Introduction to the basic properties of luminescent materials

Climate change affects people’s lives by altering temperature, water supply, and rainfall and by influencing the frequency of natural disasters. Researchers are actively looking for alternative energy sources that do not emit carbon dioxide. White light-emitting diodes (WLEDs) have been considered one of the most promising next-generation lighting technologies because they significantly reduce global power requirements and the use of fossil fuels. WLEDs have attracted considerable attention because of their significant luminous efficiency, low power consumption, reliability, and environmental friendliness. This chapter discusses the fundamental principles and optical properties of phosphors and quantum dots (QDs) for light-emitting diodes (LEDs). The discussions are mainly focused on the luminescent mechanisms, phosphor and QD components, and the corresponding effects on their optical properties and prospect. We also tackle a number of concepts involved in the nephelauxetic effect, crystal field splitting, energy transfer, thermal effect, and quantum confinement effect, which leads to luminescence. Illustrative examples from luminescent materials applied in lighting are used. Phosphors for ultraviolet (UV) LEDs and blue LEDs are treated separately because the processes leading to excitation, emission, color, bandwidth, and thermal stability are comparable with each other in fluorescent lamps. The production of semiconducting QDs will be discussed with the concept of “the separation of nucleation and growth." The exploration of QD-emission colors emphasizes the core material and nanocrystal size for tuning from near-UV to near-infrared spectra.