Phosphate glasses activated with Yb3+ ions.
The advantages of Yb-activated laser materials have been recognized for generation of ultra-short pulses and high peak powers . In comparison to neodymium phosphate laser glasses, the use of Yb as activator has some advantages: a simple electronic structure of Yb ions avoids concentration quenching of luminescence and excited-state absorption. The relatively long fluorescence lifetime and the broad absorption and emission bands allows to consider Yb-doped glasses as attractive material for generation of ultra short pulses and high-power pulse amplification. Phosphate glasses exhibit a wide transmission range, high solubility for rare earth ions, long fluorescence lifetime and tailorable properties by changes of the glass composition [2,3]. The aim of this paper is to clarify the conditions of preparation of Yb-containing phosphate glass samples with high optical quality and low concentration OH- ions and to study their optical and luminescent properties depending on both Yb2O3 content in the range of 1 - 5 mol.% and time of dry oxygen bubbling.
Phosphate glasses with nominal compositions (100 – X) (52,2 P2O5, 8,4 BaO, 17,0 K2O, 5,35 SiO2, 9,6 Al2O3, 7,4 B2O3) + XYb2O3(Х= 1÷ 5) were prepared using phosphoric acid, boric acid, aluminum hydroxide, carbonates of barium and potassium, silicon and ytterbium oxides as raw materials. All chemicals used in the synthesis were of “high pure” and “chemically pure” grade. Batches were calculated to yield 200 g of glass and were mixed homogeneously in silica glass crucible and subsequently melted in a platinum crucible at 1400 °C for about 1 h in air and up 1 to 6 hours with dry oxygen bobbling with pouring out of melt in a steel mold and finally annealing at 450÷ 550°C for 4 h. Absorption spectra, excitation and emission spectra and luminescence decay curves were recorded with the use of conventional techniques. All measurements were carried out at room temperature.
Luminescence quenching is established to absent for Yb3+ content up to 8∙1020 ions/cm3 (i.e. ~3,5 mol.% Yb2O3) that may be connected with relatively small efficiency of donor-donor energy migration in these glasses. As a result the Yb3+-activated glasses show luminescence quantum yield 93% for glasses with 1 mol% Yb2O3 and even for heavily activated glasses with 5 mol.% Yb2O3 luminescence quantum yield is higher 45%. The influence of pumping wavelengths on the lifetime of Yb3+ was also investigated and the optimal excitation wavelength for studying the kinetics of luminescence quenching was determined. The luminescence efficiency of glasses was found to be the function of not only Yb2O3 content but also glass drying time. It was shown that the glass dehumidification procedure should be continued at least 3 hours. The optimal duration of glass melt drying was determined taking into account both the absorption coefficient value at 3100 nm (absorption band of OH ions) and a change in the luminescence decay time for each Yb3+ concentration.
Achieved properties of synthesized phosphate glasses in combination with their manufacturability refer them to promising heavily doped laser materials.
This work is financially supported by the Ministry of Education and Science of the Russian Federation (grant 14.Z50.31.0009).
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