Superfluorescent pulsed emission from biexcitons in an ensemble of semiconductor quantum dots

Abstract

Picosecond time-resolved photoluminescence from biexcitons in CuCl quantum dots (QDs) embedded in a NaCl matrix has been measured using an optical Kerr gate method. Ultrafast pulsed emission from the biexciton states was observed for the first time, only under resonant two-photon excitation of biexcitons. This implies that complete population inversion between the biexciton and exciton states is necessary in order to trigger the pulsed emission. In addition, the nature of the dependence of the time profiles of the pulsed emission on the excitation intensity reveals that the peak intensity is directly proportional to the square of the number of excited QDs. We conclude that this phenomenon is caused by superfluorescence, that is, the cooperative spontaneous radiative decay of many isolated excited states coupled by a resonant electromagnetic wave. Such a phenomenon has been observed for the first time in an ensemble of semiconductor QDs in this study. The results presented in this paper show that it is possible to control the microscopic coherent dynamics of electronic excited states in a QD ensemble.

Biexcitonic superfluorescence from CuCl quantum dots under resonant two‐photon excitation

“…We recently reported superfluorescence from biexcitons in an ensemble of CuCl QDs under resonant twophoton excitation of biexcitons [16,17]. The observed superfluorescence PL band (which we termed the FM band) clearly exhibited pulse-shaped temporal profiles and the excitation density dependence of the peak intensity was consistent with superfluorescence.…”

“…The FM band (3.168 eV) appears as a short pulse at the delay time of 7.7 ps, then the M band (3.158 eV) appears and reaches a peak at a delay time of ~20 ps. In a previous report, we conclude that both the M and FM bands originate from the biexciton states; these bands disappear under a circularly polarized excitation pulse due to the polarization selection rule of biexciton under resonant excitation [17]. In particular, a compete population inversion between the biexciton and exciton states was found to be necessary to generate the FM band because it appeared only under resonant two-photon excitation of the biexcitons.…”

“…Figure 1 shows the excitation density dependence of the time-integrated PL spectra. The M band at 3.158 eV has been reported as a biexciton band [14][15][16][17][18][19]. In addition, a new PL band (denoted by FM) appeared on the higher energy side of the M band.…”

Superfluorescent Pulsed Emission from Biexcitons in an Ensemble of CuCl Quantum Dots

“…In addition, a pulsed emission denoted as FM was observed at the delay time of 3 ps before the rises of the M and BM bands [14,15]. The M, BM, and FM bands were not observed under the circularly polarized excitation pulse [15]. The M, BM, and FM bands were not observed under the circularly polarized excitation pulse [15].…”

“…An analysis of the time profiles of the FM band was previously reported [15]. The FM band had a pulsed shape.…”