| Abstrakt: |
Luminescence microspectroscopy (LMS) is described here as an in situ approach 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 conventional Raman spectroscopy were used to analyze the effect of Eu3+ admixtures on calcium oxalate crystallization. This new combination of techniques was used to establish a link between crystal morphology, phase, and impurity ion bonding environments for single crystals in contact with their aqueous growth solution. Distinct, spatially resolved Eu3+ luminescence spectra were measured for 1−20 μm crystals separated by less than 10 μm. Results show that micromolar quantities of Eu3+ significantly inhibit calcium oxalate nucleation in static, low ionic strength (~2 mM) supersaturated solutions at room temperature. Eu3+ stabilizes and incorporates into the dihydrate phase of calcium oxalate and the bipyramidal morphology associated with this phase is maintained. Eu3+ is believed to occupy Ca2+ lattice sites in the dihydrate crystals. Eu3+ also associates with calcium oxalate monohydrate during crystallization, yielding several ill-formed crystal morphologies. Two classes of Eu3+ bonding environments are identified in the monohydrate, including one with unusual luminescence band energies. The luminescence spectra are interpreted in terms of the local structure of the calcium oxalate crystal lattices. These experiments demonstrate LMS to be a useful approach for a spatially controlled analysis of inorganic crystal growth at surfaces in real time. Potential applications include analysis of template-directed crystallization, biomineralization, phosphors, and ceramic coatings. |
