Materials
Experimental and theoretical work carried out by many leading physicists, including Albert Einstein, at the beginning of the 20th century, changed the way we understand the nature of light. It was shown that light consists of a fundamental particle, called a photon, which can be seen as a packet of light or radiation. While light is commonly associated with the visible colours seen in everyday life, it consists of a wide range of frequencies divided into different regions, for example, X-ray radiation, Ultraviolet radiation, Visible light and Infrared radiation, all part of the electromagnetic spectrum. The various regions of the electromagnetic spectrum will interact with matter in significantly different ways. The main interaction of light with matter consists of, energetic ejection or excitation of core electrons, excitation of molecular and atomic valence electrons, molecular electron excitation, molecular vibration or rotation. The outcome of these interactions with matter leads to transmission, reflection or an absorption process that may lead to a re-emission of light. For example, the interaction of visible light and leaves on vegetation leads to both a reflection (typically a green colour) and absorption due to chlorophyll, a common molecule found in plants. By using these interactions of light and matter, it is possible to probe the atomic and molecular structure of matter and falls within the field of spectroscopy.
Nano Diamonds
Nanodiamonds or diamond nanoparticles, are diamonds with a size below 1 micrometre. They can be produced by impact events such as an explosion or meteoritic impacts. Because of their inexpensive, large-scale synthesis, potential for surface functionalization, and high biocompatibility, nanodiamonds are widely investigated as a potential material in biological and electronic applications and quantum engineering.
Ideal diamond is a wide band-gap semiconductor with indirect energy gap of 5.45 eV and direct gap at Γ point of 7.3 eV at room temperature. Deep UV excitation assures excitation of not only ground electronic state but also all defect- and impurity-related bands and sub-bands present inside the band-gap. In an indirect gap crystal (Si, Ge, diamond…) the radiative recombination of photo-excited electrons from conduction band to valence band by means of light emission is a process of extremely low probability. The most probable scenario in an optically-excited crystal is a cascade of phonon-related non-radiative recombination events, combined with an excitation of optically-active impurities or defects levels (usually visible and IR fluorescence). The most common impurity levels and bands in diamond are nitrogen donor (1.7 eV), boron acceptor (0.37 eV), phosphorous donor (0.6 eV), and Sulphur donor (0.39-0.52 eV).

Nanolasers
The applications of (nano)lasers are numerous and extremely varied. It is easy to find coherent light emitters in medicine, food science, manufacturing companies, military sector and research. III-V materials possess high gain value, direct band gap, and easy band gap tunability by varying the alloy component. The major problem of III-V materials growth on silicon is the lattice mismatch at the interface, which produces dislocation and poor performance. In III-V semiconductor nanowires (NWs) and nanopillars (NPs), the lattice mismatch can be fully relaxed over a small number of monolayers because of its small footprint. Moreover, NWs/NPs offer significant potential for nanoscale laser source due to the quasi-one-dimensional structure, which facilitates a natural Fabry-Perot resonator cavity and optical gain medium simultaneously.
In CAPPA, time-resolved photoluminescence (TRPL) measurements were performed on molecular-beam epitaxy (MBE) grown AlGaAs/GaAs nanolasers. The samples were excited using a Ti:Sapphire pulsed laser emitting 780 nm, 200fs pulses with a repetition rate of 80MHz. Streak images were recorded with the Hamamatsu streak camera. The photoluminescence peak was seen to red-shift over time because of carrier contrentation influence on material refractive index (Figs. 1 and 2).

Nano Letters, 17, 3465-3470, 2017