Total Light Output Research Articles

X-ray detection capability of a Cs2ZnCl4 single-crystal scintillator

The X-ray detection capability of a scintillation detector equipped with a Cs2ZnCl4 single crystal was evaluated. The scintillation decay kinetics can be expressed as the sum of two exponential decay components. The fast decay component had a decay time constant of 1.8 ns, and its relative intensity was 95%. The total light output was 630 photons/MeV, and a subnanosecond timing resolution of 0.66 ns was obtained. The detection efficiency of 67.4 keV X-rays was 80% for a detector equipped with a 2.2-mm-thick Cs2ZnCl4 crystal. Thus, excellent timing resolution and high detection efficiency were achieved simultaneously.

Temperature dependence of BCF plastic scintillation detectors

We examined temperature dependence in plastic scintillation detectors (PSDs) made of BCF-60 or BCF-12 scintillating fiber coupled to optical fiber with cyanoacrylate. PSDs were subjected to a range of temperatures using a temperature-controlled water bath and irradiated at each temperature while either the dose was measured using a CCD camera or the spectral output was measured using a spectrometer. The spectrometer was used to examine the intensity and spectral distribution of scintillation light emitted by the PSDs, Cerenkov light generated within the PSD, and light transmitted through an isolated optical coupling. BCF-60 PSDs exhibited a 0.50% decrease and BCF-12 PSDs a 0.09% decrease in measured dose per °C increase, relative to dose measured at 22 °C. Spectrometry revealed that the total intensity of the light generated by BCF-60 and BCF-12 PSDs decreased by 0.32% and 0.13%, respectively, per °C increase. The spectral distribution of the light changed slightly with temperature for both PSDs, accounting for the disparity between the change in measured dose and total light output. The generation of Cerenkov light was temperature independent. However, light transmitted through optical coupling between the scintillator and the optical fiber also exhibited temperature dependence.

Using Lenses to Improve the Output of a Patterned Luminescent Solar Concentrator

AbstractPrevious work demonstrated that reabsorption, a major loss mechanism in luminescent solar concentrators (LSCs), could be reduced by patterning luminescent dyes on the device surface; emission efficiency improved considerably. However, total light output decreased due to reduced absorption of the incident light. The results of adding a (poly)carbonate lens system to a patterned waveguide to focus more of the incident light on the line patterns are presented in this work. We demonstrate a set of parameters wherein a patterned LSC with lens system on a white background can outperform a standard fully‐covered waveguide using a similar scatterer.

Experimental and theoretical studies of donor–acceptor scintillation from PbI2

We report on the scintillation properties of undoped PbI2, and PbI2 doped with La, Cu, Ag, and Te. X-ray luminescence spectra were recorded at 7K and the time responses for 80ps pulses of X-rays were recorded from 14K to 150K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000μm in size. We found that at 14K the undoped samples had a fast emission at 520nm (0.18eV below the band edge) and a total light output of about 40,000photons/MeV. 10% of this light appears in the first ns, which is 5 times greater than LSO and 1.5 times greater than LaBr3:Ce. 50% of the light appears in the first 100ns. The luminosity decreased dramatically as the temperature was increased above 40K, consistent with a non-radiative path that has an activation energy of 3.8meV. Doping with the donor La3+ only slightly changed these scintillation properties. Doping with the donor La3+ and the deep acceptors Cu+, Ag+, and Te2– produced primarily slow donor–acceptor emissions at peak wavelengths of 605, 653, and 800nm, respectively. The luminosity of the samples doped with La3+ and Cu+ depended strongly on the La3+ concentration, demonstrating its role as an electron donor. First-principles band structure calculations showed (1) that the donor level depth of an isolated iodine vacancy is about 0.8eV, too deep to explain the 520nm emission wavelength, and (2) that a donor–acceptor pair consisting of a spatially associated iodine vacancy donor and a lead vacancy acceptor has shallower donor and acceptor depths that are consistent with the 520nm emission wavelength.

Sensitive chemiluminescent immunoassay of triclopyr by digital image analysis

An image based detection of chemiluminescence enzyme-linked immunosorbent assay (CL-ELISA) for the quantification of triclopyr has been developed. The immunoassay was an indirect competitive immunoassay with an anti-rabbit secondary antibody conjugated to horseradish peroxidase (HRP). Chemiluminescence was produced by the luminol/H2O2/HRP reaction, detected by a monochrome video CCD camera and digitized with an Imagraph IC-PCI frame grabber using a custom program developed in C++ (Microsoft Visual C++ 6.0). Two main improvements are reported in the data processing software: the implementation of a circular mesh covering the perimeter of each well, eliminating diffuse light from the neighboring wells, and the use of volume (the integration of light intensity of all pixels that define a well) as an analytical signal instead of CL intensity or area (as usual in commercial plate readers) to improve precision for normalization of the total light output. The standard curve was produced for 0.01–10ng/L triclopyr. The limit of detection was 0.8ng/L and the variation coefficient was 3.07% (n=10, P=0.05).

X-ray detection capability of a BaCl2 single crystal scintillator

The x-ray detection capability of a scintillation detector equipped with a BaCl2 single crystal was evaluated. The scintillation decay kinetics can be expressed by a sum of two exponential decay components. The fast and slow components have lifetimes of 1.5 and 85 ns, respectively. The total light output is 5% that of YAP:Ce. A subnanosecond timing resolution was obtained. The detection efficiency of a 67.41 keV x-ray is 87% for a detector equipped with a BaCl2 crystal 6-mm thick. Thus, excellent timing resolution and high detection efficiency can be simultaneously achieved. Additionally, luminescence decay characteristics under vacuum ultraviolet excitation have been investigated. Radiative decay of self-trapped excitons is thought to be responsible for the fast scintillation component.

Chemiluminescence from alkoxy-substituted acridinium dimethylphenyl ester labels

Chemiluminescent acridinium dimethylphenyl ester labels are used in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered by alkaline peroxide in the presence of the cationic surfactant cetyltrimethylammonium chloride (CTAC). The surfactant plays a critical role in the chemiluminescence process of these labels by both accelerating their emission kinetics and increasing total light output enabling high throughout and improved assay sensitivity in automated immunoassays. Despite the surfactant's crucial role in the chemiluminescent reaction, no study has investigated how structural perturbations in the acridinium ring could impact the influence of the surfactant. We describe herein the synthesis and properties of three new alkoxy-substituted, acridinium dimethylphenyl esters where the nature of the alkoxy group in the acridinium ring was varied (hydrophobic or hydrophilic). Chemiluminescence measurements of these alkoxy-substituted labels indicate that hydrophilic functional groups in the acridinium ring, in particular sulfobetaine zwitterions, disrupt surfactant-mediated compression of emission times but not enhancement of light yield. These results support the hypothesis that surfactant-mediated effects require the binding of two different reaction intermediates to surfactant aggregates and, that surfactants influence light emission from acridinium esters by two separate mechanisms. Our studies also indicate that preservation of both surfactant effects on acridinium ester chemiluminescence and low non-specific binding of the label can be achieved with a relatively hydrophobic acridinium ring coupled to a hydrophilic phenolic ester leaving group.

Thermal management of LED‐LCD TV display

Abstract— In the past years, the thermal management of the LEDs in an LCD TV with an LED backlight has evolved to cater to steadily increasing power densities in ever thinner product enclosures. In the lighting and computer industry, solutions to comparable thermal challenges are based on the use of large‐finned heat sinks. In the thin form factor of a modern TV set, this is not feasible, and the only large surface areas available for cooling are located on the front and the back of the TV set. The role of the in‐plane spreading has not been addressed thus far. The scope of the present work is to clarify the thermal significance of heat spreading in the in‐plane direction in the set, especially in relation to cost down through the use of less LED packages at equal total light output.

25.3: LED Array with Recycling for High‐Power Projector Applications

AbstractLEDs are still not bright enough, compared to arc lamps, for high power projector applications. For high power applications, multiple LEDs are required to increase the total light output with the same amount of increase in etendue. Even with the use of larger imaging panels with larger etendue values, the total output of the LED projector is still not sufficient for cinema projection applications. With recycling technology, the etendue of the LED can be reduced with increased brightness. This paper describes two systems with an array of 7 LEDs with recycling, such that the combined etendue matches with standard imagers for cinema projector applications. The first system uses a single array of 7 white LEDs with up to 9,500 lumens of white light can be generated at an etendue of 70, which is the etendue value of standard cinema projector systems. A screen lumen of over 3,300 lumens can be achieved. The second system uses 3 independent arrays of 7 red, green and blue LEDs combined producing to 18,500 lumens of white light at an etendue of 70. A screen lumen of over 6,500 lumens can be achieved from a single projector. Using two such projectors with combined output of over 13,000 lumens, the system can be used in small cinema replacing xenon based system or laser based systems.

Effect of surfactants on the chemiluminescence of acridinium dimethylphenyl ester labels and their conjugates

Chemiluminescent acridinium dimethylphenyl esters, containing two methyl groups flanking the phenolic ester bond, display excellent chemiluminescence stability and are used as labels in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of the cationic surfactant cetyltrimethylammonium chloride. Under these conditions, light emission is rapid and is complete in <5 s. In the present study we examined the effect of various surfactants on light emission from acridinium dimethylphenyl ester labels and their conjugates containing hydrophilic linkers derived either from hexa(ethylene)glycol or a sulfobetaine zwitterion. Sulfobetaine zwitterions are very polar and incorporation of these functional groups in acridinium dimethyphenyl esters and their conjugates represents a new approach to improving the aqueous solubility of these chemiluminescent labels. Our results indicate that in general, surfactants affect light emission from these labels and their conjugates by two discrete mechanisms. Cationic surfactants, but not anionic or non-ionic surfactants, accelerate overall light emission kinetics and a more modest effect is observed with zwitterionic surfactants. Surfactants also enhance total light output and the magnitude of this enhancement is maximal for cationic surfactants and a sulfobetaine zwitterionic surfactant. These observations are the first to clearly delineate the role of the surfactant on the chemiluminescence reaction pathway of acridinium esters and can be rationalized based on known effects of surfactant aggregates on bimolecular and unimolecular reactions.

Interplay of cavity thickness and metal absorption in thin-film InGaN photonic crystal light-emitting diodes

Thin-film InGaN photonic crystal (PhC) light-emitting diodes (LEDs) with a total semiconductor thickness of either 800 nm or 3.45 μm were fabricated and characterized. Increased directional radiance relative to Lambertian emission was observed for both cases. The 800-nm-thick PhC LEDs yielded only a slight improvement in total light output over the 3.45-μm-thick PhC LEDs. Simulations indicate that, except for ultrathin devices well below 800 nm, the balance between PhC extraction and metal absorption at the backside mirror results in modal extraction efficiencies that are almost independent of device thickness, but highly dependent on mirror reflectivity.

Optimization of a LSO-Based Detector Module for Time-of-Flight PET

We have explored methods for optimizing the timing resolution of an LSO-based detector module for a single-ring, "demonstration" time-of-flight PET camera. By maximizing the area that couples the scintillator to the PMT and minimizing the average path length that the scintillation photons travel, a single detector timing resolution of 218 ps fwhm is measured, which is considerably better than the ~385 ps fwhm obtained by commercial LSO or LYSO TOF detector modules. We explored different surface treatments (saw-cut, mechanically polished, and chemically etched) and reflector materials (Teflon tape, ESR, Lumirror, Melinex, white epoxy, and white paint), and found that for our geometry, a chemically etched surface had 5% better timing resolution than the saw-cut or mechanically polished surfaces, and while there was little dependence on the timing resolution between the various reflectors, white paint and white epoxy were a few percent better. Adding co-dopants to LSO shortened the decay time from 40 ns to ~30 ns but maintained the same or higher total light output. This increased the initial photoelectron rate and so improved the timing resolution by 15%. Using photomultiplier tubes with higher quantum efficiency (blue sensitivity index of 13.5 rather than 12) improved the timing resolution by an additional 5%. By choosing the optimum surface treatment (chemically etched), reflector (white paint), LSO composition (co-doped), and PMT (13.5 blue sensitivity index), the coincidence timing resolution of our detector module was reduced from 309 ps to 220 ps fwhm.

Many facets of light pollution

Luginbuhl, Walker, and Wainscoat reply: We appreciate the concern of Mark Rea, John Bullough, and Jennifer Brons for aspects of light pollution other than sky glow, and we support increased awareness and reduction of all forms of light pollution and energy waste. Our article was explicitly about the impacts on astronomical observatories and science, though to a large extent the careless lighting practices that increase sky glow over observatories also cause light trespass, glare, and energy waste. Nevertheless, many techniques used to protect observatories, in particular the full shielding of fixtures to control direct uplight, have wide applicability for national parks, coastlines, and anywhere citizens want to preserve or restore their ability to see stars in the night sky.Of course, distance and lighting amounts are critical factors. If direct uplight were a tiny fraction of total light output, approaches other than improving shielding might be more productive for reducing sky glow. But the observational evidence does not support the low uplight fraction Rea and coauthors suggest. Using measurements of how sky glow varies with distance and inventories of light fixtures, other researchers find uplight percentages of 8-15%. 1–3 1. R. H. Garstang, Publ. Astron. Soc. Pac. 98, 364 (1986).2. P. Cinzano, Mem. Soc. Astron. Ital. 71, 113 (2000).3. C. B. Luginbuhl et al., Publ. Astron. Soc. Pac. 121, 185 (2009). So direct upward emission, whatever the distance or amount, dominates sky glow. Eliminating it in communities with typical shielding and near-ground blocking would reduce sky glow by 35-75% for observation distances of 50-200 km.The writers’ suggestion that vegetation could be intentionally used to decrease light pollution impacts may have some merit, though vegetation is not something on which astronomers or lighting designers have much influence. In any case, the modeling shows that the impact of direct upward emissions remains disproportionate even in the presence of substantial blocking by structures or vegetation.Whatever uses the outdoor site-lighting performance metric may have for evaluating other aspects of light pollution, it is not a good metric for evaluating sky glow. It contains no information about the direction light is propagating away from a lighting installation, nor does it distinguish between upward- and downward-directed light. As our work and that of others 1 1. R. H. Garstang, Publ. Astron. Soc. Pac. 98, 364 (1986). , 2 2. P. Cinzano, Mem. Soc. Astron. Ital. 71, 113 (2000). , 4 4. P. Cinzano, F. J. Diaz-Castro, Mem. Soc. Astron. Ital. 71, 251 (2000). demonstrate, direction is critical in considering most aspects of light pollution.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. R. H. Garstang, Publ. Astron. Soc. Pac. 98, 364 (1986). Google ScholarCrossref, ISI2. P. Cinzano, Mem. Soc. Astron. Ital. 71, 113 (2000). Google Scholar3. C. B. Luginbuhl et al., Publ. Astron. Soc. Pac. 121, 185 (2009). Google ScholarCrossref, ISI4. P. Cinzano, F. J. Diaz-Castro, Mem. Soc. Astron. Ital. 71, 251 (2000). Google Scholar© 2010 American Institute of Physics.

Abstract 5242: Bioluminescence imaging of radiation induced tumor growth inhibition in orthotopic mouse models

Abstract Introduction: Radiation therapy continues to be a standard of care for many cancer indications including brain and prostate. Commonly, strategies for development of new chemotherapies encompass intended combination therapy with radiation. Preclinical methods for using localized radiation therapy against tumors in specific tissues may increase clinical relevance and predictive power of the models. The ability to non-invasively detect tumor burden and radiation response in deep tissue tumors would be an additional advantage. We describe application of localized radiation therapy in two orthotopic tumor models with parallel luciferase driven imaging of tumor burden and response. Methods: Human prostate and brain tumor cell lines transfected to constitutively express luciferase were used in these studies. For the prostate orthotopic, PC-3M-luc-C6 prostate carcinoma cells (5 × 105 cells in 20µl) were injected into the dorsal prostatic lobe of male nu/nu mice on Day 0. For the brain orthotopic, U87MG-luc glioma cells (106 cells in 10µl) were injected by stereotax 2mm right lateral and 1mm anterior to the coronal suture at a depth of 2mm. At staging (prostate: Day 7; brain: Day 27) animals were injected with 150mg/kg luciferin and imaged using bioluminescence. The tumors were segmented and total light output in photons/sec used to quantify tumor burden and select mice to go into two groups (prostate: n=10; brain: n=8) matched for mean tumor burden. In each case, Group 1 was untreated and Group 2 was treated using 2.5 Gy radiation (QDx5; 2 off) x2wk, with a lead shielded holder used to localize the dose to the prostate or brain regions. Bioluminescence imaging was used to assess tumor burden and treatment response over time in each model. Results and Discussion: Radiation therapy at 15 Gy on a (QDx5;2off)x2wk schedule was tolerated, producing 3% and 13% mean body weight loss in the prostate and brain tumored mice respectively. Bioluminescence imaging enabled a highly sensitive and quantitative end point for tumor burden in both cases, and highlighted localization of the tumor growth to the tissues in question. The treatments resulted in significant tumor growth inhibition compared with controls. Radiation resulted in approximate tumor stasis in both cases, with T/C values of 6% (4 weeks post-Rx) and 43% (1 week post-Rx) in the prostate and brain tumor models, respectively. The luciferase based imaging approach coupled with localized radiation treatment enables a quantitative model for deep tissue tumor targeted combination chemotherapy/radiation treatment strategies in preclinical models. This approach may facilitate development of new molecules for future use with radiation, including optimization of schedule and timing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5242.

Performance of ‘energy efficient’ compact fluorescent lamps

Background: Compact fluorescent lamps (CFLs) have been heralded as highly energy efficient replacements for incandescent light globes, however, there is some public dissatisfaction with the light output and colour of CFLs. Independent examination of the claims made has not been made. Compliance with the interim Australian/New Zealand Standard has not been established by any independent authority. While the total light output (luminous flux) may meet certain standards, luminous intensity distributions of some designs do differ significantly from the incandescent sources that they are intended to replace.Methods: Luminous intensity distribution, luminous flux and spectral energy distribution of CFLs claimed to be equivalent to 75-W incandescent globes and 75-W incandescent globes (pearl and clear) were measured. Luminous flux, luminous efficacy, colour rendering index, correlated colour temperature, wattage and power factor were then calculated and compared with claims made by manufacturers and requirements of the standards.Results: The sources generally complied with the requirements for luminous flux, luminous efficacy, colour rendering index and correlated colour temperature. The claim of 75-W equivalence, which is not regulated in Australia and New Zealand, is justified less than half the time. Luminous intensity distributions of biaxial CFLs are distinctly different from the incandescent lamps they purport to replace.Conclusion: CFLs generally comply with the standards set. The basis on which equivalent wattages are claimed needs to be included in the Australian and New Zealand standard because this is the measure most likely to be relied on by the public. Due to the differences in luminous intensity distribution, CFLs may not necessarily be a direct replacement for incandescent sources without some consideration.

Stereoscopic projector for polarized viewing with extended color gamut

Stereoscopic projectors show left and right eye information to induce a sense of depth. The viewer wears eyeglasses that separate the left and right eye images using color, shutters or polarization mechanisms. Polarization-based systems can use two identical projectors with passive polarizers at the output of their projection lens. We have designed and built a prototype of a stereoscopic projection system that incorporates the functionality of both projectors and polarizers into one optical engine. Furthermore, the system is adapted to incorporate large color gamut visualization with up to six primary colors. Light emitting diodes with different colors are used as light sources. The optical engine uses two liquid crystal on silicon light modulators to simultaneously modulate one s- and one p-polarized image. Both modulation light paths in the optical engine have a throughput of 10% yielding a total throughput of 20%. In red, green and blue color operation we demonstrate stereoscopic vision wearing polarization sensitive eyeglasses with a 40% increase of the ITU-R BT.709 color space. The images are shown at a frame rate of 120 Hz, producing a total light output of 25 lm, a contrast of 1000:1 and 0.5% crosstalk. We also demonstrate that cyan-colored information can be modulated by the system, which results in a 50% increase of the ITU-R BT.709 color space.

BaBrI:Eu 2+, a new bright scintillator

The scintillation properties of BaBrI:Eu 2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Excellent scintillation properties were measured. A light yield of 81,000±3000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 4.8±0.5% was observed for the 662 keV full absorption peak. Pulsed X-ray luminescence measurements show two exponential decay components of 297 and 482 ns with a contribution to the total light output of 23% and 77%, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband center at 413 nm. These initial values make BaBrI:Eu 2+ one of the brightest and the fastest known Eu 2+-doped scintillators.

Eu 2+-doped Ba 2CsI 5, a new high-performance scintillator

The crystal growth and scintillation properties of Ba 2CsI 5:Eu 2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Ba 2CsI 5:Eu 2+ presents excellent scintillation properties. An estimated light yield of 97,000±5,000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 3.8±0.3% was observed for the 662 keV full absorption peak. Pulsed X-ray luminescence measurements show a relatively complex time response with four exponential decay components of 48,383, 1500 and 9900 ns with a contribution to the total light output of 1%, 26%, 68% and 25%, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband centered at 2.85 eV. First principles calculations show strong localization of the excited state on the Eu site. Ba 2CsI 5:Eu 2+ has a density of about 5 g/cm 3. These first reported scintillation properties make Ba 2CsI 5:Eu 2+ a very high-performance scintillator.

Application of Nanosphere Lithography to LED Surface Texturing and to the Fabrication of Nanorod LED Arrays

In this study, the process of nanosphere lithography was developed and applied to LED surface texturing and nanorod device fabrication. We observed a texture-size-dependent improvement of total light output. While the increase of output optical power from the textured LEDs can be attributed to surface roughening in the GaN-air surface and to the increase of internal quantum efficiency as the strain is relaxed with the surface texturing, the size-dependent device performance is related to the interaction of generated photons with the textured surface. We further etched through the p-GaN and quantum well region to form p-i-n nanorods on the sample. By inserting a spacer to prevent p-type contact from shorting the n-GaN, we successfully demonstrated nanorod LED arrays. For such a device, a narrower radiation profile was demonstrated from the nanorod LED array as compared with that from the planar LED. The result is associated with the vertical guiding effect along the nanorod cylinder and the Bragg scattering of photons extracted from the sidewall by the rest of the rods. Furthermore, the electroluminescence spectra showed a nearly constant peak wavelength of the nanorod LED arrays, which is due to the suppression of the effect of quantum confined Stark effect.

Enhancement of Light Extraction Efficiency Using Lozenge-Shaped GaN-Based Light-Emitting Diodes

We have demonstrated both theoretically and experimentally that a lozenge-shaped light-emitting diode (LED) enhances light extraction efficiency compared with a conventional rectangular LED. The total light output power of the lozenge-shaped LED on a transmitter optical can (TO-can)-type package shows an increase of 12% at an injection current of 20 mA when compared with that of a rectangular LED. Moreover, the series resistance and the forward voltage of the lozenge-shaped LED slightly decrease compared with those of the rectangular LED. The far-field emission pattern shows that the light escaping from the lozenge-shaped LED along the horizontal direction is larger than that from the rectangular LED.