Abstract: Read at NATURE website Excitons in semiconductors and insulators consist of fermionic subsystems, electrons and holes, whose attractive interaction facilitates bound quasiparticles with quasi-bosonic character. In the presence of a degenerate electron gas, such excitons dissociate due to free carrier screening. Despite their absence, we found pronounced emission traces in the below-band-edge region of bulk, germanium-doped GaN up to a temperature of 100 K, mimicking sharp spectral features at high free electron concentrations (3.4E19–8.9E19 cm−3). Our interpretation of the data suggests that a degenerate, three-dimensional electron gas stabilizes a novel class of quasiparticles, which we name collexons. These many-particle complexes are formed by exchange of electrons with the Fermi gas. The potential observation of collexons and their stabilization with rising doping concentration is enabled by high crystal quality due to the almost ideal substitution of host atoms with dopants.
C. Nenstiel, G. Callsen, F. Nippert, T. Kure, S. Schlichting, N. Jankowski, M. P. Hoffmann, A. Dadgar, S. Fritze, A. Krost, M. R. Wagner, A. Hoffmann & F. Bechstedt

Abstract: Contactless measurements of water temperature are utilized in a number of sciences, such as oceanography, climatology, and biology. Previously reported Raman spectroscopy techniques exploited the changes in the shapes of water Raman bands. Interpretation of these changes is difficult since these bands are composed of multiple lines, each influenced not only by temperature but also by pressure and salinity. This paper presents a proof-of-principal demonstration of a contactless technique which determines water temperature from the ratio of Stokes and anti-Stokes intensities of the water 180 cm1 Raman band. This ratio is not sensitive to pressure and salinity, allowing reliable determination of water temperature.
S. P. Nikitin, C. Manka, J. Grun, and J. Bowles

Abstract: The luminous efficiency and lifetime of plasma display panels (PDPs) are directly related to the performance of phosphors used in PDPs, thus higher efficiency, higher stability against high temperature processes and a long lifetime along with good color chromaticity against vacuum-ultraviolet (VUV) radiation are major concerns in selecting suitable phosphors for PDPs. In the same pursuit, we have developed the nano-sized (15–40 nm) BAM:Eu2+, YAG:Tb3+ and YAG:Eu3+ as blue, green and red phosphors and studied their luminescence properties under VUV excitations. In BAM:Eu2+, the 5d-excitation of Eu2+ ions are found strongly dependent on the crystal field strength and Eu2+ occupy lattice ‘sites I’ by substituting Ba2+ ions. Whereas, in YAG:Tb3+, the observed green luminescence is assigned to 5D4?7Fj transitions (j = 3–6) due to electric dipole–dipole interaction, while, YAG:Eu3+ shows strong red luminescence corresponding to 5D0?7F2 transition. Time evolution studies along with decay time calculations are further employed to verify the sustainable emission without quenching.
Prashant K. Sharma, Ranu K. Dutta, Avinash C. Pandey

Abstract: Porous silicon samples have been prepared from p-type single-crystal silicon <100> by a galvanostatic and an open-circuit etch in 50% HF. The materials display bright red-orange room-temperature photoluminescence (PL) in air and toluene solution. Infrared measurements show that the porous silicon surface is partially oxidized. Exposure to anthracene (An) or 10-methylphenothiazine (MPTZ) results in dynamic quenching of the material's excited state(s). Nanosecond time-resolved PL decays are complex and wavelength dependent, with average lifetimes in neat toluene of 0.3-16 µs. Quenching by An and MPTZ is more efficient and rapid at short observation wavelengths. The steady-state and time-resolved quenching data are well fit to the Stern-Volmer model. The PL decays are well described by a skewed distribution of recombination rates.
Minh C. Ko and Gerald J. Meyer

Abstract: Discussed are the photoluminescence properties of combustion synthesized red and green emitting borate phosphors—YBO3 : Eu3+, BaZr(BO3)2 : Eu3+, YCaBO4 : Eu3+, YAl3(BO3)4 : Eu3+, YAl3(BO3)4 : Tb3+, LaBaB9O16 : Tb3+, LaBaB9O16 : (Ce3+,Tb3+), and Na3La2(BO3)3 : Tb3+-promising for use in plasma display panels and mercury-free fluorescent lamps.
P. A. Nagpure, S. K. Omanwar

Abstract: Coherent anti-Stokes Raman scattering (CARS) with femtosecond interaction pulses has become a popular and powerful spectroscopic method. Non-resonant background is one of the most limiting factors for implementing this method more widely. We propose a new approach that suppresses the non-resonant background contribution to the measured signal in CARS spectroscopy while simultaneously yielding high spectral resolution. The method is based on femtosecond pulse shaping of probe, Stokes and pump beams. Destructive interference suppresses the non-resonant background, resulting only in the resonant contribution being detected.
Stanislav O. Konorov, Michael W. Blades and Robin F. B. Turner

Abstract: We investigate the possibility of implementing coherent anti-Stokes Raman spectroscopy (CARS) with a single laser beam passed through a one-dimensional scattering object. The effect of the random scattering is emulated by shaping the laser pulses with a spectral mask corresponding to the transmission spectrum of a random layered medium. Raman resonances are retrieved through correlation analysis of the CARS spectrum. We study the effect of the scattering parameters on the resolution of the method, and show that improvement of the spectroscopic sensitivity can be achieved by compensating the phase distortions introduced by the scatterer
T.M. Drane, J.W. Hepburn and V. Milner

Abstract: Visible light extinction was measured in a series of nitrogen-diluted, ethylene/air, non-premixed flames and this data was used to determine the optical band gap, OBG, as a function of flame position. Collimated light from a supercontinuum source is telescopically expanded and refocused to match the f – number of a dispersing monochromator. The dispersed light is split into a power metering channel and a channel that is periscoped and focused into the flame. The transmitted light is then recollimated and focussed onto a silicon photodiode detector. After tomographic reconstruction of the radial extinction field, the OBG was derived from the near-edge absorption feature using Tauc/Davis–Mott analysis. A slight evolution in OBG was observed throughout all flame systems with a consistent range of OBG observed between approximately 1.85 eV and 2.35 eV. Averaging over all positions the mean OBG was approximately 2.09 eV for all flame systems. Comparing these results to previously published computational results relating calculated HOMO–LUMO gaps for a variety of D2h PAH molecules to the number of aromatic rings in the structure, showed that the observed optical band gap is consistent with a PAH of about 14 rings or a conjugation length of 0.97 nm. This work provides experimental support to the model of soot formation where the transition from chemical to physical growth starts at a modest molecular size; about the size of circumpyrene.
Erin M. Adkinsa and J. Houston Miller. DOI: 10.1039/C4CP04452E