Structural Order–Disorder Effects and Photoluminescence Behavior in Aluminum-Doped CaCu₃Ti₄O₁₂: A Comprehensive Review

Calcium copper titanate (CaCu₃Ti₄O₁₂ – CCTO) has attracted significant attention due to its remarkable dielectric, optical, and photoluminescent properties. In particular, structural disorder at short and medium range has been strongly correlated with visible photoluminescence (PL) emission at room temperature. This review discusses the structural, vibrational, optical, and electronic modifications induced by aluminum doping in CCTO, emphasizing the role of order–disorder transitions, cluster formation ([TiO₆], [TiO₅], and [AlO₆]), oxygen vacancies, and band gap modulation. Special attention is given to thermal evolution between 300 °C and 800 °C, where coexistence between amorphous and crystalline domains leads to maximum PL intensity. Spectroscopic evidence from XRD, FT-IR, Raman, UV–Vis, and photoluminescence analyses is critically interpreted to establish correlations between local structural rearrangements and electronic transitions. The review consolidates experimental findings and theoretical interpretations, highlighting aluminum as an electron acceptor dopant capable of modifying defect density and tuning optical gap energies.