Formation of plasmon-exciton nanostructures based on quantum dots and metal nanoparticles with a nonlinear optical response

Abstract

The establishment of the conditions for the formation of nanostructures with plasmon-exciton interaction based onquantum dots and plasmonic nanoparticles that provide unique nonlinear optical properties is an urgent task. The study demonstrates the formation of plasmon-exciton nanostructures based on hydrophilic colloidal Zn0.5Cd0.5S, Ag2S quantum dots and metal nanoparticles. Transmission electron microscopy and optical absorption and luminescence spectroscopy were used to substantiate the formation of plasmon-exciton hybrid nanostructures. The phase composition of the studied samples was determined by X-ray diffraction. The results obtained using ARLX’TRA diffractometer (Switzerland) indicated a cubic crystal structure (F43m) of synthesised Zn0.5Cd0.5S quantum dots and monoclinic (P21/C) crystal lattice of Ag2S. Transmission electron microscopy revealed that plasmonic nanoparticles are adsorption centres for quantum dots. The average sizes of the studied samples were determined: colloidal Ag2S quantum dots (2.6 nm), Zn0.5Cd0.5S(2.0 nm) and metal nanoparticles: silvernanospheres (10 nm) and gold nanorods (4x25 nm). The transformation of the extinction spectra of the light and the luminescence quenching of quantum dots have been established in mixtures of quantum dots and plasmonic nanoparticles. The nonlinear optical parameters of the studied samples were determined using the Z-scanning method at wavelengths of 355 and 532 nm in the field of nanosecond laser pulses. The conditions for the formation of hybrid nanostructures that provide an increase of the coefficient of nonlinear absorption of laser pulses (355 and 532 nm) up to 9 times with a duration of 10 ns due to the reverse saturable absorption occurring due to cascade two-quantum transitions in the intrinsic and local states of colloidal quantum dots and the suppression of nonlinear refraction, were determined. The observed changes were explained by the manifestation of the Purcell effect on the states of quantum dots in the presence of nanoresonators (gold nanorods and silver nanospheres). The results of these studies create new opportunities for the development of original systems for controlling the intensity of laser radiation, as well as quantum sensors of a new generation