Imidazolium based ionic liquids as novel benign media for liquid-dye laser systems

Room temperature ionic liquids (RTILs) have emerged as nature-friendly media suitable for various applications. In this work, Optical absorption, fluorescence behavior and fluorescence lifetime of three rigorously purified imidazolium ionic liquids, 1-butyl-3-methylimidazolium chloride (BMIM Cl), 1-Butyl-3-methylimidazolium tetrachloroaluminate (BMIM AlCl4), 1-Butyl-3-methylimidazolium tetrafluoro-borate (BMIM BF4) are studied in the neat condition and with two types of laser dyes (PM-597, Fluorescein). The absorption spectra for this dyes in all the ionic liquid solvents investigated looked very similar while the PL emission spectra differed markedly depending on the type of ionic liquid. In pure imidazolium ionic liquids, non-negligible absorption in the UV region with a long tail extending into the visible region is the main feature of the absorption. The emission behavior of neat ionic liquids is found to be strongly dependent on the excitation wavelength. That ion association gives rise to the long absorption tail and shifting fluorescence maximum. While the emission behavior of dye dissolved in ionic liquids independent on the excitation wavelength. Finally, we discuss the suitability of the imidazolium ionic liquids in optical studies taking into consideration their absorption and fluorescence behavior.