As a PhD student, I took a course in inorganic photochemistry. One of the first soundbites – “photons are expensive” – came with my parents’ endless admonitions to turn off the lights, especially when visiting my grandmother in Italy.
As a species, we are addicted to light. The use of fire was the means by which people increased their food security, but flickering fire lights also lengthened the day and strengthened social bonds. The lighting also had a profound intellectual impact as it made reading and writing possible indoors and at night. However, it took 5000 years to move from using a simple wick and some oil to something lighter.
The main reason for this was the rise of chemistry. The 18th century ended with the idea that combustion required both fuel and oxygen. This idea was triumphantly used by François-Pierre-Amédée Argand, whose idea of a chimney around a large wick soaked in whale oil significantly increased the airflow and the temperature of the flame and increased its brightness. Combustion lamps of this kind in combination with coal gas would reach their peak with Karl Auer’s invention of the incandescent lamp jacket around 1889. But the writing on the wall was for flames.
Humphry Davy didn’t just electrolyze salts. He also invented the carbon arc, the dazzling glare of which was powered by his “battery” of voltaic piles. This amazing development was not a flash in the pan, and arc lamps remained the brightest sources of light that were gradually enclosed in lightbulbs. The air inside has been replaced by inert gases – especially xenon with its bright bluish shimmer.
But the real money was in incandescent lamps. Davy was probably the first to incandescent a platinum wire – an observation that would eventually spark a huge industry. While surprisingly inefficient and rarely converts more than 3% of drive power to light, the simplicity of the technology led it to spread to dominate the lighting ecosystem.
The only competitor was initially fluorescence, which was first correctly identified by Gabriel Stokes. Glowing gases in discharge tubes were spectacular sources of light. In 1859 Antoine Becquerel (the father of the Nobel Prize winner) had the idea of coating the inside of a Geissler tube with a fluorescent material (a phosphor). Although the color matching would affect the discharge tube lighting and limit it to industrial and business environments for a long time, the efficiencies could be spectacular. The sodium lamp by Frans Michel Penning converted 60% of the power into light.
But fluorescent lamps were eventually replaced by another highly efficient technology from all but the most specialized applications: the light emitting diode or LED. In 1907, an English inventor and engineer, Henry Round, who developed radio for Guglielmo Marconi, made a strange observation: some of the crystalline silicon carbide whiskers he used in his radio detector circuit gave off a special glow. Round found that applying voltage to these whiskers often resulted in the emission of random colors of light. He speculated that this might be a new phenomenon. His work was forgotten.
Light, radio, action!
A brilliant young Russian scientist, Oleg Losev, rediscovered the phenomenon in the 1920s. As a technician with few formal qualifications, Losev worked independently on diodes with zinc oxide-silicon carbide junctions. With these he designed radios based on the same subtractive superposition principle that was later used to process NMR signals. These “Kristadin” sets were the first “solid state” radios, but they were built without transistors. Exhibited across Europe in the 1930s, they caused a minor sensation, but did not succeed.
While studying the behavior of these diodes in 1923, Losev observed a greenish glow near the steel contact. When he reversed the voltage, the glow disappeared – although the current was greater than with the other polarity. Losev meticulously recorded the spectra of light and studied its temperature dependence, a work that anticipated the much later discovery of the semiconductor laser. Using photomicrographs, he found that the light came from a thin layer near the electrode and could distinguish between two different types of luminescence. Long before the band theory, he worked with the idea of considering holes as possible charge carriers and interpreted his data in the opposite direction as a photoelectric effect. He even wrote to Einstein for advice. His work was decades ahead of its time. The fact that all of his patents and publications bear only his name suggests that his colleagues and supervisors were aware of his extraordinary talents.
After five years at a university of applied sciences, Losev received the equivalent of a doctorate in 1938 and was allowed to return to the research laboratory. He worked in Leningrad during World War II and, against the advice of his boss, stayed in his laboratory even when German troops besieged the city. He is said to have starved to death in 1942 and his job was almost forgotten.
It was not until the 1960s that solid-state luminescence really began to increase. I first saw LEDs in the little red digits on the Texas Instruments calculator my father bought. Their size and brightness have steadily increased, as has control over their color. Although mercury lamps are still used in our laboratories for experiments with ultraviolet photochemistry, gallium nitride LEDs are now much cheaper and more reliable to operate. In conjunction with fluorescent coatings, their visibly emitting cousins now dominate both household and commercial lighting. Poor, starving Losev might be amazed at his legacy. And maybe he would come up with something to make photons even cheaper.