Fine yttrium oxide powders doped with Yb 3+ and co-doped either with Tm 3+ or Ho 3+ were synthesized via spray pyrolysis at 900 °C using 0.1 M nitrate precursor. Synthesized powders were additionally thermally treated at 1100 °C for 24 h. The characterization was done through X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescent measurements (PL). Generation of cubic bixbyte-structure with space group Ia-3 is confirmed in all samples. Spherical particles with the mean size of ∼400 nm, generated through volume precipitation of much smaller nanograins, expose certain degree of porosity which alters particle morphology during additional thermal treatment. Powders optical characterizations include measurement of up-conversion emission spectra after excitation at 978 nm, as well as determination of emission lifetimes and up-converted emission intensity dependence on excitation power. Dominant green ( 5F 4, 5S 2 → 5I 8) and blue ( 1G 4 → 3H 6) emission is found for Ho 3+ and Tm 3+ samples, respectively. The amplified emission intensities and enhanced lifetime in thermally treated samples are correlated with the powders morphological and structural changes.