Nanoplasmonics and surface enhanced spectroscopy

Photonics of a merocyanine dye near the surface of plasmon silver and gold nanoparticles
Aimukhanov A. K., Ibrayev N. Kh., Ishchenko A.A.
Institute of Molecular Nanophotonics, Buketov KarSU, Universitetskaya str. 28, Karaganda 100028, Kazakhstan.
E-mail: niazibrayev@mail.ru, a_k_aitbek@mail.ru

Institute of Organic Chemistry, Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanskaya str. 5, 02660 Kiev-94, Ukraine 
E-mail: alexish@i.com.ua

The effect of the plasmon of silver and gold nanoparticles (NPs) on the absorption and fluorescence properties of the merocyanine dye. NPs of silver and gold were obtained by laser ablation of targets in ethyl alcohol. The average size of silver nanoparticles is 27 nm, and gold 95 nm. The concentration of silver NPs in the ethyl alcohol was CAg = 2.4•10-11 M, and gold NPs CAu = 1.3•10-12 M. The absorption spectra of nanoparticles well overlap with the absorption and fluorescence spectra of the dye and indicates that plasmon resonance conditions. The dye absorption band at a concentration of 10-5 M has a maximum at a wavelength λmax = 590 nm and a half-width of 25 nm. The dye fluorescence has a maximum at the wavelength λmax = 615 nm and a half-width of the band 28 nm.
When a silver NPs at the concentration of 0.89•10-12 M is added to the dye solution, the optical density at the absorption maximum increases by 1.2 times.
At the same time, it was found that the presence of a gold NPs in the solution does not affect the optical density in the absorption spectrum of the dye.
When the silver NPs is added to the solution, the intensity of the dye fluorescence increases up to the concentration of CAg = 0.89•10-12 M, and a further increase silver NPs leads to quenching of the fluorescence.The intensity of fluorescence of the dye in the presence of gold nanoparticles is quenched.
The decrease of fluorescence occurs by exponentially with τFl = 0.6 ns. When silver is added to the solution, the decrease of fluorescence does not change, and when gold is added to the solution, the decrease of fluorescence is shortened
The quantum yield of fluorescence was Φf = 0.41. When silver NPs is added to the solution, the quantum yield of the dye does not change. In the case of gold NPs, the quantum yield is decreases to 0.31.