Concentration dependence of visible luminescence from Pr³⁺-doped phosphate glasses

To clarify the concentration dependence of visible fluorescence of Pr³⁺, a series of phosphate glass samples with Pr³⁺ concentration from 0.05 to 3.0 mol% were fabricated. Steady and dynamic spectroscopic characteristics of Pr³⁺-doped phosphate glasses were systematically investigated. When the Pr³⁺ concentration was small, only one visible fluorescence band can be observed at 596 nm, which was ascribed to the transition of ¹D₂ → ³H₄. With increasing Pr³⁺ concentration from 0.05 to 0.5 mol%, since the multi-phonon relaxation rate of ³P₀ was largely quicker than that of ¹D₂. Increasing Pr³⁺ concentration from 0.5 to 3 mol%, increasing two other fluorescence bands at 612 nm and 640 nm, which were assigned to the transitions of ³P₀ → ³H₆ and ³P₀ → ³F₂, respectively. It was due to the cross relaxation probability between [¹D₂: ¹G₄] and [³H₄: ³F₄] increased, which results in quicker decay rate of ¹D₂. The fluorescence lifetime of ¹D₂ decreased from 173 to 6 μs with increasing Pr³⁺ concentration from 0.1 to 3 mol%, which due to the cross relaxation probability between [¹D₂: ¹G₄] and [³H₄: ³F₄] increased, resulting in quicker decay rate of ¹D₂. Fitting the concentration dependence of fluorescence lifetime demonstrated that the cross relaxation arising from dipole-dipole interactions between Pr³⁺ ions.