We present here a photonic chip based axicon like lens that has a 850 um long central lobe, with a diameter of 5.7 um. The 1.52 mm x 1.38 mm device consists of circular grating with a novel azimuthal apodization to increase light penetration depth by an order of magnitude and multiple stages of 1x2 multimode interferometer splitters/combiners. We characterize the axicon with a swept source laser (1300 +/- 50 nm) coupled in with a GRIN lens onto the device, with the light out-coupled from a regular grating coupler. We also characterize the spectral performance of the device, using balanced homodyne detection to resolve the power, and show that the position of the central lobe does not vary significantly with wavelength.
Asymmetric contacts or split gate geometries can be used to obtain rectification, electroluminescence (EL) and photocurrent from carbon nanotube field effect transistors. Here, we report devices with both split gates and asymmetric contacts and show that device parameters can be optimised with an appropriate split gate bias, giving the ability to select the rectification direction, modify the reverse bias saturation current and the ideality factor. When operated as a photodiode, the short circuit current and open circuit voltage can be modified by the split gate bias, and the estimated power conversion efficiency was 1×10-6. When using split gates and symmetric contacts, strong EL peaking at 0.86 eV was observed with a full width at half maximum varying between 64 and 120 meV, depending on the bias configuration. The power and quantum efficiency of the EL was estimated to be around 1×10-6 and 1×10-5 respectively.
Photoluminescence (PL) and excitation spectra of Bi melt-doped oxide and chalcogenide glasses are very similar, indicating the same Bi center is present. When implanted with Bi, chalcogenide, phosphate and silica glasses, and BaF2 crystals, all display characteristically different PL spectra to when Bi is incorporated by melt-doping. This indicates that ion implantation is able to generate Bi centers which are not present in samples whose dopants are introduced during melting. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi2+ and Bi clusters.
Yanina Fedorenko, Mark Hughes, Julien Colaux, C. Jeynes, Russell Gwilliam, Kevin Homewood, Jin Yao, Dan Hewak, Tae-Hoon Lee, Stephen Elliott, B. Gholipour, Richard Curry
Doping of amorphous chalcogenide films of rather dissimilar bonding type and resistivity, namely, Ga-La-S, GeTe, and Ge-Sb-Te by means of ion implantation of bismuth is considered. To characterize defects induced by ionbeam implantation space-charge-limited conduction and capacitance-voltage characteristics of amorphous chalcogenide/silicon heterojunctions are investigated. It is shown that ion implantation introduces substantial defect densities in the films and their interfaces with silicon. This comes along with a gradual decrease in the resistivity and the thermopower coefficient. It is shown that conductivity in GeTe and Ge-Sb-Te films is consistent with the two-type carrier conduction model. It is anticipated that ion implantation renders electrons to become less localized than holes leading to electron conductivity in certain cases as, for example, in GeTe.
In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide
(GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping
concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/&tgr;)&bgr;], where &tgr; is
the fluorescence lifetime and &bgr; is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped
GLS was 30 &mgr;s and 67 &mgr;s respectively. We validate the use of the stretched exponential model and discuss the possible
microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1%
(molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/&tgr;1)+ b*exp-(t/&tgr;2),
where &tgr;1 and &tgr;2 are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and
slow components are 5 &mgr;s and 30 &mgr;s respectively and for titanium they are 15 &mgr;s and 67 &mgr;s respectively. We also show
that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host gallium lanthanum
oxy-sulphide (GLSO) is 43 &mgr;s and 97 &mgr;s respectively, which is longer than that in GLS. From this we deduce that
vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical
concentration they become saturated and low efficiency sulphide sites start to be filled.
We show that in the presence of fullerene complexes the optical properties of PbS QDs are significantly modified. The
absorption of the PbS QDs is observed to shift to a higher energy when fullerene complexes are introduced. Upon direct
excitation of the PbS below the fullerene absorption a corresponding blue shift in PL spectra of the PbS QDs is observed.
The strength of this blue-shift can be related to the fullerene concentration in most cases and is accompanied by a
broadening of the emission spectrum. When exciting the samples at high energy 3.4 eV (363 nm) the strength of these
effects is increased with a maximum blue-shift in the PL spectrum of 261 meV and 167 meV occurring for the C60 and
PCBM doped samples respectively. The origin of the observed behavior cannot be confirmed at this time and is the focus
of ongoing studies. However, we briefly discuss the results obtained in relation to the strong electron accepting nature of
the fullerene complexes used.
We presented detailed spectroscopic data obtained from Nd3+ pyridine-2,6-dicarboxylic acid based complexes in which the 4-position of the pyridine ring has been substituted with OH and Cl. In each case the ligands formed stable complexes with the Nd3+ ion without the requirement for any additional 'neutral' ligand to satisfy the 8-9 coordination requirement of the lanthanide ion. Photoluminescence is observed from both the ligand (centered ~700 nm) and the Nd3+ ion (at ~900 nm, 1064 nm, and 1320 nm due to the 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F13/2 → 4I9/2 transitions respectively) following excitation in the low energy tail of the ligand π → π* absorption. The intensity of the ligand emission and sensitized Nd3+ emission was found to be dependent on the substituted 4-position of the pyridine ring. The origin of the observed phenomena are discussed in relation to the energy transfer process from ligand to Nd3+ ion and the nonradiative relaxation of the sensitized Nd3+ ion. These results suggest that further modification of the ligand through complete halogenation and/or addition of other functional groups may provide an attractive route to obtaining an efficient near-infrared emitting organolanthanide complex.
In this paper we report the spectroscopic data for samples of 0.031% iron, 0.017% nickel, 0.01% chromium and 0.017% cobalt (molar) doped gallium lanthanum sulphide (GLS) glass. Photoluminescence (PL) with a full width half maximum (FWHM) of around 500 nm and peaking between 1120 nm and 1460 nm is observed when excited using wavelengths of 850 nm and 1064 nm. The emission lifetime for nickel-doped GLS at 300 K was measured to be 40 μs. Photoluminescence excitation (PLE) peaks for chromium-doped GLS at 700 nm and 1020 nm have been observed. By comparisons of our spectroscopic data to that of transition metals doped into other hosts we determine the oxidation states of the transition metal ions and propose transitions for the observed spectroscopic peaks.
The infrared (IR) spectrum is of significant importance in many defence applications including free-space communication, thermal imaging and chemical sensing. The materials used in these applications must exhibit a number of suitable properties including mid-IR transparency, rare-earth solubility and low optical loss. When moving towards miniaturised optical devices one tends to adopt the concepts introduced by integrated optics; multiple devices operating harmoniously on a single photonic chip. Our work focuses on the use of a laser to directly write into a novel chalcogenide glass to engineer optical waveguide devices. Our material of choice is gallium lanthanum sulphide (Ga:La:S) glass, an exceptional vitreous chalcogenide material possessing these aforementioned properties as well as a broad range of other properties. These Ga:La:S glasses have a wide transmission window between 0.5 to 10 μm. Furthermore, these low-phonon energy glasses have a high transition temperature (Tg = 560°C), high refractive index, the highest reported non-linearity in a glass, excellent rare-earth solubility with well documented near-mid IR spectroscopic properties. We report on low loss single-mode active channel waveguides in Ga:La:S glass engineered through direct laser writing (λ= 244 nm). We discuss laser operation at 1.075 µm (neodymium) and IR emission at 1.55, 2.02 and 2.74 µm (erbium) from these waveguides.
Electroluminescent diodes fabricated on silicon substrates which emit at a wavelength of 1.5 micrometer have been demonstrated. The diodes operate at room temperature and exhibit good I-V characteristics. The diodes use an erbium tris(8-hydroxyquinoline) (ErQ) layer as electron transporting and emitting layer and use N, N'-diphenyl-N, N'-bis(3-methyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the hole transporting layer. Hole injection into the diodes is from a p++ silicon substrate anode and aluminum is used as the cathode electrode. The devices demonstrated start to exhibit electroluminescence at a voltage of approximately 17 V and the electroluminescence intensity rises sub-linearly with the current density through the device. At a drive voltage of 33 V the diodes have an internal efficiency of approximately 0.01%. We have measured the luminescence lifetime for the 1.5 micrometer emission and obtained a value of approximately 200 microsecond(s) . Using this value and estimating the total concentration of erbium present in the diodes we calculate a theoretical maximum optical power generation in these diodes of approximately 100 mW.
We have demonstrated that it is possible to product organic light emitting diodes containing lanthanide ions which provide sharp electroluminescence emission at a range of wavelengths in the near infrared including 0.9 micrometers , 0.98 micrometers , 1.064 micrometers , 1.3 micrometers and 1.5 micrometers . For devices grown on ITO substrates we have demonstrated bright electroluminescence at drive voltages of approximately 12 V. We have shown that these diodes can be integrated onto silicon substrates and use the silicon as the anode of the device. For erbium based devices which emit at a wavelength of 1.5 micrometers we have demonstrated devices with room temperature internal efficiencies of approximately 0.01% at a drive voltage of 33 V.
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