Photoluminescence of Pr3+-, Dy3+- and Tm3+-doped transparent nanocrystallized KNbGeO5 glasses

In this paper, we present the photoluminescence properties of Pr3+-, 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+-, Dy3+- and Tm3+-doped glasses, their respective glass ceramics have shown stronger emissions due to the presence of the K3.8Nb5Ge3O20.4 crystalline phase. For Pr3+-doped glass, two weak emission bands centred at 616 nm(P-3(0) -> H-3(6)) and 648 nm(P-3(0) -> F-3(2)) and for glass ceramic strong emission bands centred at 533 nm(P-3(0) -> H-3(5)), 616 nm(P-3(0) -> H-3(6)) and 648 nm(P-3(0) -> F-3(2)) along with weak emissions at 688 nm(P-3(1) -> F-3(3)), 709 nm(P-3(0) -> F-3(3)) and 732 nm(P-3(0) -> F-3(4)) have been observed with 450 nm(H-3(4) -> P-3(2)) excitation wavelength. Among them, 648 nm(P-3(0) -> F-3(2)) has shown bright red emission. For the Pr3+-doped glass and glass ceramic, upconversion emission spectra have also been measured. Bright blue upconversion luminescence was observed under D-1(2) level excitation. With regard to Dy3+ : glass, a weak emission band centred at 576 nm(F-4(9/2) -> H-6(13/2)) and for glass ceramic a blue emission band centred at 485 nm(F-4(9/2) -> H-6(15/2)) and a bright fluorescent yellow emission at 576 nm(F-4(9/2) -> H-6(13/2)) have been observed, apart from F-4(9/2) -> H-6(11/2) (664 nm) emission transition with an excitation at 389 nm(H-6(15/2) -> I-4(13/2), F-4(7/2)) wavelength. Emission bands of (1)G(4) -> F-3(4)(650 nm), F-3(3) -> H-3(6)(707 nm) and (1)G(4) -> H-3(5)(774 nm) transitions have been observed for the Tm3+ : glass and glass ceramic, with an excitation at H-3(6) -> (1)G(4)(473 nm). Among them, the (1)G(4) -> F-3(4) 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 (Delta lambda) and lifetimes (tau(m)).