Free-space and underwater GHz data transmission using AlGaInN laser diode technology

Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence and security applications; in particular for free space laser communication. Conventional underwater communication is done acoustically with very slow data rates, short reach, and vulnurable for interception. AlGaInN blue-green laser diode technology allows the possibility of both airbourne links and underwater telecom that operate at very fast data rates (GHz), long reach (100’s of metres underwater) and can also be quantum encrypted. The latest developments in AlGaInN laser diode technology are reviewed for defence and security applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported in free-space and underwate

Indirect excitation of Eu3+ in GaN codoped with Mg and Eu

Temperature-dependent Eu3+ luminescence spectra in GaN(Mg):Eu can be assigned to, at least, two distinct Eu3+ centres, denoted by Eu0 and Eu1. The splitting energy levels of the 7FJ (J=1,2) multiplets for the Eu0 and Eu1 centres have been calculated using the equivalent operator Hamiltonian for C3v crystal field with the addition of an odd parity distortion

Acceptor state anchoring in gallium nitride

The dual nature of the magnesium acceptor in gallium nitride results in dynamic defect complexes. Europium spectator ions reveal switching between two spectrally unique metastable centres, each corresponding to a particular acceptor state. By ion co-implantation of europium and oxygen into GaN(Mg), we produce, in addition, an anchored state system. In doing so we create an abundance of previously unidentified stable centres which we denote as "Eu0(Ox)". We introduce a microscopic model for these centres with oxygen substituting for nitrogen in the bridging site

Crystalfield symmetries of luminescent Eu3+ centers in GaN : the importance of the 5D0 to 7F1 transition

Eu-doped GaN is a promising material with potential application not only in optoelectronics but also in magneto-optical and quantum optical devices ‘beyond the light emitting diode’. Its interesting spectroscopy is unfortunately complicated by spectral overlaps due to ‘site multiplicity’, the existence in a given sample of multiple composite centers in which Eu ions associate with intrinsic or extrinsic defects. We show here that elementary crystalfield analysis of the 5D0 to 7F1 transition can critically distinguish such sites. Hence, we find that the center involved in the hysteretic photochromic switching (HPS) observed in GaN(Mg):Eu, proposed as the basis of a new solid state qubit material, is not in fact Eu1, as previously reported, but a related defect, Eu1(Mg). Furthermore, the decomposition of the crystalfield distortions of Eu0, Eu1(Mg) and Eu1 into axial and non-axial components strongly suggests reasonable microscopic models for the defects themselves

Luminescence of Eu3+ in GaN(Mg, Eu): transitions from the 5D1 level

Eu-doped GaN(Mg) exemplifies hysteretic photochromic switching between two configurations, Eu0 and Eu1(Mg), of the same photoluminescent defect. Using above bandgap excitation, we studied the temperature dependence of photoluminescence (TDPL) of transitions from the excited 5D1 level of Eu3+ for both configurations of this defect. During sample cooling, 5D1→7F0,1,2 transitions of Eu0 manifest themselves at temperatures below ~200 K, while those of Eu1(Mg) appear only during switching. The observed line positions verify crystal field energies of the 7F0,1,2 levels. TDPL profiles of 5D1→7F1 and 5D0→7FJ transitions of Eu0 show an onset of observable emission from the 5D1 level coincident with the previously observed, but hitherto unexplained, decrease in the intensity of its 5D0→7FJ emission on cooling below 200 K. Hence the 5D0→7FJ TDPL anomaly signals a back-up of 5D1 population due to a reduction in phonon-assisted relaxation between 5D1 and 5D0 levels at lower temperatures. We discuss this surprising result in the light of temperature-dependent transient luminescence measurements of Eu0

Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure

In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260–4000 K

Eu-Mg defects and donor-acceptor pairs in GaN : photodissociation and the excitation transfer problem

We have investigated temperature-dependent photoluminescence (TDPL) profiles of Eu3+ ions implanted in an HVPE-grown bulk GaN sample doped with Mg and of donor-acceptor pairs (DAP) involving the shallow Mg acceptor in GaN(Mg) (unimplanted) and GaN(Mg):Eu samples. Below 125 K, the TDPL of Eu3+ in GaN(Mg):Eu correlates with that of the DAP. Below 75 K, the intensity of Eu3+ emission saturates, indicating a limitation of the numbers of Eu-Mg defects available to receive excitation transferred from the host, while the DAP continues to increase, albeit more slowly in the implanted than the unimplanted sample. Prolonged exposure to UV light at low temperature results in the photodissociation of Eu-Mg defects, in their Eu1(Mg) configuration, with a corresponding increase in shallow DAP emission and the emergence of emission from unassociated EuGa (Eu2) defects

Assessment indices of barns with a varied maintenance system of dairy cows

Celem pracy było wyodrębnienie nowych wskaźników oceny budynków inwentarskich dla bydła mlecznego ze szczególnym uwzględnieniem ich technicznego wyposażenia. Zakresem pracy objęto obory z uwięziowym i wolnostanowiskowym systemem utrzymania, zróżnicowane pod względem pogłowia zwierząt w stadach. W opracowanym formularzu badawczym zestawiono zbiór podstawowych informacji na temat warunków produkcji bydła w poszczególnych obiektach. W trakcie bezpośrednich wizyt badawczych w gospodarstwach okazało się, że w oborach zaobserwowano nowe elementy, które wykorzystano do zaproponowania porównawczych wskaźników oceny obiektów inwentarskich dla bydła mlecznego. We wszystkich badanych obiektach z uwięziowym systemem utrzymania stwierdzono występowanie rozwiązań niestandardowych w budynku inwentarskim, co potwierdza inwencję producentów mleka we wprowadzaniu zmian w technicznym wyposażeniu budynków inwentarskich.The paper aimed at distinguishing new indices for evaluation of barns for dairy cows including their technical equipment. The detailed investigations covered barns with tied and free-stall maintenance systems including farms with different size of dairy herds. The elaborated research questionnaire to carry out the investigations included the set of basic data concerning conditions of dairy production in the barns. During direct research visits in the investigated farms some new elements were observed in the barns and as a result new comparative indices were proposed to evaluate livestock buildings for dairy cows. The all investigated barns with tied maintenance system were characterized by the use of non-standard solutions in the area for cows. Such results of the investigations confirm imagination of dairy farm owners to implement changes in the technical equipment of the managed barns

Superconductivity Study of GaN Highly Doped by Transition Metals

GaN:Cr and GaN:Fe single crystals as well as GaN:Mn micropowders highly doped by transition metals were grown to investigate low temperature superconductivity. Magnetic measurements revealed type I superconductivity with $T_{C} ≈ 6 K$ and $H_{C} ≈ 600 Oe$, identical for all compounds and also identical to that observed before in GaP:Cr and GaAs:Cr. The presence of amorphous inclusions of gallium may explain existing superconductivity as a result of a phase transition leading to β-Ga during cooling down of the sample. Since the observed parameters are close to those characteristic for superconducting Ga(II) this possibility could not be ruled out