We report the direct and unambiguous evidence of the existenceof inner semiconducting tube (iSCT) photoluminescence (PL)from measurements performed on four individual free-standingindex-identified double-walled carbon nanotubes (DWNTs).Based on thorough Rayleigh scattering, Raman scattering andPL experiments, we are able to demonstrate that the iSCT PLis observed with a quantum yield estimated as a few 10−6 independentlyof the semiconducting or metallic nature of theouter tube. This result is mainly attributed to ultrafast excitontransfer from inner to outer tube. Furthermore, by carryingout PL excitation experiments on the (14,1)@(15,12) DWNT,we show that the iSCT PL can be detected through the opticalexcitation of the outer tube (Fig. 1) indicating that the excitontransfer can also occur in the opposite way.

We report the direct and unambiguous evidence of the existence of inner semiconducting tube (iSCT) photoluminescence (PL) from measurements performed on four individual free-standing index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering and PL experiments, we are able to demonstrate that the iSCT PL is observed with a quantum yield esti-mated as a few 10-6 independently of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14,1)@(15,12) DWNT, we show that the iSCT PL can be detected through the optical excitation of the outer tube (Figure 1) indicating that the exciton transfer can also occur in the opposite way.

Abstract-Biochemical detection applications and on-chip optical interconnects are examples of the useful applications considered for integrated photonic platforms dedicated to the UV and visible spectral range. This achievement requires the realization of efficient and compact microlaser sources that can be coupled to optical waveguides and are compatible with photonic circuitry. We develop a cost-effective practical approach relying on the controlled growth of thin AlN buffer layers on silicon substrates, followed by the growth of multiple quantum wells (MQW) GaN/AlN (for UV operation), or InGaN/GaN MQWs (for violet and blue operation) with a high radiative efficiency up to T=300K. This unique Nitride-on-Silicon platform could be released into a membrane by the selective under-etching of the silicon substrate.We present a series of microdisk lasers operating at room temperature under pulsed optical excitation over a broad spectral range extending from 275nm to 470nm. All microdisks present a Q factor above 1000 and reach 4000 in the best resonators. We are able to investigate the gain threshold of the different active layers. The microlasers operate under pulsed optical excitation, and the lasing threshold is reduced by a factor 10 from deep-UV GaN/AlN microdisks to the violet InGaN/GaN ones. This work allows us to expect a variety of integrated photonics applications, including for example multi-color integrated laser sources: we demonstrate here the versatility of this nitride-on-silicon platform, and the first realization on this platform of efficient active layers for a tunable lasing action over a 200nm broad UV to visible spectral range. [1,2].Acknowledgements: The authors acknowledge support from the projects GANEX (ANR-11-LABX-0014) and QUANONIC (ANR-13-BS10-0010). GANEX belongs to the public funded 'Investissements d'Avenir' program managed by the French ANR agency. This work was also partly supported by the RENATECH network.REFERENCES1.Sellés et al., APL 109, 231101 (2016)2.Sci. Rep. 6, 21650 (2016)

The polariton emission in a microcavity is usually measured from the surface, and little is known about the actual role of guided modes below the light cone in air, that can couple to the exciton transition, collect part of the emission and contribute to polariton losses. In this work we investigate a ZnO planar microcavity with mesas. The emission of the guided modes is observed at the mesa’s edge, together with the vertical emission. The microcavity operates as a polariton laser under pulsed optical pumping [1].The spectra collected under the excitation spot and at the mesa’s edge are very different, as shown on figure 1a. The vertical emission is dominated by the lower polariton branch (LPB) associated to the cavity mode whereas the edge emission forms a broad peak modulated by fringes which spacing decreases as the spot moves away from the edge. While these fringes could indicate Fabry-Perot oscillations of polaritons propagating in-plane, in analogy with radiative polaritons in GaAs microcavity wires [2], a careful analysis shows that they are the signature of beatings between 5 to 10 guided modes, without being necessary to invoke multiple reflections. These modes have a large attenuation length of 27 µm, intermediate between the propagation length of LPB polaritons (a few µm in a ZnO microcavity [3]) and the one of waveguide polaritons (100µm in a GaN microcavity [4]).Under pulsed optical pumping, the guided modes are strongly excited. They form leaky modes for the excitonic reservoir, as well as for the LPB polaritons themselves. Most interestingly, when the vertical microcavity displays polariton lasing, the polariton laser emission feeds the guided modes, which then cascade in energy (Fig. 1b,c).This work evidences therefore that the threshold of the polariton laser in conventional vertical microcavities is increased due to the existence of usually hidden guided modes, that can deplete the exciton reservoir and collect resonantly scattered light from the lasing LPB mode.