Energy level decay and excited state absorption processes in dysprosium-doped fluoride glass

The primary excited state decay processes relating to the $H613/2→H615/2∼3μm$ laser transition in singly $Dy3+$-doped fluoride (ZBLAN) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the $F69/2$⁠, $H67/2$ energy levels at 1125 nm and $F611/2$⁠, $H69/2$ energy levels at 1358 nm established that the energy levels above the $H611/2$ level, excluding the $F49/2$ level, are entirely quenched by multiphonon emission in ZBLAN glass. The $H611/2$ and $H613/2$ energy levels emit luminescence with peaks at $∼1700$ and $∼2880nm$⁠, respectively, but at low quantum (luminescence) efficiencies. The quantum efficiency of the $H611/2$ level and $H613/2$ level is $∼9×10−5$ and $∼1.3×10−2$⁠, respectively, for $[Dy3+]=0.5mol%$ based on calculations of the radiative lifetimes using the Judd–Ofelt theory. Excited state absorption (ESA) was detected by monitoring the rise time of the 1700 nm luminescence after tuning the probe wavelength across the spectral range from 1100 to 1400 nm. As a result of nonradiative decay of the higher excited states, ESA contributes to the heating of $∼3μm$ fiber lasers based on $Dy3+$-doped fluoride glass. For $[Dy3+]$ up to 4 mol %, we found no evidence of energy transfer processes between $Dy3+$ ions that influence the decay characteristics of the $H611/2$ and $H613/2$ energy levels.