Anisotropic Radiation in Heterostructured “Emitter in a Cavity” Nanowire

Tailorable synthesis of axially heterostructured epitaxial nanowires (NWs) with a proper choice of materials allows for the fabrication of novel photonic devices, such as a nanoemitter in the resonant cavity. An example of the structure is a GaP nanowire with ternary GaPAs insertions in the form of nano-sized discs studied in this work. With the use of the micro-photoluminescence technique and numerical calculations, we experimentally and theoretically study photoluminescence emission in individual heterostructured NWs. Due to the high refractive index and near-zero absorption through the emission band, the photoluminescence signal tends to couple into the nanowire cavity acting as a Fabry–Perot resonator, while weak radiation propagating perpendicular to the nanowire axis is registered in the vicinity of each nano-sized disc. Thus, within the heterostructured nanowire, both amplitude and spectrally anisotropic photoluminescent signals can be achieved. Numerical modeling of the nanowire with insertions emitting in infrared demonstrates a decay in the emission directivity and simultaneous rise of the emitters coupling with an increase in the wavelength. The emergence of modulated and non-modulated radiation is discussed, and possible nanophotonic applications are considered.

Free and self-trapped exciton emission in perovskite CsPbBr3 microcrystals

A broad STE emission band together with a FE emission was found at low temperature in a CsPbBr3 microcrystal sample prepared by CVD method.

Reference UVC LED Source

A compact reference UVC source based on commercially available LED has been developed. The article presents the design and results of the study of the optical characteristics of the radiation of the reference UVC LED source. The source provides a power density of radiation up to 400 μW/cm2 on area of 3×3 mm with inhomogeneity of 1.5 %.The emission band of a source with a maximum of 265 nm is predominantly 97 % in the UV-C spectrum region, and a small part of it is inUV-B and UV-A regions, 2.7 % and 0.3 %, respectively. The use of ComboSource for laser diodes allowed to precisionally stabilize the injection current and temperature of the LED. It is shown that overheating of the active region of the selected UV LED is only 10°C - 25°C at the recommended injection currents due to the peculiarities of its design. This results in a low degradation rate of the UV LED. Possible ways to improve the characteristics of the reference UVCsource are discussed.

Synthesis and Photoluminescence Properties of Eu3+-Doped Na2YMg2V3O12: A Novel Red-Emitting Phosphor for White-Light-Emitting Diodes

The fabrication and luminescent properties of novel Na2YMg2V3O12:Eu3+ phosphors produced by conventional solid-state reactions were investigated. Self-activated emission of the Na2YMg2V3O12 host produces a broad emission band ranging from 400 to 700 nm with a maximum peak at 530 nm, ascribed to the charge transfer in the (VO4)3− groups. Excitation with near-UV (365 nm) light causes the Na2YMg2V3O12:Eu3+ phosphors to emit bright red light, including both the broad emission band of the (VO4)3− groups and the sharp emission peaks of Eu3+ ions. At a quenching concentration of 0.03 mol, the Eu3+ ion emission peaks were located at 597, 613, 654 and 710 nm. As-prepared Na2YMg2V3O12:Eu3+ phosphors also exhibited stable emission at high temperatures. Furthermore, a designed and packaged white-light-emitting diode (WLED) lamp, including the obtained phosphors, commercial (Ba,Sr)2SiO4:Eu2+ green phosphors, BaMgAl10O17:Eu2+ blue phosphors and a near-ultraviolet (n-UV) chip, emitted bright white light with a good chromaticity coordinate of (0.3068, 0.3491), a satisfactory colour rendering index of 88.20 and a properly correlated colour temperature of 4460.52 K. These results indicate the potential of this Na2YMg2V3O12:Eu3+ phosphor as a red-emitting phosphor for solid-state illumination.

Synthesis and Optical Characterizations of Yb3+: CaxSr1−xF2 Transparent Ceramics

In this study, 3 at.% Yb3+: CaxSr1−xF2 nanopowders were synthesized via the chemical co-precipitation method. Highly transparent 3 at.% Yb3+: CaxSr1−xF2 ceramics with various CaF2 concentrations were fabricated by hot-pressed sintering. The 3 at.% Yb3+: CaxSr1−xF2 nanopowders exhibited a spherical shape with slight agglomeration, and their particle size ranged from 26 nm to 36 nm. With an increase of the CaF2 concentration, the peak shape changed significantly and the width of the emission band increased inhomogeneously. The minimal fluorescence lifetime at the wavelength of 1011 nm of 3 at.% Yb3+: CaxSr1−xF2 transparent ceramics with various CaF2 concentrations was higher than 3.25 ms, which was longer than that of the 3 at.% Yb3+: CaF2 (2.6 ms) and the 3 at.% Yb3+: SrF2 (3.22 ms) reported in previous literature. The results indicate that incorporating Ca2+ ions into the SrF2 is an effective method to modulate the optical properties of transparent ceramics.

Vibrational and Photoluminescence Properties of Composites Based on Double-Walled Carbon Nanotubes, Poly(o-phenylenediamine) and Poly(ethylene oxide)

Chemical polymerization of o-phenylenediamine (OPD) in the presence of poly(ethylene oxide), double-wall carbon nanotubes (DWNTs) and ferric chloride is carried out in order to obtain composites based on the poly(o-phenylenediamine)-poly(ethylene oxide) (POPD-PEO) fibres covered and interconnected with DWNTs. Vibrational and photoluminescence properties of these composite materials as well as their morphologies are shown by infrared (IR) spectroscopy, Raman scattering, photoluminescence (PL) and scanning electron microscopy (SEM). An adsorption of DWNTs onto the POPD rods surface in the absence and in the presence of PEO is highlighted by SEM. The vibrational changes reported by Raman scattering and IR spectroscopy prove a covalent functionalization of DWNTs with the macromolecular compound POPD which is doped with FeCl−4 ions. New hydrogen bonds are generated between POPD covalently functionalized DWNTs and hydroxyl groups of PEO according to IR spectroscopic studies. The two macromolecular compounds, POPD and POPD-PEO, show a complex emission band with maxima at 572 and 566 nm, having a shoulder at 667 nm. A significant change in the profile of the PL bands of POPD and POPD-PEO is induced in the DWNTs presence. We show that DWNTs induce (i) a diminution in the POPD PL band intensity peaked between 525–600 nm simultaneous with the increase in the intensity of the PL band situated in the 600–800 nm spectral range and (ii) an enhancement process of the emission band localized in the 475–800 nm spectral range in the case of POPD-PEO.