Effect of ion exchange on photoluminescence of layered niobates K4Nb6O17 and KNb3O8

Layered niobates K4Nb6O17 and KNb3O8 showed bright blue emission at 77 K. The luminescent properties were changed by exchanging potassium ions at interlayers with other cations. The luminescent intensity of NH4+-exchanged K4Nb6O17 was higher than that of native K4Nb6O17 In contrast, for H+-exchanged K-4-Nb6O17 and KNb3O8, the luminescent intensities decreased and the emission spectra red-shifted compared with their native layered niobates. The sharp and strong Raman bands (880 cm(-1) for K4Nb6O17 and 955 cm(-1) for KNb3O8) assigned to short Nb-O bonds which stuck out into interlayers were observed for the native layered niobates. The Raman bands were decreased by H+ exchange corresponding to the luminescent intensity. These results indicated that characteristics of the short Nb-O bonds were changed by cation exchange at interlayers, resulting in the change in the energy state of niobate layers. Thus, it was demonstrated that photophysical properties of niobate layers could be controlled by substances at interlayers.