We study the light emission from quantum emitter and double metallic nanoshell hybrid systems. Quantum emitters act as local sources which transmit their light efficiently due to a double nanoshell near field. The double nanoshell consists a dielectric core and two outer nanoshells. The first nanoshell is made of a metal and the second spacer nanoshell is made of a dielectric material or human serum albumin. We have calculated the fluorescence emission for a quantum emitter-double nanoshell hybrid when it is injected in an animal or human body. Surface plasmon polariton resonances in the double nanoshell are calculated using Maxwell's equations in the quasi-static approximation and the fluorescence emission is evaluated using the density matrix method in the presence of dipole-dipole interactions. We have compared our theory with two fluorescence experiments in hybrid systems in which the quantum emitter is Indocyanine Green or infrared fluorescent molecules. The outer spacer nanoshell of double metallic nanoshells consist of silica and human serum albumin with variable thicknesses. Our theory explains the enhancement of fluorescence spectra in both experiments. We find that the thickness of the spacer nanoshell layer increases the enhancement when the fluorescence decreases. The enhancement of the fluorescence depends on the type of quantum emitter, spacer layer and double nanoshell. We also found that the peak of the fluorescence spectrum can be shifted by changing the shape and size of the nanoshell. The fluorescence spectra can be switched from one peak to two peaks by removing the degeneracy of excitonic states in the quantum emitter. Hence using these properties one can use these hybrids as sensing and switching devices for applications in medicine.

We developed a theory for the fluorescence (FL) for quantum emitter and double metallic nanoshell dimer hybrids using the density matrix method. The dimer is made from two identical double metallic nanoshells, which are made of a dielectric core, a gold metallic shell and a dielectric spacer layer. The quantum emitters are deposited on the surface of the spacer layers of the dimers due to the electrostatic absorptions. We consider that dimer hybrids are surrounded by biological cells. This can be achieved by injecting them into human or animal cells. The surface plasmon polaritons (SPP) are calculated for the dimer using Maxwell's equations in the static wave approximation. The calculated SPP energy agrees with experimental data from Zhai et al (2017 Plasmonics 12 263) for the dimer made from a silica core, a gold metallic nanoshell and a silica spacer layer. We have also obtained an analytical expression of the FL using the density matrix method. We compare our theory with FL experimental data from Zhai et al (2017 Plasmonics 12 263) where the FL spectrum was measured by varying the thickness of the spacer layer from 9 nm to 40 nm. A good agreement between theory and experiment is found. We have shown that the enhancement of the FL increases as the thickness of the spacer layer decreases. We have also found that the enhancement of the FL increases as the distance between the double metallic nanoshells in the dimer decreases. These are interesting findings which are consistent with the experiments of Zhai et al (2017 Plasmonics 12 263) and can be used to control the FL enhancement in the FL-based biomedical imaging and cancer treatment. These interesting findings may also be useful in the fabrication of nanosensors and nanoswitches for applications in medicine.

We have developed a theory for the photoluminescence and absorption coefficient in nanohybrids made of an ensemble of metallic nanoparticles and the core–shell quantum emitter. The core–shell quantum emitter is made of a quantum emitter core and a dielectric shell. When a probe laser light falls on metallic nanoparticles, electric dipoles are induced in the ensemble. Hence, these dipoles interact with each other via the dipole–dipole interaction. The surface plasmon polaritons are also present in metallic nanoparticles. Excitons in the quantum emitter interact with these surface plasmon polaritons and the dipole–dipole interaction electric fields. Using the quantum mechanical density matrix method, we have developed a theory for the photoluminescence quenching and enhancement, the nonradiative decay rate, and the absorption coefficient for the quantum emitter in the ensemble of metallic nanoparticles. We showed that the nonradiative energy loss is mainly due to the exciton coupling with the dipole–dipole interaction and it is responsible for the power loss in the quantum emitter. This in turn produces anomalous photoluminescence enhancement and quenching. We have compared our theory with experimental data of core–shell CdSe/ZnS quantum dots embedded in an ensemble of Au nanoparticles. A good agreement between theory and experiment is found. We showed that there are an energy shift and an enhancement in the absorption peak due to the dipole–dipole interaction. Finally, we showed that there is the anomalous quenching and enhancement in the photoluminescence spectrum of the CdSe/ZnS quantum dot embedded in the ensemble of Au nanoparticles. This phenomenon also occurs mainly due to the dipole–dipole interaction in the ensemble of Au nanoparticles. These are interesting results and can be used to fabricate nanosensors for applications in nanomedicine and nanotechnology.

The transport properties of phonons in a nanocomposite have been investigated in this paper. In our model, the nanocomposite consists of nanoparticles embedded in a host dielectric material. The phonon dispersion relation of the nanocomposite is characterized in terms of a defined phonon refractive index and a filling factor parameter. This phonon refractive index depends on its velocity whereas the filling factor is determined by the diameter of the nanoparticles. Consequently, at zero filling, only the host material is present. Our model calculations also include point defects such as impurities, vacancies and the mass and size variations of nanoparticles. The phonon conductivity is determined by employing the Kubo formulism. We also report our calculated results for the phonon relaxation rates due to point defects and boundaries scattering where the latter is due to phonons interacting with the surface boundaries of nanoparticles and the host material. The thermal conductivity, dispersion relation, velocity, density‐of‐states and relaxation rates of phonons are determined by the filling factor and phonon refractive indices of the nanoparticles. There is a good agreement between our numerical results and the data obtained experimentally for the conductivity of AlN‐polyimide nanocomposite. Our results also demonstrate that as the filling factor is increased the phonon conductivity also increases. Possible applications are new types of nanocomposites with variable thermal conductivity by adjusting the filling factor and refractive indices of the nanoparticle and host material. These nanocomposites may be important components in the fabrication of thermal nanodevices used for heating and cooling.

We have developed a theory for the photoluminescence of dimer nanohybrids and trimer nanohybrids using the density matrix method. These nanohybrids are made from identical double metallic nanoshells embedded in an ensemble of quantum emitters. We consider that they are immersed in medical, biological, and chemical solutions. The dipole−dipole interaction between quantum emitters in the ensemble is calculated using the mean-field approximation. The effect of the dipole−dipole interaction has been included in the formulation of the photoluminescence. We have compared our theory with the experimental data of the ensemble of quantum emitters (ZnCdSeS-QDs) doped in chloroform and aqueous solutions. A good agreement between theory and experiment is found. We showed that the dipole−dipole interaction is stronger in the chloroform solution than that in the aqueous solution. Surface plasmon polariton resonances and electric fields are calculated for the metallic dimer and trimer by solving the Maxwell equations in the static wave approximation. The calculated surface plasmon polariton resonances agree with experimental data for an Au dimer and an Au trimer. We compare our theory with the photoluminescence experimental data of nanohybrids made from the ensemble of ZnCdSeS-QDs and the Au dimer and Au trimer. It is shown that the dipole−dipole interaction plays an important role in understanding the photoluminescence. We found that the intensity of the photoluminescence in the Au trimer nanohybrid is slightly higher than that in the Au dimer nanohybrid. This is because the surface plasmon polariton electric field emitted by the Au trimer is slightly larger than the electric field emitted by the Au dimer. We also found that two competing physical mechanisms, namely, the quenching and the enhancement, play important roles in these experiments. We showed that the quenching is due to the nonradiative decay rate, whereas the enhancement is due to the dipole−dipole interaction and surface plasmon polariton electric fields. These interesting findings may be useful in the fabrication of nanosensors for medical, biological, and chemical applications.