© 2017 IOP Publishing Ltd and Sissa Medialab. We calibrate a two-phase xenon detector at 0.27 keV in the charge channel and at 2.8 keV in both the light and charge channels using a37Ar source that is directly released into the detector. We map the light and charge yields as a function of electric drift field. For the 2.8 keV peak, we calculate the Thomas-Imel box parameter for recombination and determine its dependence on drift field. For the same peak, we achieve an energy resolution, Eσ/Emean, between 9.8% and 10.8% for 0.1 kV/cm to 2 kV/cm electric drift fields.