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. - Highlights: • The SrAl₂O₄: Eu²⁺, Cr³⁺, Dy³⁺ phosphors are prepared by sol-gel-combustion method. • Efficient energy transfer from excited Eu²⁺ ions to Cr³⁺ ions is realized. • The energy transfer is due to the overlap of energy levels of Eu²⁺ and Cr³⁺ ions. • Persistent luminescence in tissue transparency window is realized. • The optimum doping concentration of the emission centers is studied