Use of Luminescent Conjugated Polymers

The use of conjugated light emitting polymers in the construction and commercialisation of organic LEDs is described in the section 3.8.6 on electroluminescence phenomena of Chapter 3. The rapid expansion of the development work on LEDs has inevitably led to the examination of luminescent conjugated polymers as materials for constructing laser diodes. 

The lowest excited states in luminescent conjugated polymers are very similar to the dyes used in dye lasers (Chapter 3, section 3.5.3). Therefore the conjugated polymers can be used to achieve population inversion by optical pumping as with the laser dyes. 

Examples of the optical pumping of solutions of luminescent conjugated polymers include laser action at 596 nm of poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) using excitation with 6 ns Nd YAG third harmonic pulses (354.7 nm). ° Tuning of hexane solutions of the co-polymer poly(2,2, 5,5 -tetraoctyl-p-terphenyl-4,4 -xylene-vinylene-p-phenylenevinylene) (TOP-PPV) was possible between 414 and 456 mn, similar to the classical coumarin laser dyes.  

An important difference between luminescent conjugated polymers and laser dyes is that the former still exhibit strong optical gain in the solid state. This property means that luminescent conjugated polymers can be used to produce stimulated emission in thin films of these materials. 

The first report of lasing action (600 nm) in the solid state involved the use of MEH-PPV as a blend with dispersed nanoparticulate TiOj, which acted as scatterers to achieve lasing. This was quickly followed by the first non-blended, microcavity laser, using PPV, that could support high current densities. To date a whole range of 

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