Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors

Europium ion-activated calcium silicate phosphors (Ca₂SiO₄:Eu³⁺) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca₂SiO₄:Eu³⁺ 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 Ca₂SiO₄:Eu³⁺ phosphors depend on their particle sizes. Particularly, the Ca₂SiO₄:Eu³⁺ 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 Ca₂SiO₄:Eu³⁺ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of ⁵D₀ → ⁷F₄ 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 Ca₂SiO₄:Eu³⁺ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.