Thermal Oxidation-Driven Phase Control of CuO-Cu2O Hybrids on Copper Substrates for Tunable Optical Functionalities

CuO-Cu2O hybrid materials were developed through a simple single-step thermal oxidation process of copper plates. Copper substrates were annealed at a temperature range of 300 to 700 °C. To investigate the temperature-driven transitions in oxide composition, crystallography, and photonic response, various analytical techniques were employed. X-ray diffraction (XRD) confirmed the progressive transformation, accompanied by changes in phase fraction and structural modification. Fourier-transform infrared spectroscopy (FT-IR) and photoluminescence (PL) identified vibrational and emission features associated with bonding and oxide defect states, respectively. UV-Vis spectroscopy revealed a tunable bandgap between 2.60 and 2.55 eV, influenced by phase composition. Improved optical functions were observed at different heating temperatures. In this study, the thermal oxidation of a copper plate is proposed as a scalable strategy for phase-controlled oxide synthesis, suggesting that the synthesized CuO-Cu2O hybrids are considered for application in opto-related technology. HIGHLIGHTS Oxidation driven by temperature showed the formation of CuO and Cu2O at 500 °C. At 700 °C, Cu2O remains the main phase because gas exchange is limited by phase equilibrium. Oxide phases reveal at 700 °C heating present the most significant lattice improvement. SEM analysis showed dense, fine grains at 300 °C transforming into larger, porous crystallites (400 nm) at 700 °C, indicating lattice strain relaxation and recrystallization. Tailored optical behavior with bandgap modulation from 2.69 to 2.55 eV with increasing heating temperature. At 700 °C heating, skin depth increased and optical density reduced, reflecting superior light penetration and low photon scattering. GRAPHICAL ABSTRACT