The effects of different interfacial environments on the optical nonlinearity of nanometer-sized CdO organosol

Abstract

The third-order optical nonlinearity χ(3) of nanometer-sized CdO with different interfacial environments has been measured using the Z-scan technique. The real and imaginary parts of χ(3) at 800 nm have been determined to be: −1.55×10−16 m2/W and 0.91 cm/GW for CdO–CTAB (cetyltrimethyl ammonium bromide) organosol, and −6.97×10−16 m2/W and 8.64 cm/GW for CdO–DBS (dodecylbenzene sulfonate) organosol. Origins of the optical nonlinearity and the effects of the interfacial conditions have been discussed. The optical Stark effect (OSE) and surface trapped states are the possible origins of the observed optical nonlinearity. The possible enhancement of optical nonlinearity of nanoparticles by intentional interfacial modification is suggested.

Spectroscopy of the nonlinear refractive index of colloidal PbSe nanocrystals

“…2͑d͒, we obtain n 2,PbSe values of −6.5 10 −7 cm 2 / W. These are among the highest values reported for colloidal semiconductor quantum dots. 4,5,9,10 The correlation between the absorbance and the nonlinear refractive index spectrum and the observation of refractive index saturation suggest that state filling lies at the origin of the observed nonlinear effects. Combining the pulse duration, intensity at the focus, and repetition rate of the laser with the lifetime of a single exciton ͑0.66 s for 5.4 nm Q-PbSe, determined from the luminescence decay͒, the steady state fraction of nanocrystals containing a single exciton can be calculated.…”

“…Applications of colloidal semiconductor nanocrystals ͑or quantum dots͒ have already been explored in optoelectronic or photovoltaic devices ͑photodetectors, 1 light emitting diodes, 2 and lasers 3 ͒. An additional field of applications may follow from recent studies indicating that quantum dots show strongly enhanced nonlinear optical properties, 4 and behave as saturable absorbers. 5,6 Materials with a large and fast nonlinear refractive index can be used in devices such as Mach-Zehnder interferometers, 7 and absorption saturation is a necessary element in passive modelocked lasers.…”

“…5,6 Materials with a large and fast nonlinear refractive index can be used in devices such as Mach-Zehnder interferometers, 7 and absorption saturation is a necessary element in passive modelocked lasers. 8 Unfortunately, most studies on the nonlinear optical properties of colloidal nanocrystals are performed either at energies well below the first one-photon transition ͑also referred to as the band gap͒ 4,5 or when performed around the band gap, yield results cloaked by thermal effects. 9,10 In this letter, we present the results of a very detailed study on the nonlinear refractive index n 2 of colloidal PbSe quantum dots ͑Q-PbSe͒ in the near-infrared wavelength region of 1200-1750 nm.…”

“…The characteristics of the samples used for the present study are summarized in Table I. After synthesis, the particles were dispersed in CCl 4 . The nonlinear refractive index n 2 and nonlinear absorption ␤ were determined with the Z-scan technique 13 using a tunable femtosecond mode-locked laser operating at an 82 MHz repetition rate and at wavelengths in the ranges of 1200Ϫ1350 and 1540-1750 nm.…”

The non-linear refractive index of colloidal PbSe nanocrystals: Spectroscopy and saturation behaviour

“…Here we not only focus on the efficient generation of light but also on the manipulation of light, taking advantage of unique optical properties of semiconductor quantum dots. Recent studies have already demonstrated that quantum dots show an enhanced nonlinear refractive index [6] and behave as saturable absorbers [7,8]. These effects can be used for instance to achieve all-optical switching [9].…”