Abstract
The smart utilization of photons is paid global attention from the viewpoint of renewable energy and information technology. However, it is still impossible to store photons as batteries and condensers do for electrons. All the present technologies utilize (the energy of) photons in situ, such as solar panels, or in spontaneous relaxation processes, such as photoluminescence. If we can store the energy of photons over an arbitrary period and utilize them on demand, not only we will make an innovative progress in energy management, but we will also be able to replace a part of electrons by photons in the information technology for more efficient performance. In this article, we review a prototype of such a material including the current status of related research as well as where we are heading for.
Highlights
In this review, we will focus on the photoexcited states and properties that persist even after irradiation is ceased
Based on photon energy storage (PES), we will make innovative progress in energy management, but we will be able to replace a part of electrons by photons in the information technology for more efficient performance
They slowly release stored energy as light during a few minutes to several days with a possibly different mechanism from that of phosphorescence, as the temperature-dependence of relaxation time and the emission spectra are qualitatively different between persistent luminescence (PersL) and phosphorescence even for the same material capable of both types of luminescence under the same wavelength of photoexcitation [8]
Summary
Photoexcited states and subsequent relaxation processes, which are generally quick and complicated series, often produce otherwise impossible unique and interesting phenomena. The well-known phenomena of photoluminescence are fluorescence and phosphorescence (Figure 1) [4] Both include radiative decay processes, during which molecules give off photons after receiving the excitation energies under irradiation. They slowly release stored energy as light during a few minutes to several days with a possibly different mechanism from that of phosphorescence, as the temperature-dependence of relaxation time and the emission spectra are qualitatively different between PersL and phosphorescence even for the same material capable of both types of luminescence under the same wavelength of photoexcitation [8]. In OLPL, the materials slowly release stored exciton energy as light, having a thousand times longer life of emission (over 1 h in some cases) after cessation of photoexcitation In this slow emission, an intermediate state plays an indispensable role. We shall not discuss them here, since they are less relevant to the following discussion
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