Improved ultrafast free-excitonic luminescence of ZnO microcrystals grown by carbothermal reduction method

Abstract

High quality ZnO microcrystals were successfully grown by carbothermal reduction method. SEM images revealed that the grown crystals are tetrapod like structures which could be classified into different types depending on the number of legs and junctions. The grown ZnO microstructures exhibit ultrafast excitonic luminescence at ~380 nm with slow component (33 ps - 250 ps) and fast component (<5 ps - 52 ps). The increasing decay time is due to decreasing coherence volume of the exciton in the crystal. Coherence volume decreases in the presence of crystal defects such as dislocation and lattice mismatch on the junction of the tetrapod. Thus, the decay of free-excitonic luminescence of ZnO crystals could be improved into few picoseconds by synthesizing ZnO crystals with high quality. Suppresion of 437 cm^-1 E2 mode peak of Raman spectra at the junction compared to the leg suggest that the leg has more crystal uniformity than at the junction.