This comprehensive review is formatted in a non-standard way: upon the casting of an equation citations will be given for each manuscript which reports it. This is done in the hopes of minimising possible confusion due to the myriad of methods available. These lists are laborious and exhaustive, but likely incomplete. Many works for example are inaccessible due to the era in which they were written (language, USSR; cold war-era), or issues with physical vs digital copies of old texts. Hence, we have only cited those works which we could find either physically or digitally. However, for more information we recommend examining these works where available. It should also be emphasised that in the solid state and quantum dot literature, the term "charge recombination" is used rather than internal conversion. While charge recombination can refer to any method in which recombination occurs, and therefore also includes fluorescence, based on the coupling, we infer the mechanism of internal conversion for charge recombination. Therefore, in this review, we will use internal conversion as our primary terminology.