Russian physicists developed a technique for creating new planar metal-organic structures, which can serve as a basis for producing submicron electroluminescent light sources with adjustable emission spectrum.

Finding alternatives to all existing light sources is a very important task of the current century. Lets be honest, incandescent bulbs are outdated. As for luminescent lamps, they are widely used, but sophisticated in production and difficult to utilize. That it why, researchers and engineers actively search for new types of light sources, based on semiconductor light-emitting diodes (LEDs), for instance, or on organic light-emitting diodes (OLEDs). Russian and Ukrainian physicists started working with electroluminescent metal-organic structures, which were unfairly forgotten.

Planar structures, which are light sources, are made the following way. Firstly, gold film is thermally sprayed into a 30 micron gap between two film electrodes on a glass substrate. Thermal spraying takes place in ultra-high vacuum under pressure of about 10 torr (about 10 millimeters of mercury). Gold film consists of little isles, and is called metal island film, which is known quite well. Russian scientists sprayed organic layer over metal film, thus making light spectrum depend on both metal and organic components. Changing organic compound means changing spectrum parameters. Thus, researchers made submicron light sources with adjustable emission.

 

 

Emission spectra of incandescent bulbs and luminescent lamps turns out to be close to natural daylight, coming form the Sun. Radiation of many new light sources is often far from being so friendly to human beings, and this is one of the main problems on their triumphant march to the market. Researchers need to create alight source, which emission spectrum won’t contain unwanted radiation components, and most energy is concentrated in visible light range, to which human eye is used. Electroluminescence of structures, created by Russian and Ukrainian physicists, provides everything to control emission spectrum of a light source, in other words, we can have new sources of “natural” light.

Organic components of mentioned structures included Alq3 (Tris(8- hydroxyquinolinato) aluminium) and β-diketonates of rare earth elements: Eu(DBM)3bath, Eu(DBM)3phen, Eu(DBM)3*2H2O, Tb(thd)3. Alq3 is a standard electroluminescent material, which was the basis for first ever organic LED in 1986. Alq3 was used as a positive control in the experiment. Successful tests allowed researchers to try organic complexes of europium and terbium. These rare earths were chosen for characteristic bands in emission spectra, which make them easily recognizable. All this allows physicists to find out a mechanism of electric luminescence in these compounds.

As a result of described research, scientists created planar light-emitting structures, based upon gold island films and organic complexes of rare earth metals – europium (Eu) and terbium (Tb). Physicists also revealed the mechanism of electroluminescence of a structure, in which organic component dominated. Mentioned structures are light sources, emitting red (Eu complexes) and green (Tb complexes) light.

Source: Institute of Physics

Kizilova Anna