Applied Physics

How Two Blue Lights Make a White Light

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Science  10 Aug 2001:
Vol. 293, Issue 5532, pp. 1015
DOI: 10.1126/science.293.5532.1015b

White light can be formed by mixing colors from different parts of the visible spectrum (red, green, and blue), but Thompson et al. now show that white photoluminescence can be generated from pairs of organic materials (which individually emit blue light) when excited with an ultraviolet laser. The redshifted emission spectrum was not caused by the formation of new chemical species, as determined by absorbance spectroscopy of thin spin-coated films. Instead, the authors show that a complex is formed from the excited state of one of the molecules [2,5-bis(trimethylsilyl thiophene)-1,1-dioxide or STO] and the ground state of the other [N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine or TPD]. This “exciplex” lies between the excited and ground states and has an energy gap that is lower than those of the component materials; this broadens the emission to longer wavelengths, which provides the additional colors needed to make white light. The formation of such exciplexes is not limited either to polymer-polymer blends or by material interfaces. Thus, inexpensive, organic, white light-emitting diodes might be obtained by appropriate blending of blue-emitting materials. — MSL

Appl. Phys. Lett.79, 560 (2001).

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