a Weight change and heat flow recorded for Na
O nanobelts. b XRD pattern of NaNbO3 nanobelts (a) and the standard pattern of bulk NaNbO3 (b). c UV–Vis spectra of (a) Na7(H3O)Nb6O19·14H2O nanobelts, (b) NaNbO3 nanobelts, and (c) bulk NaNbO3. d Room temperature PL spectra of NaNbO3 nanobelts, the inset shows an enlarged spectrum.