Hexagonal boron nitride (h-BN) is an attractive van der Waals material for studying fluorescent defects due to its large bandgap. In this work, we demonstrate enhanced pink color due to neutron irradiation and perform electron paramagnetic resonance (EPR) measurements. The new point defects are tentatively assigned to doubly-occupied nitrogen vacancies with (S = 1) and a zero-field splitting (D = 1.2 GHz). These defects are associated with a broad visible optical absorption band and near infrared photoluminescence band centered at ~ 490 nm and 820 nm, respectively. The EPR signal intensities are strongly affected by thermal treatments in temperature range between 600 to 800ºC, where also the irradiation-induced pink color is lost. Our results are important for understanding of point defects in h-BN and their deployment for quantum and integrated photonic applications.

No abstract

No abstract

We demonstrate that hybrid systems of porphyrins and chirality enriched (6,5) single-walled carbon nanotubes (E-SWCNTs) are better candidates for photodynamic therapy (PDT) than their components alone. Surprisingly, the E-SWCNTs act as optical absorption enhancers to the porphyrins increasing the oxygen singlet production when illuminated by a light source with energy higher than the E-SWCNT gap plus the equivalent in energy of an E-SWCNT phonon. The phenomenon is explained based on energy transfer from the E-SWCNT to the porphyrin which finally transfers it to the oxygen molecule. The large optical absorption cross section of E-SWCNT and the resonance of the porphyrin to the oxygen singlet–triplet transition are responsible for the synergistic effect.

Semiconductor nanomembranes are promising systems for many applications, since the band structure of a given material can be tailored to achieve specific configurations, which are not feasible by conventional growth procedures on rigid substrates. Here we show that optically active III–V membranes containing InAs quantum dots exhibit a pronounced photoluminescence enhancement with respect to equivalent systems grown on top of flat substrates. The effect is explained by the formation of carrier depletion regions symmetrically located with respect to the optically active layer. This leads to the filling of excited states of the quantum dots and the overall spectra are enhanced at higher energies. Changes on the strain field that are expected to lead to a red-shift of the quantum dot emission play a reduced role in the final emission spectra in comparison with the depletion effects. These effects can be considered as another degree of freedom and a key ingredient for band engineering of extremely thin semiconductor membranes.