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Non-radiative recombination in optoelectronics and phosphors is an unwanted process, lowering the light generation efficiency and increasing heat losses.
Shockley–Read–Hall (SRH) process
The electron in transition between bands passes through a new energy state created within the band gap by an impurity in the crystal lattice. The impurity state can absorb differences in momentum between the carriers, and so this process is the dominant generation and recombination process in silicon and other indirect bandgap materials. It can also dominate in direct bandgap materials under conditions of very low carrier densities (very low level injection). The energy is exchanged in the form of lattice vibration, or a phonon exchanging thermal energy with the material.
Various impurities and dislocations create energy levels within the band gap corresponding to neither donor nor acceptor levels, forming deep-level traps. Non-radiative recombination occurs primarily at such sites.