Mechanism Responsible for Changes in the Luminescence Properties of Terbium (III)–Doped Layered Double Hydroxides During Carbonate/Chloride Exchange

Layered double hydroxides (LDHs) have been actively studied as water purification, battery, capacitor, and catalytic materials because they exhibit anion-exchange capabilities. Furthermore, photoluminescent LDHs are potentially useful as materials capable of detecting toxic anions. These materials can be synthesized using various combinations of divalent and trivalent metal cations. Herein, we investigate the synthesis and photoluminescence (PL) properties of Mg (Al, Tb)-LDHs with different incorporated interlayer anions, specifically carbonate (CO₃²⁻) and chloride (Cl⁻). The CO₃²⁻-incorporated Mg (Al, Tb)-LDH was synthesized using a hydrothermal method, whereas Cl⁻ was introduced through anion exchange. Characterization techniques confirmed that Tb³⁺ has been successfully doped into the LDH structure without impurities. The CO₃²⁻-incorporated Mg (Al, Tb)-LDH was significantly more photoluminescent than its Cl⁻ counterpart. However, further analysis using electron spin resonance and X-ray absorption fine structure techniques revealed that the Tb³⁺ electronic state is unaffected by the anionic species. Synchrotron radiation X-ray diffractometry and subsequent Rietveld analysis revealed that thermal fluctuations of the anionic species and hydrated water in the interlayer space are the primary factors that influence PL intensity. These findings highlight the crucial role played by the thermal stabilities of the interlayer components in determining the PL properties of Mg (Al, Tb)-LDH.