Structural evolution study by solid-state NMR of photopolymerizable aluminophosphosilicate hybrid materials

Aluminophosphosilicate materials of composition (mol.%) xSiO ₂[(Al ₂O ₃) ₅₀–(P ₂O ₅) ₅₀] _100-x were prepared through sol-gel method and heat-treated yielding non-crystalline materials. The structural evolution from the hybrid to heat-treated material as a function of the SiO ₂ content was studied by ¹³C, ²⁹Si, ³¹P and ²⁷Al solid-state NMR, infrared spectroscopies, X-ray diffraction and differential scanning calorimetry (DSC). NMR analyses showed the AlPO ₄ formation in the matrix and heterocondensation, forming Al-O-P and P-O-Si linkages. The heat treatment promoted the formation of a more interconnected SiO ₂ tetrahedra network as the SiO ₂ content increased. Similar to the hybrid materials, the increase of SiO ₂ content induces the replacement of P-O-Al(IV) bonds by Si-O-Al(IV) bonds in the heat-treated materials as confirmed by ²⁷Al NMR and ²⁷Al{ ³¹P} REDOR data, which was also supported by Raman analysis. This sol-gel route provides a novel way to fabricate new homogeneous materials, which can be doped with rare earths and applied to new optical devices.