Ligand Induced Morphology Change and Enhancement of Luminescence Emission in CaF2:Eu(III) Nanoparticles: The Role of Ethylene Glycol, Trisodium Citrate and EDTA in Tuning the Particle Size in Seeded-Growth Approach

Ethylene glycol (EG), citrate and EDTA stabilized Eu(III) doped CaF2 nanoparticles were synthesized following colloidal precipitation method. With EDTA, highly monodisperse cubic nanoparticles (NPs) were formed which changes to quasi-spherical morphology when the capping ligand changes to TSC and EG associated with a broader size distribution. Generations of larger NPs were produced through kinetically controlled seeded-growth method where the ligands directly affect the size tunability. The homogeneity of the growth process was maximized by the adjustment of reaction parameters like temperature and concentration of precursor. Under the same reaction conditions, better kinetic control of the growth process and the ease of tuning the size by the ligands follow the order: EDTA > citrate > EG. The Eu3+ emission intensities characteristic of 5D0 → 7Fn for the NPs increases when the ligand changes from EG to EDTA through citrate. Among the generations of NPs capped by a particular ligand, the dependence of luminescence intensity on size is observed. With decreasing size, there is luminescence enhancement for NPs stabilized by citrate and EDTA while the trend is opposite for EG stabilized particles.