We have recently demonstrated efficient high power CW laser operation in Er doped Y2O3 at cryogenic temperature. The selection of laser host was based on the low-phonon nature of Y2O3, where the 4I11/2 →4I13/2 transition is highly radiative. Further increases in mid-IR power scaling and efficiency require in-depth study and analysis of basic spectroscopic properties of the 4I11/2 → 4I13/2 laser transition, such as laser emission cross- sections, fluorescence quantum efficiency, fluorescence branching ratios and inter-ionic interactions in a wide dopant-concentration and temperature range. In this work, we report the results of experimental measurements of quantum efficiency and branching ratio of the erbium initial laser state of 4I11/2 in Y2O3 ceramic at the temperature range of 10 - 300 K. A series of Er:Y2O3 samples with dopant concentration between 0.2-10 at.% were used for fluorescence and absorption measurements. The fluorescence from the energy states corresponding to the visible, IR, and mid-IR transitions were studied under shortpulsed diode laser excitation. Spectrally-narrowed fiber-coupled semiconductor laser modules emitting at ~ 808, 980, and 1530 nm with variable power density were used for fluorescence excitation of three different Er states. The energy transfer processes for both down- and up-conversion, affecting the Er:Y2O3 mid-IR laser operation, were analyzed. A comparison between the experimental and simulation results are presented as well.