Effect of temperature on the morphology of rare earth-doped microcapsules

Fluorescent microcapsules doped with europium β-diketone complex were previously fabricated by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer (LbL) technique [Chem. Commun. (2007) 1547-1549]. In this work, the influence of thermal treatment on the morphology of rare earth-doped microcapsules was studied by atomic force microscopy (AFM). Remarkable shrinking, increase of wall thickness and decrease of surface roughness were observed after heating the rare earth-doped microcapsules until 70 °C for 30 min. Intense red light emission at 612.0 nm of the microcapsules could be clearly observed by bare eyes after thermal treatment. Diameter variation of the luminescent microcapsules induced by annealing is attributed to the molecular rearrangement of polyelectrolytes. Study on the fluorescent microcapsules with various sizes provides guidance in potential application as biological assay reagents or display elements.