“This or that” – light emission from hybrid organic–inorganic vs. coordination Cu(i) halides

In recent years, multiple new families of ultra-high efficiency light emitting Cu(I) halides have been developed for various optical applications. Among the light emitting Cu(I) halides, two distinct materials classes can be recognized, hybrid organic–inorganic Cu(I) halides featuring structurally separated organic cations and Cu(I) halide anions, and coordination Cu(I) halides containing organic ligands attached to Cu(I) centers. These two materials classes have been developed in parallel, and each research field has its own set of terminologies, which has caused confusion regarding similarities and differences between them. In this review, syntheses, crystal and electronic structures, optical properties, and photoemission mechanisms of these two distinct materials classes are compared. This work is concluded with a brief review of exciting potential practical applications of both hybrid organic–inorganic and coordination Cu(I) halides.