Luminescence Emission Wavelength Research Articles

Study of thermoluminescence characteristics of quartz for high radiation doses (>1kGy): Implications for extending the luminescence dating range

Quartz is an omnipresent abundant natural mineral, used for luminescence dating. Lately, quartz optically stimulated luminescence (OSL) technique is widely used to estimate the equivalent doses (De) for dating geological events (up to 250 Gy, limited by saturation). Some works report thermoluminescence (TL) saturation around ∼ (10–40) kGy. Still dose estimates for such high radiation dose (HRD) range are not achieved. Significant research exists about luminescence response for low dose ranges (<250 Gy) but limited studies are done for HRDs (>1 kGy). This work characterizes the luminescence response of quartz for HRDs (1–21 kGy) to improve existing understanding of luminescence mechanism. Results show that the characteristics of the trap (<200 °C) differ significantly at HRDs than low doses. TL in multi-spectral detection (UV–Visible) band suggest an increase in 340–380 °C peak intensity up to 11 kGy dose. The measurements of saturation dose suggest that it depends on the trapping centres but is independent of recombination centres for the samples used for study. The traps are found bleachable by sunlight, reducing TL signal to residual levels in 1 h. Further, the bleachability is found to be anti-correlated with luminescence emission wavelength. At HRDs luminescence sensitivity is influenced by dose given in previous cycle which is difficult to correct by routine normalization procedures. The work also explores the various normalization methods to find appropriate method for HRD estimation and recommends the use of mass normalization as other normalization methods do not correct the sensitivity changes at HRDs adequately.

Organic phosphor based fiber-optic sensor for detection of UV radiation

The paper presents a simple and low-cost fiber-optic sensor for detection of UV radiation. A sensor construction consists of a silica capillary with a photoactive composition based on an organic phosphor, organic solvent and epoxyacrylate inside and a multimode optical fiber in contact with each other. By adjusting the proportion of components in a photoactive composition, it is possible to obtain a pronounced optical signal at wavelength near 440 nm which is the luminescence emission wavelength of the chosen organic phosphor. The potential of using the construction as a UV sensor is confirmed by the linear dependence of the optical signal amplitude at the fiber output on the optical power supplied to the fiber input.

Tuning violet to green emission in luminomagnetic Dy,Er co-doped ZnO nanoparticles

This paper discusses the synthesis of undoped ZnO, 2 mol% Dy doped ZnO, 2 mol% Er doped ZnO and 1 mol% Dy,Er co-doped ZnO nanoparticles by simple combustion technique and the characterization of their structural, morphological, magnetic and optical properties by X-ray diffraction (XRD), X-Ray Photoelectron Spectroscopy(XPS), Field Emission Scanning Electron Microscope (FESEM), High Resolution Transmission Electron Microscope (HRTEM), Diffuse Reflectance Spectroscope (DRS), Vibrating Sample Magnetometer (VSM) and Photoluminescence(PL). All samples are of hexagonal wurzite type structure which was found from XRD analysis. The effects of annealing on morphology and luminescence emission wavelengths were noticed in FESEM and PL, respectively. As-prepared sample displayed spherical morphology and annealed co-doped sample showed interwoven hexagonal stacking like morphology. VSM revealed the room temperature ferromagnetism in doped samples. The photoluminescence under the UV and IR excitations was observed in experiment. The as-prepared samples had violet region emission at the 325 nm excitation. The annealed samples had green region emission under the same excitation. Due to the annealing effect, the enhancement of upconversion luminescence intensity in co-doped sample in green (535 nm) and red (665 nm) regions was observed at the 980 nm excitation.

High-Efficiency InGaN/GaN Core–Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop

In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core–shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core–shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.

Study of the luminescence properties of a natural amazonite

Most gemstones, being natural materials (silicates, carbonates, phosphates, etc.), exhibit luminescence emission. This property could be potentially employed for personal dosimetry in the case of radiation accident or radiological terrorism where conventional monitoring has not been established. We, herein, report on the thermoluminescence (TL), radioluminescence (RL) and infra-red stimulated luminescence (IRSL) response of a well-characterised natural amazonite (KAlSi3O8) that, due to its bright blue-green colour when polished, is used as a gemstone. The luminescence emission wavelengths, intensities and thermal kinetics of the amazonite luminescence curves reveal that the ultraviolet band measured on amazonite aliquots is similar to other common K-rich feldspars. On this basis, one can conclude (i) association between twinning and the UV-blue TL emission can be related to structural defects located in the twin-domain boundaries where ionic alkali-self-diffusion, irreversible water losses and irreversible dehydroxylation processes can be involved. (ii) Amazonite exhibits a complex structure with several planar defects (twinning and exsolution interphases which can hold hydroxyl groups, water molecules, etc.) and point defects (impurities, Na, Pb, Mn, etc.) that can act as luminescence centres, and in fact, green and red emissions are respectively associated with the presence of Mn and Fe impurities. Finally, (iv) the thermal stability tests performed on the TL emission of the amazonite confirm a continuum in the trap distribution, i.e. progressive changes in the glow curve shape, intensity and temperature position of the maximum peak.

Luminescence properties of “double-stranded staircase” copper(i) halide coordination polymers with N-containing ligands

A set of CuIXL coordination polymers (X = Cl, Br, I; L = derivatives of pyrazine and bipyridine) with double-stranded staircase structures was analyzed by X-ray crystallography and luminescence spectroscopy to find a relationship between the structure and luminescence properties of the polymers. Our measurements have proved that luminescence emission wavelengths varied between 500–750 nm, after the polymers were irradiated by light with a wavelength of 370 nm. Although each coordination polymer has shown different emission maximum, we observed several interesting trends related to the structure of the compounds. There is a clear correlation between the emission maxima and the halide size and/or Cu–X distance, respectively. On the other hand, the substitution of the ligand L (pyrazine derivatives, 4,4′-bipyridine) has no significant contribution to the emission spectra. This observation supports the theory that the halide to metal charge transfer (XMCT) plays a key role in the photoluminescence of staircase polymers.

Correlating composition and luminescence in AlInGaN epilayers

Epilayers of the quaternary alloy Al x In y Ga 1− x− y N have been grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy. The emission properties and elemental compositions of these samples were evaluated simultaneously and intercorrelated by combining hyperspectral cathodoluminescence imaging and wavelength-dispersive X-ray mapping. Use was made of inherent variations in growth temperature across a single epilayer to study the resultant effect on the different metal fractions and luminescence emission wavelength. By examining statistical correlations in this data, the interdependence of the fractions of constituent binary compounds, together with the associated changes in emission characteristics, can be clarified without the need to grow a systematic series of samples.

Influence of MOVPE growth temperature on the structural and optical properties of InGaN MQW laser diodes

The morphological and optical properties of InGaN multiple quantum wells (MQWs) emitting at 405 nm are studied with respect to the MQW growth temperature. The latter was varied between 760 and 840 °C in structures grown on c-plane sapphire substrates by metal-organic vapor-phase epitaxy (MOVPE). The indium content in the quantum well was kept constant for all temperatures by adjusting the trimethylindium supply. The MQWs were inserted as active region in both optically pumped laser heterostructures and laser diodes (LDs). We found that low growth temperatures result in a reduced spatial uniformity of the luminescence emission wavelength due to well thickness variations, whereas at higher temperatures it is difficult to obtain a spatially homogeneous indium concentration. A minimum threshold power density for optically pumped lasing was found for growth temperatures of the active region between 780 and 820 °C. LDs with an MQW grown at these conditions showed an onset of lasing at a current density of 6.5 kA/cm 2 with output powers of more than 350 mW.

Paleohydrological Records from Peat Profiles and Speleothems in Sutherland, Northwest Scotland

Paleohydrological changes during the late Holocene are inferred from humification, testate amoebae, and pollen evidence from three blanket peat profiles in northwest Scotland. Replicate peat humification records from the Traligill basin share the same patterns of change for a 600-yr period of overlap between 1800 and 2400 cal yr B.P. The shared patterns, inferred from samples with a resolution of 5–13 yr, represent basinwide hydrological changes. In a nearby, but hydrologically separate, area with caves beneath peat, the luminescence emission wavelength measured in two speleothem samples correlated with the humification record in the overlying peat. This correlation implies that speleothem luminescence emission wavelength depends primarily on decay rates in the soils from which drip waters are derived, as long as there is no major change in soil or vegetation. The peat and speleothem records from the cave site further correlate with the peat records from the Traligill basin. Taken together, the records thus represent a regional climatic signal. Peaks in surface wetness replicated in two or more records occur at ca. 2300, 2090, 2030, 1820, 1600, and 1440 cal yr B.P. Further peaks occur at 800, 570, and 115 cal yr B.P. in the humification and stalagmite records that extend to the present day. Correlative changes have been observed, not only in other peat records from Scotland but also in ice accumulation at GISP2. These further correlations imply that precipitation regimes in Scotland and Greenland were in phase during the late Holocene.

A comparative study of optical properties of NaOH peat extracts: implications for humi®cation studies

Assessment of the degree of decay of peat (humification) in ombrotrophic mires has become a standard technique for palaeoclimatic reconstruction, based on the finding that decay is primarily determined by surface wetness and temperature at the time of peat deposition. Determination of humification is undertaken by colorimetric measurement of an alkali extract of the peat at 540 nm. Humification is proportional to the amount of humic matter dissolved by this extraction process, although few researchers convert results to a quantitative measure of humification expressing results as percentage light transmission through the peat. This paper uses luminescence spectroscopy to assess the chemical composition of these extracts. Luminescence excitation and emission wavelengths suggest that high molecular weight acids (‘humic acids’) are altered by the extraction procedure to form lower molecular weight acids (‘fulvic acids’), amino acids and polysaccharides. Percentage transmission is principally related to luminescence emission wavelength and thus to molecular weight of the compounds present. Luminescence emission shows much more sensitivity to peat composition and demonstrates that different plant species may be affected to different degrees by the NaOH extraction process. The findings broadly support the underlying principle of colorimetric determination of ‘humification’ whereby transmission levels decrease with increasing plant breakdown, but show that it is based on an inadequate understanding of the chemical processes occurring in peat decay and preparation procedures. Luminescence spectroscopy provides a technique for resolving these issues.

High-resolution records of soil humification and paleoclimate change from variations in speleothem luminescence excitation and emission wavelengths

Recent advances in the precision and accuracy of the optical techniques required to measure luminescence permit the nondestructive analysis of solid geologic samples such as speleothems (secondary carbonate deposits in caves). In this paper we show that measurement of speleothem luminescence demonstrates a strong relationship between the excitation and emission wavelengths and both the extent of soil humification and mean annual rainfall. Raw peat with blanket bog vegetation has the highest humification and highest luminescence excitation and emission matrix wavelengths, because of the higher proportion of high-molecular-weight organic acids in these soils. Brown ranker and rendzina soils with dry grassland and woodland cover have the lowest wavelengths. Detailed analysis of one site where an annually laminated stalagmite has been deposited over the past 70 yr during a period with instrumental climate records and no vegetation change suggests that more subtle variations in luminescence emission wavelength correlate best with mean annual rainfall, although there is a lag of ∼10 yr. These results are used to interpret soil humification and climate change from a 130 ka speleothem at an upland site in Yorkshire, England. These data provide a new continuous terrestrial record of climate and environmental change for northwestern Europe and suggest the presence of significant variations in wetness and vegetation within interglacial and interstadial periods.

InGaAs/InP strained layer quantum wells grown by molecular beam epitaxy

Different heterostructures containing InGaAs/InP quantum wells, separate confinement heterostructures and superlattices are grown by molecular beam epitaxy on InP substrates. These layers are grown in tensile and compressive strain and their luminescence emission wavelength is kept around 1550 nm. The growth parameters (temperature, substrate quality) are found to be of prime importance to obtain high quality materials.