High-purity (99.999%) Y2O3 powder is used as a starting material for fabricating high-temperature superconductors (HTS), and is frequently found as an unreacted second phase in the final product. We have found that as-received Y2O3 contains Tb3+ paramagnetic impurity ions as determined by TSL and emission-spectra measurements. Deep luminescence traps (presumably Tb4+ ions) are formed in Y2O3 when it is exposed to frays, x rays, or fluorescent lights. These deep traps can only be removed by annealing the material to near 1600°C. Given the short coherence length of HTS it is possible that order-of-magnitude variations in the Tb impurity concentration of starting materials may affect the ultimate value of surface resistance (Rs).