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In this paper, an oxide upconversion nanomaterial, Gd2O3:Ln3+, as an alternative counterpart of NaGdF4:Ln3+ was developed via controlled surfactant-free synthesis, flexible lanthanide loading, compositional/size tuning, hexagonal-to-cubic lattice refinement, and positive surface charging to achieve a substantial enhancement of upconversion luminescence (∼30 times upon calcination at 1000 vs 600 °C; ∼4000 times versus its hydroxide form) due to high crystallinity and extremely low residual impurities for white emission and cellular imaging.