Chapter 8: Blue Light Chargeable Persistent Phosphors

Abstract

Persistent phosphors are materials that show continuous luminescence for a long duration, from several minutes to a few hours after ceasing the excitation light. They have been used in luminous paints in indoor and outdoor environments, for emergency signs, watch dials, etc. In this chapter, the history of persistent phosphors and the persistent luminescence mechanism are described, and our new persistent phosphors are introduced. In 2013, a blue light chargeable persistent phosphor, Y₃Al₅₋ₓGaₓO₁₂:Ce³⁺-Cr³⁺, was successfully developed by our research group on the basis of material design for persistent phosphors; this has also been explained in the text. For the charging process, the relative energy location between the excited Ce³⁺:5d level and the bottom of the conduction band was controlled by bandgap engineering. In addition, Cr ions were co-doped into the bandgap engineered Y₃Al₅₋ₓGaₓO₁₂:Ce³⁺ phosphor to form numerous electron traps. The detailed properties of Y₃Al₅₋ₓGaₓO₁₂:Ce³⁺-Cr³⁺ for the charging and de-charging processes were analyzed by thermoluminescence measurements. Tuning of the persistent luminescence color is also discussed.