In this work, we demonstrate semiconductor quantum dots weakly coupled to photonic crystal cavity modes operating in
the visible spectrum. We present the design, fabrication and characterization of two dimensional photonic crystal cavities
in GaInP and measure quality factors in excess of 7,500. We demonstrate control over the spontaneous emission rate of
InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode
we observe a Purcell enhancement of ~8.
We have experimentally observed the time evolution of the photoluminescence spectra of InGaN/GaN quantum wells with widths 3 and 4 nm in response to pulsed excitation at room temperature. We find that for both well widths the time evolution of the energy-integrated photoluminescence increases initially then decays and the spectrum displays a blue shift of the peak energy which then reverses. Through an iterative simulation of the carrier density, piezoelectric field and radiative recombination rate we calculate the behavior of these quantum well systems and find good agreement with the experimental data. The internal field present in the InGaN/GaN system is screened as carrier density increases, which combined with band filling and coulomb interactions result in a blue shift as the system is pumped and as recombination of the carriers occur a red shift is simulated. Although screening of the internal fields occurs our calculations show that at laser threshold there is still a large internal field present, 1.0 MVcm<sup>-1</sup>, which is 75 % of the unscreened value.
We report systematic measurements of the evolution of the emission characteristics of PFO whilst undergoing photo-oxidation. Pure PFO and highly diluted PFO/polystyrene blended films were prepared for the studies by spin-coating. Each film was oxidized by exposure to the 351 nm line of a cw Ar<sup>+</sup> laser. Both the kinetics of the various spectral components and the photoluminescence intensity for each film was monitored as a function of oxidation time and their respective behaviors were compared. Our results demonstrate that there is a strong tendency for singlet intrachain excitons initially created on pristine PFO segments to migrate to the fluorenone moieties produced by photo-oxidation. However, we conclusively show that emission from states localized at these defect sites cannot account for the appearance of the broad green emission band (g-band) that is well-known to occur in degraded polyfluorenes. Instead, it is shown that the g-band must emanate from interchain states that are formed after energy has been transferred to the fluorenone moieties (either via energy transfer form non-defective PFO segments or by direct excitation).
Conference Committee Involvement (1)
Quantum Dots, Nanostructures, and Quantum Materials: Growth, Characterization, and Modeling XVII
5 February 2020 | San Francisco, California, United States