Spectroscopy of optical gain in low threshold colloidal quantum dot laser media: Dominance of single-exciton states at room temperature

Kwangdong Roh, Joonhee Lee, Cuong Dang, Arto Nurmikko

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Experimental studies of amplified spontaneous emission (ASE) and lasing from various colloidal II-VI semiconductor nanocrystals have been used as inputs to several microscopic models for underlying optical gain, usually involving permutations of quantum confined multiple excitonic states. Here we focus on particular types of CdSe/ZnCdS and CdSe/ZnS/ZnCdS colloidal quantum dot (CQD) films and elucidate on the discovery of single-exciton states at the fundamental edge as a dominant mechanism for optical gain at room temperature. Pump-probe spectroscopic techniques enable us to measure the onset of gain at ensemble-average exciton occupancy per CQD, < N > = 0.6 and 0.7 for the two types of CQD films at room temperature. Time-resolved measurements, in turn, show how optical gain persists well into the time regime associated with spontaneous emission (nanoseconds), thus providing direct evidence for how the non-radiative Auger recombination processes (~100 ps) can be thwarted. In addition to benefits of the material assets of densely packed CQD films with high luminescence efficiency (quantum yield ~90%) and nanoparticle monodispersity therein, we propose that access to the single-exciton gain regime at room temperature requires a careful spectral balance between the lowest exciton absorption resonance and its corresponding red-shifted spontaneous emission maximum ("Stokes shift").

Original languageEnglish
Pages (from-to)3776-3786
Number of pages11
JournalOptical Materials Express
Volume6
Issue number12
DOIs
StatePublished - 2016

Bibliographical note

Funding Information:
The authors would like to thank QD Vision Inc. for providing the materials. We acknowledge financial support from the Department of Energy (Basic Energy Sciences) under grant DEFG02-07ER46387, National Science Foundation grant ECCS-1128331 and the Air Force Office of Scientific Research (AFOSR), and Quantum Metaphotonics and Metamaterials MURI (AFOSR Award No. FA9550-12-1-0488). C.D. thanks NTU start-up grant and AcRF Tier 1 grant RG70/15 from Ministry of Education.

Publisher Copyright:
© 2016 Optical Society of America.

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