Nanocrystalline (Y,Gd)BO3∶Eu with different particle sizes have been prepared by the thermal decomposition of precursors that contain rare earths–EDTA and H3BO3–EDTA complexes (EDTA = ethylenediaminetetraacetic acid). The effects of synthesis temperature, [Y]/[Gd] value, and doping concentration of Eu3+ ions on the crystallization and luminescent characteristics of the (Y,Gd)BO3∶Eu nanocrystals were investigated. The materials began to crystallize at 700 °C in air or 650 °C in oxygen with a hexagonal vaterite-type structure, except that a small amount of triclinic phase was seen at a low [Y]/[Gd] value. By increasing the [Y]/[Gd] value and the calcination temperature, the triclinic phase could be eliminated. XRD patterns indicated that (Y,Gd)BO3∶Eu nanocrystals with smaller particle size possessed a more distorted lattice, which could be responsible for the size-dependent color purity evidently showed in their photoluminescence spectra, as the ratio of the red emission (5D0
→
7F2) to the orange emission (5D0
→
7F1)
(R/O) was much higher in the smaller particles. The Eu3+ quenching concentration and the optimum Gd3+ substitution also exhibited the size-dependent characteristics. Their possible mechanisms were proposed.
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