A series of nanocrystals Y_1-xEu_xVO₄ (x = 0–0.1) were prepared by isothermal and isochronal hydrothermal reactions using citric acid as the capping agent. All nanocrystals were controlled to show particle sizes ranging from 7 to 36 nm, which gives rise to the grain growth kinetics in terms of an equation, D⁵ = 6.71⁵ + 2.82 × 10¹⁰t exp(−51.50/RT) for x = 0.05. Structural refinements of these nanocrystals demonstrate that as particle size reduces, there appeared an abnormal lattice expansion. The expansion rate is strikingly dependent on the substitution content of Eu³⁺ in Y_1-xEu_xVO₄. Namely, higher Eu³⁺ content led to a larger lattice expansion. With these structural changes, nanocrystals of Y_0.90Eu_0.10VO₄ were found to show the maximum luminescence performance as represented by a long lifetime of 1.33 ms. The findings reported in this work are fundamentally important, which might be extended to other doped phosphors with controlled grain growth kinetics for advanced properties.