Phonon-Mediated Nonradiative Relaxation in Ln³⁺-Doped Luminescent Nanocrystals

Unsatisfactory photoluminescence efficiency of Ln3+-doped nanocrystals severely restricts their practical application, which has been frequently correlated to the active phonon mediation in the system. Although the phonon-mediated nonradiative relaxation of Ln3+ has been mostly explained by the "energy gap law", a growing body of observational anomalies raises questions about the general applicability and validity of this phonon frequency-orientated model. For that reason, an improved understanding, questioning commonly accepted views, is needed. Herein the discussion relevant to this topic is reviewed, stressing that for phonon-mediated nonradiative relaxation in Ln3+-doped nanocrystals not only a variety of effects associated with the particle surface but also impacts arising from the nanocrystal interior need to be considered. A clear awareness of these different aspects allows comprehending the delicate electron-lattice interactions in these systems, which is helpful in improving the performance of Ln3+-doped luminescent nanocrystals.