Photoluminescence of Pr³⁺-, Dy³⁺- and Tm ³⁺-doped transparent nanocrystallized KNbGeO₅ glasses

In this paper, we present the photoluminescence properties of Pr ³⁺-, Dy³⁺- and Tm³⁺-doped potassium-niobium- germanate glasses and glass ceramics. From the x-ray diffraction measurement, the glass structure was established. These glasses have shown strong absorption bands in the near-infrared region. Compared with Pr³⁺-, Dy ³⁺- and Tm³⁺-doped glasses, their respective glass ceramics have shown stronger emissions due to the presence of the K _3.8Nb₅Ge₃O_20.4 crystalline phase. For Pr³⁺ -doped glass, two weak emission bands centred at 616 nm(³P₀ → ³H₆) and 648 nm( ³P₀ → ³F₂) and for glass ceramic strong emission bands centred at 533 nm(³P₀ → ³H₅), 616 nm(³P₀ → ³H₆) and 648 nm(³P₀ → ³F₂) along with weak emissions at 688 nm( ³P₁ → ³F₃), 709 nm( ³P₀ → ³F₃) and 732 nm( ³P₀ → ³F₄) have been observed with 450 nm(³H₄ → ³P₂) excitation wavelength. Among them, 648 nm(³P₀ → ³F₂) has shown bright red emission. For the Pr ³⁺ -doped glass and glass ceramic, upconversion emission spectra have also been measured. Bright blue upconversion luminescence was observed under ¹D₂ level excitation. With regard to Dy ³⁺:glass, a weak emission band centred at 576 nm(⁴F _9/2 → ⁶H_13/2) and for glass ceramic a blue emission band centred at 485 nm(⁴F_9/2 → ⁶H_15/2) and a bright fluorescent yellow emission at 576 nm(⁴F_9/2 → ⁶H_13/2) have been observed, apart from ⁴F_9/2 → ⁶H _11/2(664 nm) emission transition with an excitation at 389 nm( ⁶H_15/2 → ⁴I_13/2, ⁴F_7/2) wavelength. Emission bands of ¹G ₄ → ³F₄(650 nm), ³F₃ → ³H₆(707 nm) and ¹G₄ → ³H₅(774 nm) transitions have been observed for the Tm ³⁺:glass and glass ceramic, with an excitation at ³H ₆ → ¹G₄(473 nm). Among them, the ¹G₄ → ³F₄ transition (650 nm) shows bright red emission. The stimulated emission cross-sections of all the emission bands of Pr³⁺, Dy³⁺ and Tm³⁺:glasses and glass ceramics have been computed based on their measured full width at half maximum (Δλ) and lifetimes (τ_m).