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 K₄-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.