SHORT NOTE Tunable light emission using crystalline carbon dots Jancy John 1,2 • Raji Mary Mathew 2 • Titu Thomas 2 • Rani Abraham 3 • I. Rejeena 4 • R. Jayakrishnan 2 • Francis Chacko 5 • Vinoy Thomas 2 Received: 16 December 2017 / Accepted: 24 April 2019 Ó The Optical Society of India 2019 Abstract Carbon quantum dots (CQDs) with an approxi- mate size of 8 nm were prepared by a simple and cost- effective green technique—pyrolysis of cotton. Synthe- sized CQDs exhibit broad fluorescence covering almost blue and green light wavelengths. They show low cyto- toxicity and good photostability. A simple mixing of rho- damine 6G chloride with highly fluorescent carbon dots in water led to aggregation of dye molecules on carbon dot surface. Controlling the emission of free rhodamine 6G dye with that of the resultant carbon dot-aggregated rhodamine 6G composite resulted in efficient white light emission with the CIE coordinate (0.305, 0.313). Suitable mixture of blue-light-emitting CQD in aqueous solution and rho- damine 6G dye can potentially be applied for tunable white light emission. Graphical abstract Keywords Carbon quantum dots Á Optical materials Á Tunable light emission Introduction Owing to the increasing demand for white light sources in various fields such as lighting and displays, exploration of efficient and cost-effective white-light-emitting materials has dominated the lightning research. White-light-emitting diodes (WLEDs) are promising light sources due to its long life time, compact size and low power consumption [1]. Fluorescent carbon-based materials have received increas- ing attention in recent years due to exceptional advantages such as high optical absorptivity, chemical stability, bio- compatibility and low toxicity [1–8]. These materials mainly include carbon dots (CDs), nanodiamonds, carbon nanotubes, fullerene and fluorescent graphene [2, 4]. The prominent properties of fluorescent carbon-based materials differentiate them from traditional fluorescent materials & Vinoy Thomas vinoythoma@gmail.com 1 Department of Physics, Mar Ivanios College, Trivandrum, India 2 Department of Physics, Christian College, Chengannur 689122, India 3 Department of Chemistry, Christian College, Chengannur 689122, India 4 Department of Physics, MSM College, Kayamkulam, India 5 Department of Chemistry, St Gregorios College, Kottarakara, India 123 J Opt https://doi.org/10.1007/s12596-019-00529-x