Total Light Output Research Articles

Real-World Urban Light Emission Functions and Quantitative Comparison with Spacecraft Measurements

We provide quantitative results from GIS-based modelling of urban emission functions for a range of representative low- and mid-rise locations, ranging from individual streets to residential communities within cities, as well as entire towns and city regions. Our general aim is to determine whether lantern photometry or built environment has the dominant effect on light pollution and whether it is possible to derive a common emission function applicable to regions of similar type. We demonstrate the scalability of our work by providing results for the largest urban area modelled to date, comprising the central 117 km2 area of Dublin City and containing nearly 42,000 public lights. Our results show a general similarity in the shape of the azimuthally averaged emission function for all areas examined, with differences in the angular distribution of total light output depending primarily on the nature of the lighting and, to a smaller extent, on the obscuring environment, including seasonal foliage effects. Our results are also consistent with the emission function derived from the inversion of worldwide skyglow data, supporting our general results by an independent method. Additionally, a comparison with global satellite observations shows that our results are consistent with the deduced angular emission function for other low-rise areas worldwide. Finally, we validate our approach by demonstrating very good agreement between our results and calibrated imagery taken from the International Space Station of a range of residential locations. To our knowledge, this is the first such detailed quantitative verification of light loss calculations and supports the underlying assumptions of the emission function model. Based on our findings, we conclude that it should be possible to apply our approach more generally to produce estimates of the energy and environmental impact of urban areas, which can be applied in a statistical sense. However, more accurate values will depend on the details of the particular locations and require treatment of atmospheric scattering, as well as differences in the spectral nature of the sources.

Influence of irradiation with fast electron beam on energy transport in praseodymium-ion doped phosphates

This paper reports the spectroscopic properties of praseodymium-doped phosphates, KLuP2O7, Sr9Sc(PO4)7, K3Lu(PO4)2 doped with Pr3+ ions. Spectra of photoluminescence (PL) upon selective UV photon excitation, PL excitation spectra as well as luminescence spectra and decay kinetics upon pulse synchrotron X-ray excitation were studied. Recordings of luminescence spectra were done with pure samples and after irradiating with fast electrons (E = 10 MeV) using linear electron accelerator. The absorbed dose varied in the range of 150–300 kGy. Pure samples demonstrated three typical channels of emission: interconfigurational d – f transitions, intraconfigurational f – f transitions and defect-related luminescence. After irradiating, two scenarios of changing optical properties were investigated: increasing of defect-related luminescence impact in total light output and “suppressing” of defect-located energy emission.

Comparative Investigation of the Chemiluminescent Properties of a Dibrominated Coelenterazine Analog.

Chemi- and bioluminescence are remarkable light-emitting phenomena, in which thermal energy is converted into excitation energy due to a (bio)chemical reaction. Among a wide variety of chemi-/bioluminescent systems, one of the most well-known and studied systems is that of marine imidazopyrazinones, such as Coelenterazine and Cypridina luciferin. Due to the increasing usefulness of their chemi-/bioluminescent reactions in terms of imaging and sensing applications, among others, significant effort has been made over the years by researchers to develop new derivatives with enhanced properties. Herein, we report the synthesis and chemiluminescent characterization of a novel dibrominated Coelenterazine analog. This novel compound consistently showed superior luminescence, in terms of total light output and emission lifetime, to natural imidazopyrazinones and commercially available analogs in aprotic media, while being capable of yellow light emission. Finally, this new compound showed enhanced chemiluminescence in an aqueous solution when triggered by superoxide anion, showing potential to be used as a basis for optimized probes for reactive oxygen species. In conclusion, bromination of the imidazopyrazinone scaffold appears to be a suitable strategy for obtaining Coelenterazines with enhanced properties.

DUV-LED packaging using high density TSV in silicon cavity and laser-glass-frit-bonded UV transmitting glass cap

This paper reports an improved deep ultraviolet LED (DUV-LED) packaging based on Si Micro-Electro-Mechanical Systems (MEMS) process technology. The Si package (Si-PKG) consists of a cavity formed by Si crystalline anisotropic wet etching and through-silicon vias (TSVs) filled with electroplated Cu. The Si-PKG is hermetically sealed by laser local heating of screen-printed glass frit. This technology allows for the use of a DUV-transparent glass substrate, which has an unmatched coefficient of thermal expansion (CTE). Using a high-density array of TSV capped with AuSn solder bumps, the cooling performance of the DUV-LED has been greatly improved. And the contribution by the Si (111) side reflection of Si-PKG to the total light output was confirmed 13 %. As a result, an optical output of 114 % (50 mW) and a volumetric light power density of 380 % (14 mW/mm3) were recorded compared with the conventional AlN-packaged device. The developed compact low-cost Si-PKG is promising for wider applications of the DUV-LED including the disinfection of the new coronaviruses.

A 10 × 10 deep ultraviolet light-emitting micro-LED array

In this work, we design and fabricate a deep ultraviolet (DUV) light-emitting array consisting of 10 × 10 micro-LEDs (μ-LEDs) with each device having 20 μm in diameter. Strikingly, the array demonstrates a significant enhancement of total light output power by nearly 52% at the injection current of 100 mA, in comparison to a conventional large LED chip whose emitting area is the same as the array. A much higher (~22%) peak external quantum efficiency, as well as a smaller efficiency droop for μ-LED array, was also achieved. The numerical calculation reveals that the performance boost can be attributed to the higher light extraction efficiency at the edge of each μ-LED. Additionally, the far-field pattern measurement shows that the μ-LED array possesses a better forward directionality of emission. These findings shed light on the enhancement of the DUV LEDs performance and provide new insights in controlling the light behavior of the μ-LEDs.

Etendue maintained white solid-state light generation by light emitting diodes pumped green aluminate green-yellow phosphor

We propose a technique to generate etendue maintained white light. The proposed technique uses three high-power blue light emitting diodes (LEDs) with identical characteristics to pump green aluminate (GAL) green-yellow phosphor coated on the inner channel of a waveguide. The technique offers two methods of generation of white light. Standalone partial conversion of blue to green and yellow light by GAL phosphor, combined with unconverted blue light, produces white light homogenized within the light guide. Complete conversion of blue to green and yellow light with the further addition of blue and red wavelengths from additional LED sources multiplexed with the output is also possible to further increase total white light output. Following design and optical modeling to prove the concept, the proposed technique is demonstrated, which shows white light emissions from the waveguide with no increase in aperture size while the original LED etendue is maintained. The proposed technique offers an alternative to low-lifetime, low-efficiency xenon lamps for light sources in etendue critical applications such as endoscopy.

PHOTOTOXICITY OF α-TERTHIENYL AND PSORALENE INROSE AND MUSTARD APHIDS (MACROSIPHUM ROSAE & LIPAPHIS ERYSIMI) IN DOON VALLEY

Climate change has an impact on agriculture and insect pests that affect the crop production. Aphid pests occur throughout the temperate region of the world andcause direct damage by sucking plants sap which affects growth and yield of the crops. Species of aphids are diverse and ubiquitous but their importance among crop differs.Ultraviolet radiation (UVR) is an electromagnetic radiation and constitutes about 10% of the total light output of sunlight. Ultraviolet-B coming due to ozone depletion is the most photo chemically reactive wavelength of solar radiation and important stressor to organisms particularly in their early stages of life and affect ecosystem. Psoralene and alpha- terthienyl are naturally occurring plant metabolites found in many crops and become photo reactive in presence of solar ultraviolet- B radiation. Measurement of solar ultraviolet radiation (UV-B and UV-E) was performed in Garhwalregion of Uttarakhand. Morphological, behavioural changes, mortality rate and glutathione contents were observed in mustard and roseaphids after ultraviolet-B irradiation with psoralene and α-terthienyl photo sensitizers. UV-B and UV-E radiation showed seasonal, diurnal and altitudinal variations. α- terthienyland psoralenewith ultraviolet-B radiation showed stunted growth, morphological changes, low reproduction and high mortality up to 26% in aphids. Reduction in glutathione (GSH) level in aphids was also observed after UV- B and photosensitizersexposure.Enhanced UV-B was found more toxic with photosensitizers andthus, can be used as natural insecticide. Dose, intensity and species dependent changes in toxicity of psoralene and α- terthienyl were observed in aphids. Resultsindicate that UV-B radiation with photosensitizers has toxic effect on aphids population, dispersal and diversity. Psoralene was found more toxic than α- terthienyl in aphids. Mustard aphid (Lipaphis erysimi) was found more sensitive than rose aphid (Macrosiphum rosae).

Fast Neutron Imaging with Semiconductor Nanocrystal Scintillators.

Fast neutrons offer high penetration capabilities for both light and dense materials due to their comparatively low interaction cross sections, making them ideal for the imaging of large-scale objects such as large fossils or as-built plane turbines, for which X-rays or thermal neutrons do not provide sufficient penetration. However, inefficient fast neutron detection limits widespread application of this technique. Traditional phosphors such as ZnS:Cu embedded in plastics are utilized as scintillators in recoil proton detectors for fast neutron imaging. However, these scintillation plates exhibit significant light scattering due to the plastic-phosphor interface along with long-lived afterglow (on the order of minutes), and therefore alternative solutions are needed to increase the availability of this technique. Here, we utilize colloidal nanocrystals (NCs) in hydrogen-dense solvents for fast neutron imaging through the detection of recoil protons generated by neutron scattering, demonstrating the efficacy of nanomaterials as scintillators in this detection scheme. The light yield, spatial resolution, and neutron-vs-gamma sensitivity of several chalcogenide (CdSe and CuInS2)-based and perovskite halide-based NCs are determined, with only a short-lived afterglow (below the order of seconds) observed for all of these NCs. FAPbBr3 NCs exhibit the brightest total light output at 19.3% of the commercial ZnS:Cu(PP) standard, while CsPbBrCl2:Mn NCs offer the best spatial resolution at ∼2.6 mm. Colloidal NCs showed significantly lower gamma sensitivity than ZnS:Cu; for example, 79% of the FAPbBr3 light yield results from neutron-induced radioluminescence and hence the neutron-specific light yield of FAPbBr3 is 30.4% of that of ZnS:Cu(PP). Concentration and thickness-dependent measurements highlight the importance of increasing concentrations and reducing self-absorption, yielding design principles to optimize and foster an era of NC-based scintillators for fast neutron imaging.

Bioluminescence Profiling of NanoKAZ/NanoLuc Luciferase Using a Chemical Library of Coelenterazine Analogues.

We describe here an extensive structure-bioluminescence relationship study of a chemical library of analogues of coelenterazine, using nanoKAZ/NanoLuc, a mutated luciferase originated from the catalytic subunit of the deep-sea shrimp Oplophorus gracilirostris. Out of the 135 O-acetylated precursors that were prepared by using our recently reported synthesis and following their hydrolysis to give solutions of the corresponding luciferins, notable bioluminescence improvements were achieved in comparison with furimazine, which is currently amongst the best substrates of nanoKAZ/NanoLuc. For instance, the rather more lipophilic analogue 8-(2,3-difluorobenzyl)-2-((5-methylfuran-2-yl)methyl)-6-phenylimidazo[1,2-a]pyrazin-3(7H)-one provided a 1.5-fold improvement of the total light output over a 2 h period, a close to threefold increase of the initial signal intensity and a signal-to-background ratio five times greater than furimazine. The kinetic parameters for the enzymatic reaction were obtained for a selection of luciferin analogues and provided unexpected insights into the luciferase activity. Most prominently, along with a general substrate-dependent and irreversible inactivation of this enzyme, in the case of the optimized luciferin mentioned above, the consumption of 2664 molecules was found to be required for the detection of a single Relative Light Unit (RLU; a luminometer-dependent fraction of a photon).

Using SiO2-Based Distributed Bragg Reflector to Improve the Performance of AlGaInP-Based Red Micro-Light Emitting Diode

We have investigated how different types of the reflectors affected the optical and electrical performance of AlGaInP-based micro-LEDs. Simulations showed that the AlGaAs-based epitaxial distributed Bragg reflector (DBR) had a stopband at the 610–624 nm region with reflectivity of 90%, the SiO2/TiO2 dielectric DBR gave a stopband at the 580–770 nm range with a maximum reflectivity of 99%, and the ITO/Ag metal reflector exhibited reflectivity of 90% across the 400–800 nm region. All micro-LEDs gave forward voltages of 1.895–1.960 V at 20 μA. The micro-LEDs with the dielectric DBR and metal reflector yielded 31% and 13% higher light output at 20 μA than that with the epitaxial DBR, respectively. All of the micro-LEDs contained a shoulder peak at approximately 615 nm in their electroluminescence spectra. Ray-tracing simulations exhibited that the micro-LEDs with the dielectric DBR and metal reflector produced 26% and 22% higher total light output power than the one with the epitaxial DBR, respectively. It was also shown that for the micro-LEDs with the metal reflector, some of the micro-LEDs were detached from the metal reflectors due to the interfacial voids induced as a result of agglomeration of Ag layer during fabrication process.

Investigation of the quinine sulfate dihydrate spectral properties and its effects on Cherenkov dosimetry

Recent studies have proposed that adding quinine to water while performing Cherenkov volumetric dosimetry improves the skewed percent depth dose measurement. The aim of this study was to quantify the ability of quinine to convert directional Cherenkov emission to isotropic fluorescence and evaluate its contribution to the total emitted light. Aqueous solutions of quinine were prepared with distilled water at various concentrations (0.01–1.2 g l−1). The solutions were irradiated with photon beams at 6 and 23 MV. The dependence of the light produced as a function of sample concentration was studied using a spectrometer with a fixed integration time. Spectral measurements of the luminescent solution and the blank solution (distilled water only) were taken to deconvolve the Cherenkov and quinine contribution to the overall emission spectrum. Using a CCD camera, intensity profiles were obtained for the blank and the 1.00 g l−1 solutions to compare them with the dose predicted by a treatment planning system. The luminescent intensity of the samples was found to follow a logarithmic trend as a function of the quinine concentration. Based on the spectral deconvolution of the 1.00 g l−1 solution, 52.4% ± 0.7% and 52.7% ± 0.7% of the signal in the visible range results from the quinine emission at 6 and 23 MV, respectively. The remaining fraction of the spectrum is due to the Cherenkov light that has not been converted. The fraction of the Cherenkov emission produced between 250 nm and 380 nm in the water and that was absorbed by the fluorophore reached 24.8% and 9.4% respectively at 6 and 23 MV. X-ray stimulated fluorescence of the quinine was then proven to be the principal cause to the increased total light output compared to the water-only signal. This new information reinforces the direct correlation of the solution intensity to the dose deposition.

Mapping Fishing Activities and Suitable Fishing Grounds Using Nighttime Satellite Images and Maximum Entropy Modelling

Fisheries surveys over broad spatial areas are crucial in defining and delineating appropriate fisheries management areas. Yet accurate mapping and tracking of fishing activities remain largely restricted to developed countries with sufficient resources to use automated identification systems and vessel monitoring systems. For many countries, the spatial extent and boundaries of fishing grounds are not completely known. We used satellite images at night to detect fishing grounds in the Philippines for fishing gears that use powerful lights to attract coastal pelagic fishes. We used nightly boat detection data, extracted by U.S. NOAA from the Visible Infrared Imaging Radiometer Suite (VIIRS), for the Philippines from 2012 to 2016, covering 1713 nights, to examine spatio-temporal patterns of fishing activities in the country. Using density-based clustering, we identified 134 core fishing areas (CFAs) ranging in size from 6 to 23,215 km2 within the Philippines’ contiguous maritime zone. The CFAs had different seasonal patterns and range of intensities in total light output, possibly reflecting differences in multi-gear and multi-species signatures of fishing activities in each fishing ground. Using maximum entropy modeling, we identified bathymetry and chlorophyll as the main environmental predictors of spatial occurrence of these CFAs when analyzed together, highlighting the multi-gear nature of the CFAs. Applications of the model to specific CFAs identified different environmental drivers of fishing distribution, coinciding with known oceanographic associations for a CFA’s dominant target species. This case study highlights nighttime satellite images as a useful source of spatial fishing effort information for fisheries, especially in Southeast Asia.

On the Relationship Between Scintillation Anisotropy and Crystal Structure in Pure Crystalline Organic Scintillator Materials

The scintillation anisotropy effect for proton recoil events has been investigated in five pure organic crystalline materials: anthracene, trans-stilbene, p-terphenyl, bibenzyl, and diphenylacetylene. These measurements include characterization of the scintillation response for one hemisphere of proton recoil directions in each crystal. In addition to standard measurements of the total light output and pulse shape at each angle, the prompt and delayed light anisotropies are analyzed, allowing for investigation of the singlet and triplet molecular excitation behaviors independently. This work provides new quantitative and qualitative observations that make progress toward understanding the physical mechanisms behind the scintillation anisotropy. These measurements show that the relationship between the prompt and delayed light anisotropies is correlated with crystal structure, as it changes between the pi-stacked crystal structure materials (anthracene and p-terphenyl) and the herringbone crystal structure materials (stilbene, bibenzyl, and diphenylacetylene). The observations are consistent with a model in which there are preferred directions of kinetic processes for the molecular excitations. These processes and the impact of their directional dependencies on the scintillation anisotropy are discussed.

Evaluating analytical ionization quenching correction models for 3D liquid organic scintillator detector

Proton therapy offers dosimetric advantage over conventional photon therapy due to the finite range of the proton beam, which improves dose conformity. However, one of the main challenges of proton beam therapy is verification of the complex treatment plans delivered to a patient. Thus, 3D measurements are needed to verify the complex dose distribution. A 3D organic scintillator detector is capable of such measurements. However, organic scintillators exhibit a non-linear relation to the ionization density called ionization quenching. The ionization quenching phenomenon in organic scintillators must be accounted for to obtain accurate dose measurements. We investigated the energy deposition by secondary electrons (EDSE) model to explain ionization quenching in 3D liquid organic scintillator when exposed to proton beams. The EDSE model was applied to volumetric scintillation measurement of proton pencil beam with energies of 85.6, 100.9, 144.9 and 161.9 MeV. The quenching parameter in EDSE model ρq was determined by plotting the total light output vs the initial energy of the ion. The results were compared to the Birks semi-empirical formula of scintillation light emission.

Effects of unit size on current density and illuminance of micro-LED-array

A 300 μm×300 μm light emitting diode (LED) chip is divided into nine 80 μm×80 μm units with 30 μm spacing between adjacent ones. After arraying, the total saturation light output power and the maximum injection current are enhanced by 5.19 times and nearly 7 times, respectively. In addition, the test results demonstrate that the illuminance uniformity on the receiving surface reaches the optimum when the spacing between the arrays is equal to the maximum flat condition. The larger the number of arrays, the greater the area with uniform illuminance on the receiving surface.

Pump chip and phosphor reliability of broadband light-emitting diodes

We present a study of the degradation of phosphor-based broadband (~90nm spectral peak width) colour and white LEDs. Specifically, our study looked at the reliability of the blue-emitting GaN/InGaN pump chip and the overlying phosphor in these LEDs. We have investigated thermal degradation arising from heat generation in both the pump chip and the colour-converting phosphor. The robustness of the pump chip in 1W broadband power LEDs was examined by driving them with various dc and pulsed waveforms at different temperatures. Both catastrophic and long term degradation of pump chips was investigated. Long term degradation behaviour of phosphors was studied by both ex situ and in situ heating of phosphors for hundreds of hours while their total light output was monitored. Optical energy storage in phosphors and its bearing on phosphor degradation is also discussed.

Chromium Doped Persistent Phosphors for Medical Imaging

Persistent luminescent materials or glow-in-the-dark compounds have been known for centuries, but due to their limited performance in terms of total light output, they were never used for large scale applications. It is only since about 20 years ago, when SrAl2O4:Eu,Dy was introduced as a new persistent phosphor [1], that a leap forward in both brightness and decay time was achieved. This paper has initiated substantial research, which has led to an entire family of materials, showing an appreciable afterglow for more than 24 hours [2,3]. These developments have opened up a whole new series of applications, ranging from emergency illumination, decoration and toys to medical imaging. For the latter application, materials are needed with deep red to near infrared emission, which falls in the transparency window of biological tissues. This, together with the need for red emitters for indicating emergency situations, has led to an interest in long wavelength persistent luminescence. Eu2+ is by far the most common dopant in persistent luminescent compounds. However, only very few chemically stable hosts are known, notably a number of nitrides, that allow to shift the Eu2+ emission to the deep red. Current research therefore focusses on Mn2+ and Cr3+ as valuable alternative dopants [4], as they allow to reach longer wavelengths than possible with Eu2+. Fig. 1: Principle of in vivo imaging using persistent luminescent materials. In this work, we will focus on Cr-doped ZnGa2O4 (ZGO), which is one of the most promising dopant-host combinations for near infrared emission [4]. ZGO has a normal spinel structure, where the Zn2+ and Ga3+ ions are located in octahedral and tetrahedral voids respectively. Due to their similarity with Ga3+ in charge and size, the Cr3+ ions occupy Ga-sites in the host. It has been shown that the trap states in ZGO:Cr, which are necessary to store the energy, liberated during the afterglow, are related to antisite defects: a small fraction of Ga-ions occupying Zn-sites or vice versa [5]. In addition, authors have tried to increase the number of traps by introducing different codopants and/or elements to form solid solutions with ZGO. This presentation will discuss different methods to synthesize ZGO:Cr nanoparticles which are potentially useful for in vivo medical imaging. In addition, the effects of different types of dopants on the defects and thus on the persistent luminescence will be presented. Finally, some alternative hosts for emission from Cr3+ - SrAl2O4 (ubiquitous in visible light persistent luminescence) and YAGG (yttrium aluminium gallium garnet) - are evaluated, and the toxicity of the materials, which is obviously very important for biocompatibility, is discussed. [1] T. Matsuzawa, Y. Aoki, N. Takeuchi and Y.A. Murayama, J. Electrochem. Soc. 143, 2670–2673 (1996). [2] K. Van den Eeckhout, P.F. Smet, D. Poelman, Materials 3, 2536-2566 (2010) [3] K. Van den Eeckhout, D. Poelman, P.F. Smet, Materials 6, 2789-2818 (2013) [4] Y.X. Zhuang, Y. Katayama, J. Ueda and S. Tanabe, Optical Materials 36, 1907-1912 (2014) [5] T. Maldiney, A. Bessière, J. Seguin, E. Teston, S.K. Sharma, B. Viana, A.J.J. Bos, P. Dorenbos, M. Bessodes, D. Gourier, D. Scherman, C. Richard, Nature Materials 13, 418-426 (2014) Figure 1

Persistent phosphor SrAl_2O_4:Eu,Dy in outdoor conditions: saved by the trap distribution

Persistent phosphors are a specific type of luminescent materials having the unique ability to emit light long after the excitation has ended. They are commonly used as emergency signage in near ideal, isothermal indoor situations. Recently, their energy storage capacity was relied on for outdoor situations, e.g. for glow-in-the-dark road marks and in combination with solar cells and photo catalytic processes. In this work the influence of temperature, illumination intensity and the duration of the night is critically evaluated on the performance of afterglow phosphors. The persistent luminescence of SrAl2O4:Eu,Dy green emitting phosphors is studied under realistic and idealized conditions. It is found that the light output profile is hardly influenced by the ambient temperature in a wide range. This is due to the presence of a broad trap depth distribution, which is beneficial to cover the longer and colder winter nights. Temperature drops during the night are however detrimental. For traffic applications, the total light output of glow-in-the-dark road marks at the end of the night is not sufficient for the studied compound, although re-charging by the car's headlamps partially alleviates this. For energy storage applications, the trap density should be improved and tunneling recombination processes might be needed to overcome overnight temperature drops.

Light output measurements and computational models of microcolumnar CsI scintillators for x-ray imaging.

The authors report on measurements of light output and spatial resolution of microcolumnar CsI:Tl scintillator detectors for x-ray imaging. In addition, the authors discuss the results of simulations aimed at analyzing the results of synchrotron and sealed-source exposures with respect to the contributions of light transport to the total light output. The authors measured light output from a 490-μm CsI:Tl scintillator screen using two setups. First, the authors used a photomultiplier tube (PMT) to measure the response of the scintillator to sealed-source exposures. Second, the authors performed imaging experiments with a 27-keV monoenergetic synchrotron beam and a slit to calculate the total signal generated in terms of optical photons per keV. The results of both methods are compared to simulations obtained with hybridmantis, a coupled x-ray, electron, and optical photon Monte Carlo transport package. The authors report line response (LR) and light output for a range of linear absorption coefficients and describe a model that fits at the same time the light output and the blur measurements. Comparing the experimental results with the simulations, the authors obtained an estimate of the absorption coefficient for the model that provides good agreement with the experimentally measured LR. Finally, the authors report light output simulation results and their dependence on scintillator thickness and reflectivity of the backing surface. The slit images from the synchrotron were analyzed to obtain a total light output of 48 keV-1 while measurements using the fast PMT instrument setup and sealed-sources reported a light output of 28 keV-1 . The authors attribute the difference in light output estimates between the two methods to the difference in time constants between the camera and PMT measurements. Simulation structures were designed to match the light output measured with the camera while providing good agreement with the measured LR resulting in a bulk absorption coefficient of 5 × 10-5 μm-1 . The combination of experimental measurements for microcolumnar CsI:Tl scintillators using sealed-sources and synchrotron exposures with results obtained via simulation suggests that the time course of the emission might play a role in experimental estimates. The procedure yielded an experimentally derived linear absorption coefficient for microcolumnar Cs:Tl of 5 × 10-5 μm-1 . To the author's knowledge, this is the first time this parameter has been validated against experimental observations. The measurements also offer insight into the relative role of optical transport on the effective optical yield of the scintillator with microcolumnar structure.

On the Ce3+ → Cr3+ energy transfer in Lu3Al5O12 garnets

Two series of Lu3Al5O12:Cr3+ and Lu3Al5O12:0.5% Ce3+,Cr3+ luminescent materials were prepared by a sol–gel combustion method. All samples were characterized by powder X-ray diffraction (XRD), infrared (IR) and photoluminescence (PL) measurements. Moreover, luminous efficacies (LE), CIE 1931 colour points, and quantum efficiencies (QE) were calculated and discussed. Luminescence measurements indicated that Ce3+ ions located at Lu3+ site transfers absorbed energy to Cr3+ ions located at Al3+ site. However, with increasing Cr3+ concentration the total light output of Lu3Al5O12:0.5% Ce3+,Cr3+ phosphors decrease.