Thallium bromide (TlBr) is a dense, high-Z, wide bandgap semiconductor that has potential as an efficient, compact, room temperature nuclear radiation detector. In this paper we report on our recent progress in TlBr nuclear detector development. In particular, improvements in material purification have led to an order of magnitude increase in the mobility-lifetime product of electrons, (mutau)e, to as high as 5 times 10-3 cm2/V. This has enabled much thicker detectors with good charge collection to be fabricated. We fabricated and tested small pixel TlBr arrays up to 10 mm thick. The energy resolution ~2% FWHM at 662 keV was recorded with 5-10 mm thick devices without 3-D spectral correction. We also investigated the long-term detector stability and were able to constantly operate a thin (0.5 mm) detector for five months at -18degC, under an electric field and with irradiation.