Quantifying and Understanding Stimulated Emission from Bulk PbS Nanocrystals with Vanishing Confinement

Jan Matthys^a^,^b, Alexander Arutunyan^a^,^b, Nastaran Kazemi Tofighi^a^,^b, Shuaijun Liu^c, Ranjana Yadav^a, Pieter Geiregat^a^,^b

^aDepartment of Chemistry, Physics and Chemistry of Nanostructures Group, Ghent University, Belgium

^bNOLIMITS Center for Non-Linear Microscopy and Spectroscopy, Ghent University, Belgium

^cSchool of Chemistry and Molecular Engineering, East China University of Science and Technology, China

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)

Advances in Nanocrystals: Fundamental approaches and technological perspectives - #NCAdv

Sevilla, Spain, 2025 March 3rd - 7th

Organizers: Carmelita Rodà and Matteo Zaffalon

Poster, Jan Matthys, 655
Publication date: 16th December 2024

Colloidal nanocrystals (NCs) are prized for their solution processability and tunable optical properties, enabling applications like photodetectors and light-emitting diodes. In addition to these, NCs have also been shown to provide net stimulated emission1, and quasi-CW lasing has been demonstrated in the visible region2. For the infrared spectrum, due to the absence of organic molecules or perovskites with an IR bandgap, semiconductor nanocrystals remain the only option for solution processable materials. In this category, lead salts are an attractive candidate. Indeed, PbS quantum dots have been used as the gain material to enable optically pumped lasers and more recently, lasing far in to the short-wave IR region past 2400 nm3,4. Despite these pioneering results, it remains unclear what drives their performance and whether a further push to larger sizes would be as beneficial as was shown recently for CdS and CdSe “bulk” nanocrystals in the visible range2. The promise of reduced Auger recombination and lower gain thresholds when approaching the bulk limit remains unvalidated for lead-chalcogenides.
In this poster, I will discuss the evolution of the properties of a set of PbS nanocrystals with a diameter ranging from 5 to 20 nm. In particular, I will discuss the optical gain properties derived from extensive size-dependent IR transient absorption measurements. Our results indicate that a transition to larger sizes leads to a consequent increase in gain lifetime, reduced carrier density for transparency and a rather size-independent gain coefficient.
Further on, I will give an explain for the unexpectedly low threshold and large red-shift of the gain peak by comparing it to a state filling model with a substantial red-shift of the stimulated emission. Our results indicate the concept and advantage of bulk nanocrystals remains intact also in the infrared spectrum, indicating a large potential for integrated infrared light sources.

References:

[1] Park, YS., Roh, J., Diroll, B.T. et al. Colloidal quantum dot lasers. Nat Rev Mater 6, 382–401 (2021).

[2] Tanghe, I., Samoli, M., Wagner, I. et al. Optical gain and lasing from bulk cadmium sulfide nanocrystals through bandgap renormalization. Nat. Nanotechnol. 18, 1423–1429 (2023).

[3] Whitworth, G.L., Dalmases, M., Taghipour, N. et al. Solution-processed PbS quantum dot infrared laser with room- temperature tunable emission in the optical telecommunications window. Nat. Photon. 15, 738–742 (2021).

[4] G. L. Whitworth, C. Roda, M. Dalmases, N. Taghipour, M. Dosil, K. Nikolaidou, H. Dehghanpour, G. Konstantatos, Extended Short-Wave Infrared Colloidal Quantum Dot Lasers with Nanosecond Excitation. Adv. Mater. 2024, 2410207.

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