Size-Dependent Optical Properties of Luminescent Zn3P2 Quantum Dots

Abstract

In the search for more efficient semiconductors with low to nontoxicity, Zn3P2 has gained increasing interest for optoelectronic applications because of its direct band structure, high absorption coefficient, and long carrier diffusion lengths. However, the elucidation of the size-dependent optical properties in the quantum confinement regime has proven a difficult task. This report details a systematic study of the absorption and emission of alkyl-amine-passivated tetragonal Zn3P2 crystallites with varying size (3.2 ± 0.6–8.8 ± 1.3 nm) produced via hot injection of diethyl zinc and tris(trimethylsilyl)phosphine in high boiling alkene/amine medium. The solid-state absorption spectra of nanocrystals (NCs) exhibit substantial blue shifts in the absorption onsets (2.11–2.73 eV) in comparison to the bulk counterpart (1.4–1.5 eV) and a clear red shift with increasing NC size, consistent with the expected quantum confinement effects. The emission properties of NCs were investigated as a function of growth temperature and time and indicate size-tunable maxima in the visible region (469–545 nm) with quantum yields of 0.35–1.6%. Structural and surface analyses of NCs suggest the presence of phase-pure tetragonal Zn3P2 passivated with N–Zn and N–P bonds and the absence of metallic and metal oxide impurities.