Controlling the way light interacts with material excitations is at the heart of cavity quantum electrodynamics (QED). In the strong-coupling regime, quantum emitters in a microresonator absorb and spontaneously re-emit a photon many times before dissipation becomes effective, giving rise to mixed light-matter eigenmodes. Recent experiments in semiconductor microcavities reached a new limit of ultrastrong coupling, where photon exchange occurs on timescales comparable to the oscillation period of light. In this limit, ultrafast modulation of the coupling strength has been suggested to lead to unconventional QED phenomena. Although sophisticated light-matter coupling has been achieved in all three spatial dimensions, control in the fourth dimension, time, is little developed. Here we use a quantum-well waveguide structure to optically tune light-matter interaction from weak to ultrastrong and turn on maximum coupling within less than one cycle of light. In this regime, a class of extremely non-adiabatic phenomena becomes observable. In particular, we directly monitor how a coherent photon population converts to cavity polaritons during abrupt switching. This system forms a promising laboratory in which to study novel sub-cycle QED effects and represents an efficient room-temperature switching device operating at unprecedented speed.

In a microcavity, light-matter coupling is quantified by the vacuum-Rabi frequency Omega_R. When Omega_R is larger than radiative and nonradiative loss rates, the system eigenstates (polaritons) are linear superposition of photonic and electronic excitations, a condition actively investigated in diverse physical implementations. Recently, a quantum electrodynamic regime (ultrastrong coupling) was predicted when Omega_R becomes comparable to the transition frequency. Here we report signatures of this regime in a quantum-well intersubband microcavity. Measuring the cavity-polariton dispersion in a room-temperature linear optical experiment, we directly observe the antiresonant light-matter coupling and the photon-energy renormalization of the vacuum field

Herein we report the observation of room-temperature phosphorescence from carbon dots (CDs) embedded in a silica gel matrix. The precursors used in the synthesis (malonic acid and ethylene diamine) were chosen to have the surface of the CDs rich in C[double bond, length as m-dash]O and C[double bond, length as m-dash]N functionalities. The CDs in an aqueous dispersion exhibit an intense blue fluorescence and upon incorporation into silica gel demonstrate a green after-glow, which is visible even to the naked eye. The phosphorescence measurements indicated that the life-time of phosphorescence emission is about 1.8 s, under 380 nm excitation, which is the highest magnitude reported for CDs in solid-state matrices. Moreover, the 1931 CIE color parameters corresponding to the phosphorescence emission are in the white gamut region of the chromaticity diagram.

We demonstrate the external control of the coupling between the intersubband transition and the photonic mode of a GaAs∕AlGaAs microcavity with multiple quantum wells embedded. By electrical gating, the charge density in the wells can be lowered, thereby quenching the intersubband polaritons and reverting the system to uncoupled excitations. The angle-dependent reflectance measurements are in good agreement with theoretical calculations performed in the transfer matrix formalism. The experiment shows the prospects offered by intersubband microcavities through manipulation of the system ground state.

The single-step synthesis of white-light-emitting carbon dots (CDs) through a green, facile and cheap electrochemical route by using graphite rods as the carbon source is reported. Under UV excitation, the aqueous dispersion of as-synthesised CDs exhibit broad-band emission, which covers a significant fraction of the visible spectrum, owing to the heterogeneity in particle size and surface functional groups. The CDs were further explored for their potential as UV-to-visible colour convertors under remote-phosphor technology by capping a λ=365 nm UV light-emitting diode (LED) chip with CD-loaded poly(methyl methacrylate) to obtain the following colour parameters: Commission Internationale de l'Eclairage chromaticity coordinates (0.35, 0.37), colour rendering index (88) and correlated colour temperature (4802 K).

The authors report the external control of the polariton ground state by manipulating the coupling between the intersubband transition and the photonic mode of a GaAs/ AlGaAs microcavity. The vacuum-field Rabi splitting is varied by means of charge transfer between the energetically-aligned ground subbands of asymmetric tunnel-coupled quantum wells. The authors propose the use of this structure concept for implementing ultrafast modulation of intersubband polaritons.

We report a skeleton key platform for surface enhanced Raman spectroscopy (SERS) based biosensor, utilizing ordered arrays of Si nanopillars (SiNPLs) with plasmonic silver nanoparticles (AgNPs). The optimized SiNPLs based SERS (SiNPLs-SERS) sensor exhibited high enhancement factor (EF) of 2.4 × 10 8 for thiophenol with sensitivity down to 10 −13 M of R6G molecules. The ordered array of SiNPLs stabilizes the distribution of AgNPs along with the light trapping properties, which resulted in high EF and excellent reproducibility. The uniformity in the arrangement of AgNPs makes a single SiNPLs-SERS substrate to work for all types of biomolecules such as positively and negatively charged proteins, hydrophobic proteins, cells and dyes, etc. The experiments conducted on differently charged proteins, amyloid beta (the protein responsible for alzheimers), E. coli cells, healthy and malaria infected RBCs provide a proof of concept for employing universal SiNPLs-SERS substrate for trace biomolecule detection. The FDTD simulations substantiate the superior performance of the sensor achieved by the tremendous increase in the hotspot distribution compared to the bare Si sensor.

We report on the coupling of optical transitions between excited conduction subbands in GaAs∕AlGaAs heterostructures with the resonant photonic mode of a semiconductor microcavity. The coupling is found to increase with temperature, owing to the thermal excitation of carriers from the ground subband and, thanks to the large dipole-matrix element of the excited-state transition, a record splitting of 60meV is shown in the room-temperature reflectance. The importance of translating the angle-dependent spectra into energy-wavevector dispersion when the coupling is so large is highlighted, and a theoretical fitting procedure is used to extract the value of the vacuum-field Rabi energy.