Fluorescence spectroscopy of Rhodamine 6G: Concentration and solvent effects Florian M. Zehentbauer a , Claudia Moretto a , Ryan Stephen a , Thangavel Thevar a , John R. Gilchrist b , Dubravka Pokrajac a , Katherine L. Richard c , Johannes Kiefer a,d,⇑ a School of Engineering, University of Aberdeen, Fraser Noble Building, Aberdeen AB24 3UE, Scotland, United Kingdom b Gilden Photonics, 9 South Avenue, Clydebank Business Park, Clydebank G81 2NR, Scotland, United Kingdom c Magdalen College School, Oxford, United Kingdom d Erlangen Graduate School in Advanced Optical Technologies, University of Erlangen-Nuremberg, 91052 Erlangen, Germany highlights  Both concentration and solvent effects can be utilized for tuning the optical emission of Rhodamine 6G.  Rhodamine 6G fluorescence in aqueous solutions has been studied from highly dilute to high concentration systems.  At low concentration isolated dye molecules are present while aggregates are formed at high concentration. graphical abstract article info Article history: Received 27 June 2013 Received in revised form 11 October 2013 Accepted 17 October 2013 Available online 25 October 2013 Keywords: Rhodamine 6G Rhodamine 590 Alcohol Laser-induced fluorescence Flow visualization Dye laser abstract Rhodamine 6G (R6G), also known as Rhodamine 590, is one of the most frequently used dyes for applica- tion in dye lasers and as a fluorescence tracer, e.g., in the area of environmental hydraulics. Knowing the spectroscopic characteristics of the optical emission is key to obtaining high conversion efficiency and measurement accuracy, respectively. In this work, solvent and concentration effects are studied. A series of eight different organic solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, n- pentanol, acetone, and dimethyl sulfoxide (DMSO)) are investigated at constant dye concentration. Rela- tively small changes of the fluorescence spectrum are observed for the different solvents; the highest fluo- rescence intensity is observed for methanol and lowest for DMSO. The shortest peak wavelength is found in methanol (568 nm) and the longest in DMSO (579 nm). Concentration effects in aqueous R6G solutions are studied over the full concentration range from the solubility limit to highly dilute states. Changing the dye concentration provides tunability between 550 nm in the dilute case and 620 nm at high concen- tration, at which point the fluorescence spectrum indicates the formation of R6G aggregates. Ó 2013 Elsevier B.V. All rights reserved. Introduction Over the past five decades, fluorescent organic dyes have found a variety of applications in the field of optical technology. Two major areas are their use in dye lasers and as tracers for laser-in- duced fluorescence (LIF). The first laser action using organic dyes was reported in 1966 [1]. Since then dye laser physics and related technology has undergone significant development on a par with the rapid advancements in laser science. A major advantage of a dye laser is its broad spectral emission characteristics that allow wavelength tuning and generation of mode-locked short pulses. In addition, dye lasers offer simplicity and versatility of operation, 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.062 ⇑ Corresponding author at: School of Engineering, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom. E-mail address: j.kiefer@abdn.ac.uk (J. Kiefer). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 147–151 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa