The thermal transformation of Eu3+-doped and undoped microporous titanosilicate AM-3 has been reported. AM-3 is stable up to 600 degrees C and transforms into the analogue of the mineral narsarsukite at 800 degrees C. The narsarsukite obtained from AM-3 is purer than that prepared from the titanosilicates ETS-10, ETS-4 and AM-1, and is suitable for hosting optically-active Ln(3+) ions. The materials have been studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), Raman and photoluminescence spectroscopies.