Effect of coexisting lithium content on fluorescent properties of silver ion-exchanged LTA zeolite

Abstract

The effect of the lithium ion coexistence on the fluorescent properties was studied for a partially Ag-exchanged LTA (A-type) zeolite. A series of Ag–Li-LTA zeolite samples was prepared by mixing the LTA zeolite powder (1.0 g) with aqueous solutions (100 mL) containing AgNO₃ (0.5 mmol) and various amounts of LiNO₃ (0–100 mmol). Although the fluorescence intensity was hardly observed in the unheated state for the Ag-LTA and the Ag–Li-LTA zeolites, the intensity was enhanced by the heat-treatment and showed the maximum value for the samples heated at 600 °C. A dramatic enhancement in the fluorescence intensity was observed by increasing the amount of the Li addition with a heat treatment at 600 °C. The highest fluorescent intensity was reached for the Ag(2.8%)–Li(72.6%)-LTA zeolite doped using the solution containing 0.5 mmol/g AgNO₃ and 100 mmol/g LiNO₃. Furthermore, the fluorescence shifted from a 605 nm (yellow) to the shorter wavelength of 505 nm (green) with the increasing Li amount. The fluorescent intensity due to the coexisting lithium ion for the Ag-exchanged LTA zeolite was significantly superior to those of the Ag–Li-FAU(X- and Y-types) zeolites.