One- and two-photon-pumped luminescence studies on DAST and UDAST organic dye molecules

Abstract

The Optical studies on chemically synthesized DAST (4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate) and UDAST (containing urea as additive) samples have been carried out in solid and solution phases. Both the solid samples show intense one-photon fluorescence in the 550–850-nm region when pumped with wavelength lower than 550 nm. Solid DAST shows two broad emission bands centered at 589 nm (intense) and 721 nm (weak). Solid UDAST sample also exhibits two bands centered at 618 and 740 nm but opposite pattern in intensity. The emission band at 721 nm was supposed to arise due to the intermolecular charge transfer (ICT) from one chromophore (stilbazolium) to another (tosylate). The effect of urea on the fluorescence emission is discussed. In solution phase both the samples show only single fluorescence band (band width ∼75 nm) at 611 nm peak wavelength. Also, the DAST and UDAST in solid/solution phase show two-photon-pumped (TPP) upconversion emission on 1.06 μm pumping. Further, DAST was doped into a sol–gel-derived glass matrix, and in this glass a new emission band has been observed at 402-nm on 266-nm pump wavelength.