Unravelling the role of volatile hydrogenous species in the defect dynamics of CBD-grown ZnO submicron crystals via temperature-dependent luminescence

Hexagonal wurtzite ZnO submicron crystals were synthesized via low-temperature chemical bath deposition. In-situ temperature-dependent photoluminescence spectroscopy revealed an anomalous thermal evolution of point defects. In the as-grown crystals, a sudden appearance of green emission (2.45 eV) at 350 K and a negative thermal quenching of the free exciton line up to 475 K were observed. This non-monotonic behavior is attributed to the thermal desorption of volatile hydrogen/hydroxyl species ( 𝐻 𝑖 , 𝑂 ⁢ 𝐻 , 𝐻 2 ⁡ 𝑂 ) and subsequent structural relaxation. Following annealing at 675 K, the crystals exhibited stabilized thermal quenching. Arrhenius and Varshni approximations yielded defect activation energies and quantified a significant increase in the Debye temperature ( 𝛽 ) from 388 to 465 K for the free exciton line. This quantitative shift provides direct evidence of a “local lattice hardening” effect resulting from the minimization of metastable defects and internal strain relaxation.

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