Laser-driven phase transformations and surface phonon dynamics in ZnO/MnO nanocomposites

Abstract Raman spectroscopy, widely applied to probe phonon dynamics in nanomaterials, is often considered non-destructive; however, localized laser-driven heating may significantly affect vibrational and structural responses in thermally sensitive systems. We present a systematic Raman spectroscopic study of laser-driven nanostructuring, phase evolution, and surface optical-phonon behavior in ZnO/MnO nanocomposites over a broad range of MnO concentrations (5–95%). Laser power density was varied, from 159 to 955 kW/cm 2 , during Raman measurements to evaluate its influence on phonon behavior and phase stability. A critical laser power threshold of 40 mW (637 kW/cm 2 ) was identified at 30% MnO concentration, where a Raman mode near 258 cm −1 splits into two components, providing direct spectroscopic evidence of this phase transition involving MnO-related intermediate phases. At higher manganese concentrations, the Raman response reveals a complex coexistence and evolution of manganese-related phases, including MnO, Mn 2 O 3 , MnO 2 , MnOOH, Mn 3 O 4 , ZnMn 2 O 4 , and ZnMnO 3 . Surface-related vibrational modes progressively weaken and disappear with increasing manganese content and laser power, indicating a transition from zinc oxide to manganese oxide-dominated structures. These findings highlight the decisive role of laser excitation conditions in Raman spectroscopy and provide practical guidance for interpreting measurements of thermally sensitive mixed-oxide nanomaterials.