Persistent luminescence of SrAl2O4: Eu2+, Dy3+, Cr3+ phosphors in the tissue transparency window

We report on the persistent luminescence of SrAl2O4: Eu2+, Cr3+ phosphor centered at 760 nm. The phosphor was prepared by sol-gel-combustion method. Persistent luminescence from Cr3+ lasted for hundreds of seconds, comparable to the long afterglow from Eu2+ ions in the visible region based on the continuous energy transfer from Eu2+ ions to Cr3+ ions. The introduction of Dy3+ ions into the phosphor further prolonged the afterglow time of Eu2+ and Cr3+ ions through the depth control of the charge traps. The optimum doping concentrations for Eu2+, Cr3+ and Dy3+ were 1%, 2% and 1.5%, respectively.