Two-photon excitation of confined biexcitons in CuCl quantum dots

Ultrafast emission under two‐photon excitation of biexcitons in CuCl quantum dots

“…For the CuCl QDs, on the other hand, the two-photon absorption processes have been confirmed by photoluminescence (PL) excitation spectra of the biexciton. The biexciton PL intensity was decreased with circularly polarized excitation compared to the linearly one, which agree with the polarization selection rule for the lowest biexciton state with the total angular momentum J = 0 [11]. Furthermore, under two-photon excitation, a highly efficient and subsequently stable laser emission from the biexciton state was observed [12,13].…”

Temporal behavior of biexciton luminescence under two-photon excitation in CuCl quantum dots

“…The nominal concentration of CuCl was about 1 mol% and the effective mean radius of the QDs was $7 nm.The matrix crystals were parallelly cleaved into slabs with the thickness of about 0.5 mm.The samples were cooled down to 4 K in a He-flow cryostat and optically pumped by tunable laser pulses (2 ps pulse duration, 1 kHz repetition rate), obtained from an optical parametric amplifier (TOPAS, Quantronics) pumped by a regeneratively amplified Ti:Sapphire laser (Spitfire, Spectra-Physics). The excitation photon energy was tuned to the energy of resonant two-photon excitation of the biexcitons or the one-photon excitation of the excitons [5]. The sample was excited by the pump laser with an incident angle of 101 from the normal to the sample surface, and then photoluminescence (PL) spectra were observed in the normal direction to the sample surface and analyzed by a spectrometer (SpectraPro-500i, ACTON) with a charge coupled device.…”

“…Lasing from biexcitons (excitonic molecules) in QDs of less than 10 nm was observed in II-VI [3] and I-VII [4] compounds, in both of their works, the lasing was achieved under intense band-to-band excitation with high-Q optical cavity. On the other hand, in our previous work, we reported an efficient lasing of biexciton luminescence under two-photon resonant excitation of CuCl QDs buried inside NaCl single-crystalline matrix [5][6][7]. There, the lasing was achieved with a low-Q cavity formed by parallelly cleaved surfaces of NaCl matrix without any coating, and was highly efficient and stable without Auger ionization of QDs that becomes predominant under the intense one-photon excitation.…”

Size‐selective excitation of biexcitons in CuCl quantum dots under two‐photon resonant excitation

“…In CuCl QDs, the two-photon resonant excitation of the biexcitons was confirmed by examining the incident polarization dependence of the PL excitation spectra of the biexcitons in which the PL intensity was weaker for the circularly polarized excitation than that for the linearly polarized one. It is because the lowest state of the biexciton has the total angular momentum J = 0 [23]. However, the PL of the free excitons could not be observed at low temperatures since the bound exciton PL was dominant.…”