Whitish fluorescence of partially Ag-exchanged zeolite Y affected by coexisting cations

A single material with a whitish fluorescence was found from silver exchanged zeolite Y. We obtained that material by washing zeolite Y (cation exchange capacity: 3.34 mmol/kg) with AgNO₃ solutions followed by heat treatments. Their fluorescence spectra were composed of two peaks (peak-1: 448 nm; peak-2: 503 nm) with excitation at 230–320 nm. The fluorescence intensity of the two peaks increased up to an Ag-exchange amount of 0.5 mmol/g, but a further increase in the amount decreased the intensity of the two peaks. Heating treatments up to 500 °C increased the fluorescence intensity, especially of peak-1. Alkali metal cations coexisting with Ag in the partially Ag-exchanged zeolite Y also affected the fluorescence intensity, and the co-existence of Li⁺ significantly increased the intensity of a peak-1. The maximum fluorescence intensity (internal quantum yield: 41%) was observed at a 0.5 mmol/g Ag-exchange with the coexistence of 1.30 mmol/g of Li⁺ and 1.54 mmol/g of Na⁺ after heating at 500 °C.