Color tunable phosphorescence in KY₃ F₁₀: Tb ³⁺ for x-ray or cathode-ray tubes

We report a persistent phosphor of KY_3(1-x) Tb_3x F₁₀ (KY₃ F₁₀:x Tb³⁺) synthesized by solid-state reaction for x-ray or cathode-ray tubes. The phosphorescence consists of a group of blue and green emission lines originating from ⁵D₃ → ⁷F_J and ⁵D ₄ → ⁷F_J transitions of Tb³⁺, respectively. The phosphorescent emitting color can be tuned from blue to green by gradually increasing Tb³⁺ concentrations, which is attributed to the enhanced ⁵D₃ - ⁵D₄ relaxation through the cross relaxation between two Tb³⁺ ions, as described by of (⁵D₃, ⁷F₆) - (⁵D ₄, ⁷F ₀). The Tb³⁺ concentration dependent phosphorescence spectra are well simulated based on the analysis of luminescence dynamical processes using the Judd-Ofelt theory and rate equations concerning the ⁵ D₃ and ⁵D₄ levels. The energy charge and release pattern of the phosphor are presented and a 10% decay time is 29 s. The measurement of the thermoluminescence glow curve gives convincing evidence for the traps analysis.