1. Light emission – a Light-emitting diode is something that we are very familiar with, more commonly referred to as an “LED.” LED’s are used in many applications and are becoming more and more popular due to their efficiency and longevity. “A typical LED for lighting can deliver 50–60 lumens per watt, which is approximately five times greater efficiency than a standard incandescent bulb (Thomas L Floyd).” When the LED is in forward bias, electrons that combine with holes in p-type materials coming from the n-type materials. Once recombination takes place an energy is released in the form of photons. A semiconductive material is what allows the photons to be projected as visible light.
2. A phototransistor is similar to a Bipolar Junction Transistor (BJT) except the base currents are generated from two different sources. The base current in a BJT is produced by a voltage source while the phototransistors come from a light source. Phototransistors can be found in punch card readers, counting systems, and even in light controlling/detection systems. The phototransistor operates dependent on the level of radiation detected in form of light, and not just any light source but only those within a certain range of wavelengths.
Floyd, T. L. (2017). Electronic Devices (Conventional Current Version) (10th ed.). Pearson Education (US). https://ecpi.vitalsource.com/books/9780134414553
Roshni Y (2023) What is a Phototransistor? Definition, Construction, Working, Characteristics Curve of Phototransistor – Electronics Desk