Introduction

SrAl2O4:Eu2þ, Dy3þ crystals are among the materials that exhibit the most pronounced phosphorescence that is appealing for alternative lighting technologies that are independent, rechargeable, and energy efficient. Here, phosphorescence refers to the delayed emission of light around room temperatures (RTs) after excitation of the crystals by blue or UV light. The crystal structure of SrAl2O4 is monoclinic. The unit cell comprises of four formula units where together they form eight AlO4 tetrahedra that are linked through shared oxygen corners with four Sr2+ ions located among the tetrahedra. Dopant ions can be introduced to the host matrix SrAl2O4 where they occupy the Sr2+ sites. By altering the chemical composition, stoichiometry, and dopant ions of the system, it is possible to tune the color of luminescence, the temperatures at which the glow is optimal, the intensity and duration of afterglow, and more.

Result and Discussion

Here, we demonstrate the utilization of SrAl2O4:Eu2þ, Dy3þ crystals as light-energy storage by carrying out the following simple procedure. First, crystals are photocharged using blue light (400nm) at RTs. Then, the crystals are rapidly quenched to liquid nitrogen bath to 80 K temperatures. As shown the first picture (see gallery), this results in an instant suppression of the light emission. What is remarkable is that even after more than 6 h (in this test) being kept at low temperatures and in the dark, that the crystals re-glow when they are brought back to RTs.

Conclusion

We have demonstrated and evaluated the viability of SrAl2O4:Eu2þ, Dy3þ as lightenergy storage. The rules for using the crystal as light-energy storage is simple: (1) charging is best done at Tcharge; (2) keep the crystal at low temperatures,  80 K, to suppress the trap activities; (3) use the crystals at or below Tmax. In our case, the absorbed light-energy can be stored at least for up to 6 h. Based on the review of various models, it remains a possibility that the suppression of trap activities at trapping centers are directly infuenced by the charge transport behavior of the host matrix. If direct linkage between the charge transport and trap activities is proven to be true, this could open up a new opportunity to improve the switching mechanism to become that of a field-effect-transistor. So instead of lowering/increasing the temperature, switching can be done at RTs via electric field gating. Admittedly, more work is required to verify this possibility.