The influence of the surrounding cavity on the efficiency of different types of polaritonic emitters of THz radiation has been analysed. It is demonstrated that THz lasing threshold in realistic structures cannot be achieved without a THz cavity, due to destruction of polaritons via excitonic Mott transition. Even modest values of cavity quality factor (not exceeding 50) provide significant quantum efficiency.

A system of equidistant polariton states interacting with a terahertz electromagnetic field are considered that are localized in a cavity for terahertz radiation. Accumulation of terahertz photons in the cavity, together with boson stimulation of the transitions between polariton levels, leads to intense radiative transitions between terahertz levels. A concept of double-boson stimulated transitions between polariton levels in the boson cascade laser is proposed. We study a possibility of using the boson cascade laser in generation of terahertz radiation. The system exhibits threshold dependence of the intensity of terahertz radiation on pumping. The quantum effectiveness of the boson cascade laser can exceed unity when pumping is performed above the threshold. The interaction of polaritons with the cavity leads to an increase in the threshold of pumping and a decrease in quantum effectiveness.

Hybrid nanostructures based on InGaN nanowires with decorated plasmonic silver nanoparticles are investigated in the present study. It is shown that plasmonic nanoparticles induce the redistribution of room temperature photoluminescence between short-wavelength and long-wavelength peaks of InGaN nanowires. It is defined that short-wavelength maxima decreased by 20%, whereas the long-wavelength maxima increased by 19%. We attribute this phenomenon to the energy transfer and enhancement between the coalesced part of the NWs with 10–13% In content and the tips above with an In content of about 20–23%. A proposed Fröhlich resonance model for silver NPs surrounded by a medium with refractive index of 2.45 and spread 0.1 explains the enhancement effect, whereas the decreasing of the short-wavelength peak is associated with the diffusion of charge carriers between the coalesced part of the NWs and the tips above.