Scientists of the Zelinsky Institute have developed new improved organic light-emitting diodes with candles light characteristics
When creating artificial lighting, light-emitting diodes began to actively displace incandescent lamps only a couple of decades ago and at the moment they continue to confidently dominate the market. However, the light range of LED and gas-discharge light sources is highly enriched in blue radiation, which adversely affects many materials, causing their accelerated destruction, can harm entire ecosystems if such light sources are used for outdoor lighting, and also pose a threat to the human eye and can cause physiological disturbances in the body due to a noticeable decrease in the concentration of melatonin. The spectral composition of the light of modern commercial LEDs differs sharply from that characteristic of sources based on a physically heated body (flame, incandescent lamps or sunlight). Despite the fact that they can provide a visually warm yellow tint of light (color temperature 2400 K and even lower), in fact, LEDs are a combination of blue and ultraviolet light, which is emitted by a semiconductor crystal, and a crystal-supported special luminophore of yellow-orange glow with significant dips in the area of green and red radiation. Therefore, the creation of safe LED devices with light characteristics similar to those of a candle flame (low color temperature with a continuous spectrum of radiation) is one of the important scientific problems of practical importance.
Earlier, the researchers of the laboratory № 31 of the Zelinsky Institute together with scientists from the Lebedev Physical Institute and Mendeleev University of Chemical Technology of Russia developed a new light source that practically does not have harmful radiation in the blue region of the spectrum due to an innovative design and a combination of new specially synthesized luminophores. The color characteristics of its radiation are similar to the light characteristics of the flame of ordinary candles. However, this device had relatively low brightness values in comparison with other existing organic light-emitting diodes (maximum brightness 1831 Cd / m2 for one of the structures).
In continuation of the work on improving the physiologically safe LED based on a hybrid of organic and organometallic emitting materials, a new more efficient organic light-emitting diode with the light characteristics of candles was developed (candle light-style organic light emitting diode, CLS OLED), which does not contain blue and ultraviolet parts of the spectrum and has a low color temperature. New organic dyes specially synthesized by in the Laboratory № 31 of ZIOC were used as one of the layers. Replacing the pyridine ring with a benzene one in the internal acceptor increased the LED brightness more than three times up to 6256 cd / m2, while the color temperature remained at the record level (1880-1990 K).
The developed devices can be used as light sources for office, household, and public spaces, but they will be especially useful as home lamps to facilitate falling asleep and create comfortable soft lighting. The relatively simple technology for manufacturing these diodes and inexpensive raw materials will allow in the future development of light sources in the form of flat panels of sufficient area with adjustable brightness and some possibilities of adjusting the glow color only by changing the parameters of the supply voltage.
Source:
V. M. Korshunov, T. N. Chmovzh, I. S. Golovanov, E. A. Knyazeva, L. V. Mikhalchenko, R. S. Saifutyarov, I. C. Avetisov, J. D. Woollins, I. V. Taydakov, O. A. Rakitin Candle light-style OLEDs with benzochalcogenadiazoles cores Dyes Pigm., 2021, 185, 108917. DOI: 10.1016/j.dyepig.2020.108917.