Confinement Effects and Charge Dynamics in Zn3N2 Colloidal Quantum Dots: Implications for QD-LED displays

Zinc nitride (Zn3N2) colloidal quantum dots are composed of non-toxic, low-cost and earth-abundant elements. The effects of quantum confinement on the optical properties and charge dynamics of these dots are studied using steady state optical characterization and ultrafast fluence-dependent transient ab-sorption. The absorption and emission energies are observed to be size tunable, with the optical band gap increasing from 1.5 eV to 3.2 eV as the dot diameter decreased from 8.9 nm to 2.7 nm. Size dependent absorption cross sections (σ = 1.22 ± 0.02 × 10-15 cm2 to 2.04 ± 0.03 × 10-15 cm2), single exciton lifetimes (0.36 ± 0.02 ns to 0.65 ± 0.03 ns), as well as Auger recombination lifetimes of biexcitons (3.2 ± 0.4 ps to 5.0 ± 0.1 ps) and trions (20.8 ± 1.8 ps to 46.3 ± 1.3 ps) are also measured. The degeneracy of the con-duction band minimum (푔 = 2) is determined from the analysis of the transient absorption spectra at different excitation fluences. The performance of Zn3N2 colloidal quantum dots thus broadly matches that of established visible light emitting quantum dots based on toxic or rare elements, making them a viable alternative for QD-LED displays.