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Artificial White Light is Eye-friendly
Oct 2010
WARSAW, Oct. 8, 2010 — A newly discovered class of organic substances that emit white light with a continuous spectrum is providing experimental evidence that only single component luminophore will be necessary to construct eye-friendly light sources and displays.

The discovery, made by scientists from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Faculty of Chemistry of the University of Warsaw, has shown that eliminating the unpleasant side effects that artificial lights can have on the eyes can be achieved.

White fluorescence observed by scientists from the Institute of Physical Chemistry of the PAS in CVL molecules continuously covering practically the entire range of visible light. The discovery shows that in future it will be possible to create non-thermal light sources giving the impression of natural white color, based on single component luminophore. (Image: IPC PAS, Grzegorz Krzyzewski)

"We have discovered a class of organic molecules emitting white light with continuous spectrum covering almost the entire visible range,” said Dr. Jerzy Karpiuk from the IPC PAS who heads the research team. It is also important that the emission of the white light was obtained from one chemical compound with a very simple structure.

White is a special color which is created as a result of mixing of light waves of all lengths from the visual range, i.e. from approx. 420 to approx. 730 nm. The white color of fluorescent lamps and similar artificial sources is created by the mixture of three colors only: red, green and blue, which come mainly from the non-continuous emissions of various inorganic (halophosphate or triphosphate) luminophores. The light obtained in this way is devoid of many color components and it is this effect that is responsible for the unpleasant visual sensations. In addition, the need to use several substances lowers the energetic efficiency of light sources and complicates their manufacturing technology.

The research team composed Karpiuk and Ewelina Karolak, also from IPC PAS; and Jacek Nowacki, faculty member at the Chemistry of the University of Warsaw; observed white light emission continuously covering virtually the entire visible range. Its source is crystal violet lactone (CVL), a substance produced in mass quantities and commonly used in copy paper as the so-called dye precursor.

A CVL molecule has two fluorophores embedded in its structure and responsible for the emission of light: one for blue and the other one for orange. The contribution of each of them to CVL’s dual fluorescence heavily depends on the environment of the molecule which modifies the energetics of their excited states.

"By properly adjusting the molecule’s surrounding, it is possible to control the parameters of the emission spectrum, and consequently, to change the color or shade of the white light obtained," said Karolak.

"The deeper significance of our research lies in the discovery that white fluorescence is a general property of CVL type molecules. The dependence of excited state energetics on molecular structure allows to predict the width, shape and other parameters of the dual fluorescence spectrum, and so enables the engineering and customized design of white fluorophores," he said.

It turns out that even very small molecules can emit continuous white light. This fact opens up a new perspective for the construction of innovative eye-friendly light sources.

The emission of white light by molecular structures as simple as CVL is highly desired and wanted phenomenon, mainly because of its potential use in organic light-emitting diodes. However, it is still a long way before it can be used in practice because crystal violate lactone emits light of low intensity and CVL-based light sources would not be efficient enough to be manufactured on a mass scale.

"However, the most important thing is that we managed to show that a certain concept works in practice. Now we are sure that it is only a matter of time before light sources recreating natural white light will be constructed," Karpiuk said. 

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white light
Light perceived as achromatic, that is, without hue.
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