Abstract
Enhanced 1.8μm emission from Tm3+ by Yb3+ sensitization and bubbling in tungsten tellurite glasses has been demonstrated under the excitation of a 976nm laser diode. Radiative properties such as spontaneous emission probabilities, radiative lifetimes and fluorescence branching ratios along with absorption and emission cross sections have been calculated from the absorption spectra. The influences of Yb3+ concentration, Tm3+ concentration, and bubbling time on spectroscopic properties have been thoroughly investigated. It is found that with increasing the bubbling time to 35min, OH− content deceases sharply while 1.8μm emission intensity improves greatly and 3F4 level lifetime prolongs to 1.57ms close to radiative time. After 35min, they change very little due to almost reaching the dynamic balance. The strength of interaction between Tm3+ and OH− is determined. The energy transfer mechanism between Yb3+ and Tm3+ is proposed by photoemission spectroscopy and lifetime measurement. The energy transfer coefficients have been analyzed by the extended spectral overlap method and hopping model. Large ratio of the forward energy transfer from Yb3+ to Tm3+ to the backward one (223) and high energy transfer efficiency (97%) from Yb3+ to Tm3+ ensure efficient 1.8μm emission. Hence, Yb3+ sensitization and the reduction of OH− content could be expected to open up a possibility to achieve high efficient 2.0μm lasing from Tm3+ under a 976nm LD pump.
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