Frequency upconversion properties of Yb3+-Er3+co-doped oxyfluoride germanate glass

Abstract

Short wavelength output compact solid state lasers have become one of the most active areas of lasers research and development today [1]. Compared with other techniques, upconversion is of interest because it does not need either stringent constraint of phase matching or of high excitation wavelength stability and the output wavelength is not restricted to a given harmonic. In the past decades, the host materials widely studied for upconversion were fluoride crystals and glasses because fluorides have low nonradiative relaxation rates [2]. However, the mechanical strength, chemical durability and thermal stability of fluoride glasses are generally less than those of oxide glasses. These properties are important for developing rare-earth doped optical fibers. Recently, heavy metal oxide (HMO) glasses, which contain high content of PbO or Bi2O3, have considerable potential as lasing materials such as upconversion and planar optical waveguides [3, 4]. The HMO glasses mainly includes tellurite based glasses, bismuth based materials and germanate based glasses, which are desirable hosts for optically active ions. Of these HMO materials, lead germanate glasses are of growing interest, because they combine higher mechanical strength, chemical durability and better thermal stability even though the maximum phonon energy (810 cm−1) is slightly larger than that of tellurite glasses (750–780 cm−1) [5–8]. In addition, the recent study of glasses containing more than one anion has revealed the possibility of the creation of glasses where the properties are varied by replacing the traditional oxygen by another anion, particularly by halides [9]. The substitution of a fluoride for an oxygen can improve the glass forming behavior of melts and the thermal stability of glasses [10, 11]. However, only a few reports have concentrated on the oxyfluoride germanate glasses and, few investigations have been carried out on the spectroscopic properties of rare-earth doped oxyfluoride germanate glasses. The present paper investigated the upconversion spectroscopic properties of Yb3+Er3+ co-doped 5.5NaF2-8Na2O-11.3PbO-14.5BaF23.6Al2O3-4.1AlF3-51.2GeO2 (mol%; GPAB, hereafter) glass. The doping concentrations of Yb3+ and Er3+ ions were 7.8 × 1020 and 0.78 × 1020 ions/cm3, respectively. The glass sample was synthesized by a conventional melting and quenching method [12]. Reagent grade