Blue Luminescence of ZnO Nanoparticles Based on Non‐Equilibrium Processes: Defect Origins and Emission Controls

TLDR

The study investigates blue luminescence in ZnO nanoparticles produced by non‑equilibrium processes, aiming to analyze defect origins and control emission characteristics. The authors attribute blue emission to interstitial‑zinc defect levels, supported by EPR evidence of interstitial zinc and its evolution with annealing. ZnO nanoparticles exhibit strong blue emission whose intensity rises then falls with annealing, shows excitation dependence with optimal energy near the bandgap, fixed wavelengths at 415–488 nm, and allows controllable co‑emission of blue and green shifting peaks from blue to yellow.

Abstract

Abstract High concentrations of defects are introduced into nanoscale ZnO through non‐equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420 nm (2.95 eV < E g = 3.26 eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488 nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial‐zinc‐related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as‐prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co‐emission of blue and green emissions and peak adjustment from blue to yellow.