The initial rate of loss of luminescence due to infrared stimulation of K-feldspars

Repeated stimulation by infrared of a feldspar sample causes a reduction in the luminescence signal. The initial rate of loss of luminescence due to infrared stimulation is investigated for a microcline and an orthoclase with preheating at 150°C, 180°C and 220°C for times ranging from 20 to 2400 s.     

Effects of bleaching on the sensitivity to dose of the infrared-stimulated luminescence of potassium-rich feldspars from Ynyslas, Wales

Reduction of the luminescence signal to a residual level before irradiation is an inherent part of the regeneration method of equivalent dose (ED) determination, but is likely to lead to changes in the sensitivity of the dosimeter. Sensitivity changes caused by different methods of reduction of the infrared- stimulated luminescence (IRSL) signal have been investigated by subjecting potassium-rich feldspars extracted from modern dune sand from Ynyslas, on the Dyfi Estuary in Wales, to repeated cycles of removal of the luminescence signal and beta irradiation. The methods used to remove the signal were exposure to natural sunlight, a solar simulator and infrared-emitting diodes with a wavelength of 880Δ 80 nm and heating to 450°C.     

The relationship between thermal activation energy,infrared stimulated luminescence and anomalous fading of K-feldspars

A strong dependence of thermal activation energy (TAE) on infrared (IR) stimulation time for the infrared stimulated luminescence (IRSL) signal was observed for K-feldspar grains extracted from several sediments and granites from China. A TAE value as low as ～0.1 eV was observed at the beginning of IR stimulation and increased to ～0.45 eV after 90 s. For a trap depth of ～2 eV below the conduction band for the IRSL traps, the TAE value of ～0.45 eV is consistent with the energy gap between the excited states (～0.5 eV below the conduction band) and conduction band. This phenomenon is explained as the result of the coexistence of thermally assisted recombination via conduction band or band-tail states hopping and athermal tunnelling recombination of electrons from the excited states under IR stimulation, leading to the observation of a higher anomalous fading rate in the initial part of the IRSL decay curve.     

Natural variations in the properties of TL and IRSL emissions from metamorphic and volcanic K-feldspars from East Africa: Assessing their reliability for dating

The elevated temperature infrared stimulated luminescence (IRSL) and post-IR IRSL signals of potassium (K)-feldspars have recently garnered attention for their minimal rates of anomalous fading. The post-IR IRSL signal has been used to obtain age estimates for geological deposits, mostly in Europe. Studies on the behaviour of the IRSL and post-IR IRSL signals of K-feldspars from a wider range of geographic regions and depositional contexts are needed, particularly for regions where the OSL signal from quartz is poorly behaved. Discrepancies in the literature regarding the behaviours of the IRSL and TL signals of K-feldspars also highlight the need to characterise the behaviours of samples from a wide variety of contexts. This paper begins to address this problem by characterising and comparing the IRSL signals of a metamorphic and a volcanic K-feldspar sample from two sites in East Africa, a region in which the OSL signal from quartz has generally proven problematic for dating. We demonstrate that the metamorphic and volcanic K-feldspars have substantially different TL glow curves that respond differently to IR stimulation. The sample of metamorphic K-feldspar from Tanzania (MR9) has a peak at 430 °C that is associated with the IRSL signal and an optically less-sensitive peak at 350 °C, while the sample of volcanic K-feldspar from Ethiopia (MB3) exhibits a single broad TL region centred at ～230 °C that responds differently to IR stimulation. Differences in the change of IRSL decay curve shape with stimulation temperature suggest that the processes of IRSL production many vary between the two samples. Using dose recovery tests, we demonstrate that the IRSL (50 °C), IRSL (225 °C) and post-IR IRSL (50 °C, 225 °C) signals of sample MR9 are suitable for dose and age estimation using the single-aliquot regenerative-dose procedure, while those of sample MB3 are less suitable. The post-IR IRSL signal of the latter sample performs poorly in tests of SAR suitability and the three signals exhibit extremely high fading rates over laboratory timescales (g_2days > 19%/decade).     

Efficient luminescence from porous silicon

Photoluminescence measurements are carried out on porous silicon layers. We show the enhancement and stabilization of the luminescence when depositing a silicon nitride layer on top of porous layers.We also demonstrate that direct- and remote-plasma nitridation are good ways to reduce the ageing effect of porous silicon layers due to a passivation of dangling bonds.     

Optically stimulated luminescence from BeO ceramics: An LM-OSL study

Optically Stimulated Luminescence (OSL) signals of BeO ceramics were investigated using continuous wave (CW) OSL and Linearly Modulated (LM) OSL. It was found that both curves can be approximated using a linear combination of two first-order components. Experiments on the measurement temperature dependence have shown that these two components have nearly the same thermal quenching energies around 0.57 eV. Dependences of the OSL signal on preheat temperature and radiation dose were also examined. Thermal annealing experiments have shown that OSL signals originate from traps which are unstable near 340 °C, thus proving the suitability of the signals for dosimetric purposes. Dose response was found to be linear and a minimum detectable dose of ～10 μGy was found.     

The luminescence at 0.795 eV from GaAs:Nb: A Zeeman spectroscopy

The 0.795 eV photoluminescence line from GaAs:Nb is studied by Zeeman spectroscopy. It is compared with that of other transition ions in the d² configuration. We conclude that it corresponds to a ¹A₁ → ³A₂ transition at a Nb³⁺ (4d²) substitutional ion.     

Thermally stimulated luminescence from alkaline earth borates

The thermally stimulated luminescence from XB₂O₄ (X=Ca,Sr,Ba) has been investigated. The results on CaB₂O₄ and SrB₂O₄ are being reported here for the first time. In both cases, the emission is found to be quite intense, contrary to the case with BaB₂O₄. The presence of two peaks in the glow curves is noted over the temperature range of 300-570 K. The emission spectra corresponding to both the peaks have been observed to be identical, consisting of two broad emissions, one in the UV and other in the blue-green regions. The emission is apparently quite different from that of BaB₂O₄ in which case only very weak emission spreading over a broad wavelength range around 410 nm is observed. This result has been understood in terms of the overlap between the excitation and the emission spectra.     

Indirect gap luminescence from tellurium-doped gallium antimonide

Photoluminescence spectra of tellurium-doped GaSb samples are reported for 1.06 μm laser Q-switched excitation. Room temperature data are reported for excitation levels up to 1 MW cm^?2. Besides the direct gap emission the data show an additional peak at an energy corresponding to the L-Γ indirect gap. It is suggested that this additional peak is associated with tellurium impurity levels located near the L conduction band minima.     

Polariton effects in luminescence from ZnTe crystals: surface and bulk polaritons

The exciton-polariton luminescence spectra of the ZnTe cystals are investigated in the region of the ground (n= 1) exciton state. In addition to emission of the both branches of bulk polaritons, luminescence of surface polaritons is first revealed. The temperature dependence of luminescence of the bulk and surface polaritons is considered.     

Photostimulated luminescence flash: from scientific photography to photonics of nanostructured materials

We have analyzed the possibilities of using the phenomenon of photostimulated luminescence flash for optical diagnosing of energy levels of structural and impurity defects of semiconductor crystals and nanostructures. New data on the spectra of deep localized states associated with adsorbed few-atom clusters Zn _n on the surface of ZnS; clusters Cd _n , Cu _n , and Ag _n on the surface of CdS; and clusters Ag _n on the surface of AgBr(I) have been presented, as well as results of investigation of photostimulated assembling processes of few-atom clusters on the surface of crystals using this phenomenon. We are the first to show the potential of the luminescence flash technique for studying the mutual arrangement of the levels of dye molecules and the bands of the crystal on the surface of which they are adsorbed, as well as of the spectra of localized states in colloidal CdS semiconductor quantum dots.     

Mid-infrared luminescence from coupled quantum dots and wells

Coupled nanostructures have been developed in the InAs/InSb/GaSb materials system in order to extend the emission wavelength further into the infrared, beyond 2 μm. The samples studied consist of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix, in which the coupling has been altered by changing the thickness of a GaSb spacer layer. The overall transition energy of the combined dot–well system is generally reduced with respect to the dots and well only but the dependence on spacer thickness is more complex than that expected from a simple envelope function model.     

Blue luminescence from the InGaN multiple quantum wells

We have fabricated very high-quality In_0.13Ga_0.87N/GaN multiple quantum wells with thickness as small as on (0 0 0 1) sapphire substrate using metal organic chemical vapour deposition (MOCVD). We have investigated these ultra-thin multiple quantum wells by continuous wave (cw) and time resolved spectroscopy in the picosecond time scales in a wide range of temperatures from 10 K to 290 K. In the luminescence spectrum at 10 K we observed a broad peak at 3.134 eV which was attributed to the quantum wells emission of InGaN. The full-width at half-maximum of this peak was 129 meV at 10 K and the broadening at low temperatures which was mostly inhomogeneous was thought to be due to compositional fluctuations and interfacial disorder in the alloy. The ultra narrow width of the quantum well was found to have a very profound effect in increasing the emission linewidth. We also observed an intense and narrow peak at 3.471 eV due to the GaN barrier. The temperature dependence of the luminescence was studied. The peak positions and intensities of the different peaks were obtained after a careful Lorentzian analysis. The activation energy of the InGaN quantum well emission peak was estimated as 69 meV. The lifetime of the quantum well emission was found to be 720 ps at 10 K. The results were explained by considering the localization of the excitons due to potential fluctuations. At higher temperatures the non-radiative recombination was found to be very dominant.     

Plasmon surface polariton luminescence from periodic metal gratings

When a gold grating is illuminated at an appropriate energy, polarization, and angle to excite a plasmon surface polariton (SP) all lower energy radiative SP states emit light. This enables the dispersion of SP states to be mapped by luminescence providing an alternative to reflectivity measurements. A similar effect has been observed for bare silver gratings, and silver gratings coated with several layers of cadmium arachidate by Langmuir-Blodgett technique. Two additional effects have been observed for Au gratings. First, one can obtain emission from radiative SP states by exciting the interband transition directly with photons of energy greater than approximately 2.4 eV. At these energies, SP states do not exist because the metal dielectric function has a large imaginary part. This is significant because it suggests that the degradation pathway involves electron-hole pair states as intermediates. Second, some gold gratings show $\text{surface enhanced Raman}$ of molecular species superimposed on the SP luminescence emission.     

Experimental evidence of selective heating of molecules adsorbed in nanopores under microwave radiation

We have performed in situ quasielastic neutron scattering (QENS) measurements on zeolite-guest systems under microwave irradiation, for comparison with corresponding simulations. Both experiment and simulation reveal selective heating of methanol in silicalite, but little to no heating of benzene in silicalite. Effective translational and rotational temperatures extracted from QENS data under microwave heating were found to depend on microwave power. In agreement with simulation, QENS rotational temperatures significantly exceed translational ones at high microwave power, thus providing the first microscopic proof for athermal effects in microwave-driven nanopores.     

Yellow stimulated luminescence from potassium feldspar: Observations on its suitability for dating

Yellow stimulated luminescence (Y-OSL) is the light detected from potassium-rich feldspars at 410 nm under stimulation by a yellow light source emitting 590 nm. The investigation of this study aimed at understanding basic luminescence physics of Y-OSL in order to assess the suitability of the technique for dating. The Y-OSL signal properties tested were signal intensity, thermal assistance, thermal stability, sensitivity to daylight and the suitability of a single aliquot regenerative (SAR) protocol to be employed for equivalent dose (D_e) estimation. D_e measurements were conducted on samples of Holocene, last glacial and Tertiary age. The tests were undertaken on sedimentary feldspar separates extracted from aeolian, fluvial and coastal deposits.Results from experiments show that the signal intensity increases by measuring Y-OSL at elevated temperature suggesting thermal assistance characteristics similar to infrared stimulated luminescence (IRSL). The yellow stimulated signal remains unaffected by preheat temperatures up to ～200 °C suggesting higher thermal stability than the IRSL signal. The Y-OSL signal is less light sensitive than the IRSL signal and D_e residuals obtained from modern samples are up to 7 Gy indicating suitability of the technique for ‘older’ and well-bleached sediments. The dose recovery tests successfully recovered the given dose if the specific light sensitivity of Y-OSL is taken into account. For every sample Y-OSL D_e values obtained by a single aliquot regenerative dose protocol (SAR) are higher than those obtained by an IRSL SAR approach. From these results we infer high thermal stability and a minimal anomalous fading of the Y-OSL signal. We conclude that Y-OSL has a high potential to date Quaternary sediments that were sufficiently bleached in nature.