Karmann C. Mills

Nanomaterial registry: database that captures the minimal information about nanomaterial physico-chemical characteristics

Evaluating the implications of nanomaterials in biological and environmental systems can be difficult without sufficient characterization of the nanomaterials’ physico-chemical characteristics (PCC). Additionally, while nanomaterials possess inherent characteristics, their acquired characteristics can change based on the system under consideration or even the test method or protocol used for the characterization. The Nanomaterial Registry, an authoritative resource for nanomaterial data, has established minimal information about nanomaterials (MIAN) for PCC. The MIAN is used as a guideline for curating and archiving the nanomaterial information that is vital to understanding the biological and environmental implications of these materials. This manuscript details the MIAN developed and provides examples of curated data. The MIAN and Registry data model are flexible, and can accommodate new information and insights as scientific discovery regarding nanomaterials evolves. Through the use of the MIAN, the Registry archives sufficient metadata to allow the user to easily access the original/source study records of interest.

The Nanomaterial Registry: Facilitating the sharing and analysis of data in the diverse nanomaterial community

The amount of data being generated in the nanotechnology research space is significant, and the coordination, sharing, and downstream analysis of the data is complex and consistently deliberated. The complexities of the data are due in large part to the inherently complicated characteristics of nanomaterials. Also, testing protocols and assays used for nanomaterials are diverse and lacking standardization. The Nanomaterial Registry has been developed to address such challenges as the need for standard methods, data formatting, and controlled vocabularies for data sharing. The Registry is an authoritative, web-based tool whose purpose is to simplify the community’s level of effort in assessing nanomaterial data from environmental and biological interaction studies. Because the Registry is meant to be an authoritative resource, all data-driven content is systematically archived and reviewed by subject-matter experts. To support and advance nanomaterial research, a set of minimal information about nanomaterials (MIAN) has been developed and is foundational to the Registry data model. The MIAN has been used to create evaluation and similarity criteria for nanomaterials that are curated into the Registry. The Registry is a publicly available resource that is being built through collaborations with many stakeholder groups in the nanotechnology community, including industry, regulatory, government, and academia. Features of the Registry website (http://www.nanomaterialregistry.org) currently include search, browse, side-by-side comparison of nanomaterials, compliance ratings based on the quality and quantity of data, and the ability to search for similar nanomaterials within the Registry. This paper is a modification and extension of a proceedings paper for the Institute of Electrical and Electronics Engineers.

New understandings of failure modes in SSL luminaires

As SSL products are being rapidly introduced into the market, there is a need to develop standard screening and testing protocols that can be performed quickly and provide data surrounding product lifetime and performance. These protocols, derived from standard industry tests, are known as ALTs (accelerated life tests) and can be performed in a timeframe of weeks to months instead of years. Accelerated testing utilizes a combination of elevated temperature and humidity conditions as well as electrical power cycling to control aging of the luminaires. In this study, we report on the findings of failure modes for two different luminaire products exposed to temperature-humidity ALTs. LEDs are typically considered the determining component for the rate of lumen depreciation. However, this study has shown that each luminaire component can independently or jointly influence system performance and reliability. Material choices, luminaire designs, and driver designs all have significant impacts on the system reliability of a product. From recent data, it is evident that the most common failure modes are not within the LED, but instead occur within resistors, capacitors, and other electrical components of the driver. Insights into failure modes and rates as a result of ALTs are reported with emphasis on component influence on overall system reliability.

An efficiency-decay model for Lumen maintenance

Proposed is a multicomponent model for the estimation of light-emitting diode (LED) lumen maintenance using test data that were acquired in accordance with the test standards of the Illumination Engineering Society of North America, i.e., LM-80-08. Lumen maintenance data acquired with this test do not always follow exponential decay, particularly data collected in the first 1000 h or under low-stress (e.g., low temperature) conditions. This deviation from true exponential behavior makes it difficult to use the full data set in models for the estimation of lumen maintenance decay coefficient. As a result, critical information that is relevant to the early life or low-stress operation of LED light sources may be missed. We present an efficiency-decay model approach, where all lumen maintenance data can be used to provide an alternative estimate of the decay rate constant. The approach considers a combined model wherein one part describes an initial “break-in” period and another part describes the decay in lumen maintenance. During the break-in period, several mechanisms within the LED can act to produce a small (typically <; 10%) increase in luminous flux. The effect of the break-in period and its longevity is more likely to be present at low-ambient temperatures and currents, where the discrepancy between a standard TM-21 approach and our proposed model is the largest. For high temperatures and currents, the difference between the estimates becomes nonsubstantial. Our approach makes use of all the collected data and avoids producing unrealistic estimates of the decay coefficient.

Photoluminescent Nanofibers for Solid-State Lighting Applications

Photoluminescent nanofibers (PLN) can be formed by combining electrospun polymeric nanofibers and luminescent particles such as quantum dots (QD). The physical properties of PLNs are dependent upon many different nanoscale parameters associated with the nanofiber, the luminescent particles, and their interactions. By understanding and manipulating these properties, the performance of the resulting optical structure can be tailored for desired end-use applications. For example, the quantum efficiency of quantum dots in the PLN structure depends upon multiple parameters including quantum dot chemistry, the method of forming the PLN nanocomposites, and preventing agglomeration of the quantum dot particles. This is especially important in solution-based electrospinning environments where some common solvents may have a detrimental effect on the performance of the PLN. With the proper control of these parameters, high quantum efficiencies can be readily obtained for PLNs. Achieving high quantum efficiencies is critical in applications such as solid-state lighting where PLNs can be an effective secondary conversion material for producing white light. Methods of optimizing the performance of PLNs through nanoscale manipulation of the nanofiber are discussed along with guidelines for tailoring the performance of nanofibers and quantum dots for application-specific requirements.

The Nanomaterial Registry: Opportunities and challenges in informatics

The quantity of publicly available literature on nanotechnology is staggering. The interpretation, sharing and downstream analysis of the data in this literature is both complex and rapidly evolving. The complexities surrounding the research and data are largely a result of the characteristics inherent to nanomaterials, as well as the diverse test methods, protocols, and assays used to evaluate these characteristics and interactions. The Nanomaterial Registry (NR) has been developed, through cooperation with the nanomaterial community, to address challenges, such as the needs for standard protocols, methods, data formatting, and controlled vocabularies. The NR is an authoritative, web-based tool whose purpose is to simplify the communitys level of effort in assessing nanomaterial data from environmental and biological interaction studies. Because the NR is meant to be an authoritative resource, all data driven content is systematically curated and reviewed by subject matter experts. To support and advance nanomaterial research, a set of minimal information about nanomaterials (MIAN) has been developed and is foundational to the NR data model. The MIAN has been used to create evaluation and similarity criteria for nanomaterials that are curated into the NR. The NR is a publically available resource that is being built through collaborations with many stakeholder groups in the nanotechnology community, including industry, regulatory, government, and academia. Features of the NR website (www.nanomaterialregistry.org) currently include search, browse, side-by-side comparison of nanomaterials, compliance ratings based on the quality and quantity of data, and the ability to search for similar nanomaterials within the NR.

Reproducibility, sharing and progress in nanomaterial databases

Publicly accessible databases are core resources for data-rich research, consolidating field-specific knowledge and highlighting best practices and challenges. Further effective growth of nanomaterial databases requires the concerted efforts of database stewards, researchers, funding agencies and publishers.

Chromaticity Maintenance in LED Devices

With the recent improvements in LED luminous efficacy that have been achieved by the lighting industry, greater attention is being devoted to understanding the long-term performance of LEDs. Specifically, there is a need to understand and predict the ability of LEDs to maintain luminous flux and chromaticity over time. The issue of chromaticity maintenance (aka, chromaticity stability and color shift) is especially important for LED devices since they may be used for 10 years or more without replacement of the light source. The characteristics of LEDs have a significant impact on chromaticity maintenance for LED-based lamps and luminaires. However, other components of an LED device, including lenses, reflectors, and device design, can also have an impact on chromaticity. Understanding the aging characteristics of LEDs, lenses, and reflectors is critical to designing and building LED-based products for long-term use.

The Influence of Phosphor and Binder Chemistry on the Aging Characteristics of Remote Phosphor Products

The influence of phosphor and binder layer chemistries on the lumen maintenance and color stability of remote phosphor disks was examined using wet high-temperature operational lifetime testing (WHTOL). As part of the experimental matrix, two different correlated color temperature (CCT) values, 2,700 K and 5,000 K, were studied and each had a different binder chemistry. The 2,700 K samples used a urethane binder, whereas the 5,000 K samples used an acrylic binder. Experimental conditions were chosen to enable study of the binder and phosphor chemistries and to minimize photooxidation of the polycarbonate substrate. Under the more severe WHTOL conditions of 85 °C and 85% relative humidity (RH), absorption in the binder layer significantly reduced luminous flux and produced a blue color shift. The milder WHTOL conditions of 75 °C and 75% RH resulted in chemical changes in the binder layer that may alter its index of refraction. As a result, lumen maintenance remained high, but a slight yellow shift was found. The aging of remote phosphor products provides insights into the impact of materials on the performance of phosphors in an LED lighting system.

Assessing the reliability of electrical drivers used in LED-based lighting devices

Electrical components used in LED lighting devices have a significant impact on the reliability of lighting systems. Understanding the reliability of LED drivers requires a knowledge of the intended use of the device including environmental (e.g., temperature, humidity), electrical (i.e., voltage quality and transients), and mechanical (i.e., vibration) stresses that the products would experience. In addition, knowledge of the susceptibility of key electronic components (e.g., capacitors, switching transistors, diodes, ICs, and linear components) to these stresses is also important in understanding overall product reliability. Although this information is difficult to determine for an electronic assembly such as the LED lighting driver, accelerated tests can help provide insights regarding likely failure modes and provide a basis to project reliability and product lifetime. In this chapter we have investigated common failure modes in LED drivers under accelerated testing conditions.