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

Abstract

Here, 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, = 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”).

Authors:

Roh, Kwangdong ^[1]; Lee, Joonhee ^[2]; Dang, Cuong ^[3]; Nurmikko, Arto ^[2]

---

+ Show Author Affiliations

1. Brown Univ., Providence, RI (United States); Princeton Univ., Princeton, NJ (United States)
2. Brown Univ., Providence, RI (United States)
3. Nanyang Technological Univ. (Sinagpore)

Publication Date:

Wed Nov 09 00:00:00 EST 2016

Research Org.:

Brown Univ., Providence, RI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1466783

Grant/Contract Number:  

FG02-07ER46387

Resource Type:

Accepted Manuscript

Journal Name:

Optical Materials Express

Additional Journal Information:

Journal Volume: 6; Journal Issue: 12; Journal ID: ISSN 2159-3930

Publisher:

Optical Society of America (OSA)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE