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Europium ion-activated calcium silicate phosphors (Ca 2 SiO 4 :Eu 3+ ) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca 2 SiO 4 :Eu 3+ phosphors was controlled between 20 and 200 nm by precursor silicate particle sizes. Systematic studies to determine morphology, crystal phase, and photoluminescence (PL) were carried out for all the phosphors, and their optical efficiencies were compared. We found that the luminescence intensity and emission wavelength of Ca 2 SiO 4 :Eu 3+ phosphors depend on their particle sizes. Particularly, the Ca 2 SiO 4 :Eu 3+ synthesized with 20 nm silica seed contains the most intense red emission, high color purity, and high PL quantum yield. For the 20 nm-sized Ca 2 SiO 4 :Eu 3+ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of 5 D 0 → 7 F 4 emission (712 nm) is explained by structural distortion arising from silicate particle size reductions. We show that the obtained phosphor is a suitable candidate for solid-state lighting as a red component through CIE chromaticity coordinate and color purity measurements. Furthermore, the Ca 2 SiO 4 :Eu 3+ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.

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