Yes Technology have no boundary. We are upgraded with every new technology. The invention of the television was the result of the work by many inventors, scientists and engineers in the late 1800’s and early 1900’s. Many inventors made technological breakthroughs that were used by other inventors to successfully make working television systems. The first working television systems were electromechanical and used a motor-generator. Electronic television systems or all-electronic television systems do not have or use a motor-generator. The first electromechanical television was proposed and patented by Paul Julius Gottlieb Nipkow in 1884. The first Cathode Ray Tube (CRT) was built by Karl Ferdinand Braun in 1897. John Logie Baird was the inventor who built the world’s first working television system in 1925. The world’s first successful color transmission by John Logie Baird in 1928. The first working liquid crystal display (LCD) was built by George H. Heilmeier in 1964. After the LCD it is the time of LED & Plasma age. But now LCD, LED & Plasma are old technologies. The Latest & new technology is OLED (organic light-emitting diode). which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes. Generally, at least one of these electrodes is transparent.
A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over all or part of the molecule. These materials have conductivity levels ranging from insulators to conductors, and therefore are considered organic semiconductors. The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors. The most basic polymer OLEDs consisted of a single organic layer. During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. A current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. This latter process may also be described as the injection of electron holes into the HOMO. Electrostatic forces bring the electrons and the holes towards each other and they recombine forming an exciton, a bound state of the electron and hole. This happens closer to the emissive layer, because in organic semiconductors holes are generally more mobile than electrons. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation whose frequency is in the visible region. The frequency of this radiation depends on the band gap of the material, in this case the difference in energy between the HOMO and LUMO.
As electrons and holes are fermions with half integer spin, an exciton may either be in a singlet state or a triplet state depending on how the spins of the electron and hole have been combined. Statistically three triplet excitons will be formed for each singlet exciton. Decay from triplet states (phosphorescence) is spin forbidden, increasing the timescale of the transition and limiting the internal efficiency of fluorescent devices. Phosphorescent organic light-emitting diodes make use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states, thus obtaining emission from both singlet and triplet states and improving the internal efficiency.
