the strong dependence of the exciton energy on the particle size, such a behavior is attributed to resonant size-selective excitation of nanocrystallites whose absorption edge coincides with the central energy of the optical pulses. This selectivity, relying on the existence of double-resonant terms in the generation process, is not observed in spontaneous Raman scattering for which the resonances involve a single term.