The design of a process to create yttrium aluminosilicate microspheres with a core-shell structure is of interest in the field of cancer brachytherapy. Glass microspheres with yttrium-depleted shell may indeed reduce the risk of Y-90 release into the organism. Here we show - by means of confocal micro-Raman scattering, microfluorescence, X-ray-fluorescence analysis, and IR spectroscopy - that yttrium depletion may be achieved by etching in HCl solution (pH 2) at a rate of 1 mu m day(-1) in bulk glass and 3 mu m day(-1) in glass microsphere (35 mu m of diameter). Importantly, the spectroscopic results - collected in confocal configuration along the processed layer - indicate a high degree of structural reconstruction of the glass network, with the formation of an interconnected silicate-rich glass that surrounds a core of unmodified yttrium aluminosilicate. We also demonstrate that the process is driven by non-bridging oxygen sites, which regulate the hydroxylation and structural reconstruction of the glass within the Y-depleted layer. The analysis gives also some insight into open fundamental questions about the short-range structure and the chemical stability of this kind of glass, which is also important in photonics and nuclear waste disposal. (C) 2012 Elsevier B.V. All rights reserved.