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

Ruben Ahumada-Lazo,Samantha J O Hardman,David J Binks,Simon M Fairclough,Sarah J Haigh,Mark Green,Richard J Curry,Rinku Saran,Peter N Taylor

doi:10.1021/acsanm.9b01714

Ruben Ahumada-Lazo, Samantha J O Hardman + Show 7 more

Open Access

https://doi.org/10.1021/acsanm.9b01714

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Abstract

Zinc nitride (Zn3N2) colloidal quantum dots are composed of nontoxic, 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 absorption. The absorption and emission energies are observed to be size-tunable, with the optical band gap increasing from 1.5 to 3.2 eV as the dot diameter decreased from 8.9 to 2.7 nm. Size-dependent absorption cross sections (σ = 1.22 ± 0.02 × 10–15 to 2.04 ± 0.03 × 10–15 cm2), single exciton lifetimes (0.36 ± 0.02 to 0.65 ± 0.03 ns), as well as Auger recombination lifetimes of biexcitons (3.2 ± 0.4 to 5.0 ± 0.1 ps) and trions (20.8 ± 1.8 to 46.3 ± 1.3 ps) are also measured. The degeneracy of the conduction band minimum (g = 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.

Highlights

The size-tunable optical and electronic properties, photostability, and solution-based synthesis and processability of semiconductor nanocrystals, known as colloidal quantum dots (QDs), have motivated research into their suitability for a wide variety of applications, such as photovoltaic cells,[1] photocatalysts,[2] light emitting devices,[3] and biosensors.[4]
The effects of quantum confinement on the optical properties and charge dynamics of a series of Zn3N2 colloidal quantum dots were investigated by optical characterization and ultrafast fluence-dependent transient absorption
The absorption cross section and recombination lifetimes of single excitons, biexcitons, and trions produced at different excitation regimes as well as the degeneracy of the conduction band minimum are all comparable to those of QDs of similar materials

Summary

■ INTRODUCTION

The size-tunable optical and electronic properties, photostability, and solution-based synthesis and processability of semiconductor nanocrystals, known as colloidal quantum dots (QDs), have motivated research into their suitability for a wide variety of applications, such as photovoltaic cells,[1] photocatalysts,[2] light emitting devices,[3] and biosensors.[4]. Perhaps due to difficulties in handling air sensitive materials with high intrinsic surface area, very few studies have reported the synthesis and properties of nanostructured Zn3N2 morphologies,[19,20] with only one work describing the synthesis (see Scheme 1) and optical properties of colloidal Zn3N2 QDs.[21] Importantly, this paper successfully demonstrated the tunability of the optical emission due to quantum confinement effects alongside high photoluminescent quantum yields (35−52%). The optical properties of a series of Zn3N2 quantum dots of different sizes are characterized by transmission electron microscopy and steady-state absorption and photoluminescence (PL) spectroscopies. Article recombination lifetimes are fundamental to the development of Cd- and Pb-free QD-LED displays and other devices such as photovoltaics and biosensors

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES