Afterglow Phosphor Goes Transparent

Recently, transparent afterglow phosphors have attracted increasing interest due to the mitigated self-absorption and the ensuing improved light output, which have inspired many advanced applications, including volumetric display and three-dimensional optical encryption. To date, the most successful afterglow phosphors remain those traditional oxide, nitride, or sulfide powders which are not transparent due to a severe scattering effect. By reduction of the number of interfaces and engineering the refractive index, the scattering effect could be circumvented effectively. To this end, four material systems, including transparent afterglow single crystals, transparent phosphorescent organics, transparent afterglow glass, and luminescent nanocomposites, were reviewed in this Perspective. We started with the discussion of the nontransparency origin. Through a careful inspection of Rayleigh scattering theory, a general solution involving both refractive index and particle size was proposed to reduce the scattering effect. Many representative works on transparent afterglow phosphors were systematically reviewed, where the typical synthesis methods and the advantages and disadvantages of each system were critically presented. In the last part, bottlenecks, prospects, and future development directions based on transparent afterglow phosphors are proposed.