Abstract
A mixture of extracts from two common vegetables, red pomegranate and turmeric, when photoexcited at 380 nm, produced almost pure white light emission (WLE) with Commission Internationale d’Eclairage (CIE) chromaticity index (0.35, 0.33) in acidic ethanol. It was also possible to obtain WLE in polyvinyl alcohol film (0.32, 0.25), and in gelatin gel (0.26, 0.33) using the same extract mixture. The colour temperature of the WLE was conveniently tunable by simply adjusting the concentrations of the component emitters. The primary emitting pigments responsible for contributing to WLE were polyphenols and anthocyanins from pomegranate, and curcumin from turmeric. It was observed that a cascade of Forster resonance energy transfer involving polyphenolics, curcumin and anthocyanins played a crucial role in obtaining a CIE index close to pure white light. The optimized methods of extraction of the two primary emitting pigments from their corresponding plant sources are simple, cheap and fairly green.
Highlights
Since the amount of emitting natural dyes can change from source to source, the effective concentration of the dyes can be expressed in terms of molarity calculated with this molar extinction coefficient
We have generated white light emission from natural dyes extracted in our laboratory using a green and simple procedure
The optimized mixture of two suitably chosen plant extracts using acidic ethanol, aided by a Forster resonance energy transfer (FRET) cascade from polyphenolics to curcumin to anthocyanins, generates almost pure white light, with Commission Internationale d’Eclairage (CIE) values of (0.35, 0.33) in solution, (0.26, 0.33) in gelatin gel and (0.33, 0.25) in polyvinyl alcohol (PVA) film
Summary
In order to achieve facile tuning of CIE index as well as the colour temperature of interest, we followed a strategy in choosing two vegetable extracts containing emitting dyes such that they emit in blue-violet, green and orange regions of visible spectrum. For this purpose, several trials with blue, green and red emitting natural dyes[30] eventually converged on to two available vegetable extracts, red pomegranate (Pom) seed juice and turmeric (Tur) extract. We have adopted a variant of a method reported by Hamidreza et al.[37], the details of which are given in the section on Materials and Methods
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