Georgi Nadjakov

Georgi Nadjakov became a corresponding member of the Göttingen Academy of Sciences (1940) in Germany, member of the Bulgarian Academy of Sciences (1945) and member of the Russian Academy of Sciences (1958). Sofia University sent him to specialize in the laboratories of Paul Langevin and Marie Curie in Paris, where he investigated photoelectricity for one year. He experimentally investigated photoconducting properties of Sulphur. He prepared the permanent photoelectret state of matter for the first time and published his paper in 1937 and 1938.He called the electret discovered by Mototaro Eguchi in 1919, thermoelectret and the electret discovered by him in 1937, photoelectret.
His most notable achievement were the photoelectrets. Its practical application led to the invention of the photocopier by Chester Carlson some years later.