In situ analysis of europium calcium oxalate crystallization using luminescence microspectroscopy

Luminescence microspectroscopy (LMS) is described here as an in situ approa ch that combines the spatial resolution and imaging capabilities of optical microscopy with the structural sensitivity of rare earth ion spectroscopy. In this work, LMS, laser-induced luminescence spectroscopy, and convention al Raman spectroscopy were used to analyze the effect of EU3+ admixtures on calcium oxalate crystallization. This new combination of techniques was us ed to establish a link between crystal morphology, phase, and impurity ion bonding environments for single crystals in contact with their aqueous grow th solution. Distinct, spatially resolved EU3+ luminescence spectra were me asured for 1-20 mu m crystals separated by less than 10 mu m. Results show that micromolar quantities of EU3+ significantly inhibit calcium oxalate nu cleation in static, low ionic strength (similar to 2 mM) supersaturated sol utions at room temperature. Eu3+ stabilizes and incorporates into the dihyd rate phase of calcium oxalate and the bipyramidal morphology associated wit h this phase is maintained. EU3+ is believed to occupy Ca2+ lattice sites i n the dihydrate crystals. EU3+ also associates with calcium oxalate monohyd rate during crystallization, yielding several ill-formed crystal morphologi es. Two classes of Eu3+ bonding environments are identified in the monohydr ate, including one with unusual luminescence band energies. The luminescenc e spectra are interpreted in terms of the local structure of the calcium ox alate crystal lattices. These experiments demonstrate LMS to be a useful ap proach for a spatially controlled analysis of inorganic crystal growth at s urfaces in real time. Potential applications include analysis of template-d irected crystallization, biomineralization, phosphors, and ceramic coatings .