Dy ^3+ single- and Dy ^3+ /Tb ^3+ double-doped LiAlB and BaB glasses are investigated for their external quantum efficiency under 452-nm excitation. In the case of double-doping, the energy transfer from Dy ^3+ to Tb ^3+ results in a combination of both Dy ^3+ - and Tb ^3+ -related emissions though Tb ^3+ cannot be excited directly at 452 nm. The energy transfer efficiency is obtained by deconvolution of the photoluminescence spectrum into the corresponding Dy ^3+ and Tb ^3+ components. There is, however, also an energy transfer from Tb ^3+ to Dy ^3+ which is confirmed by lifetime measurements.

Glass, in particular borate glass, is not only a very robust and hard material, but also offers good solubility for lanthanide ions. The lanthanide ions serve as luminescence centres in the glass system and emit a characteristic luminescence when excited by light in the ultraviolet/blue spectral range. The triply ionized lanthanide europium (Eu3+) enables a very intense red luminescence that is clearly visible even under strong contaminated conditions. Such luminescent glasses can be integrated into metallic tools for non-destructive, optical wear measurements. For this, the glass is incorporated into tool areas that are subject to abrasive wear. A key challenge of this approach is to match the hardness of the glass to that of the tool steel so that both have the same wear rate. In borate glass, this can be achieved by changing the ratio of network modifier to network former. Deep, converging holes are drilled into the tool and filled with an Eu3+-activated phosphor. As abrasion increases, the distance between the holes decreases. Measuring the distance between the red luminescent holes provides information about the degree of wear. The approach enables predictive maintenance, pre-vents tool failures and reduces production downtime, thereby increasing process reliability.

Lithium aluminoborate glass with different Li-to-(B+Al) ratios is investigated for mass density, Young’s modulus as well as indentation modulus and indentation hardness. The Young’s modulus is calculated based on the chemical composition and the experimental mass density. Both, density and modulus increase with network modifier (Li2O) content. Nanoindentation experiments show that indentation modulus and indentation hardness decline with decreasing Li-to-(B+Al) ratio. Furthermore, modulus and hardness decline significantly from the center to the edge of the sample due to slight compositional variations within the sample. These variations are probably caused by the inhomogeneous cooling during the glass-making process.

Thermal transient analysis (TTA) is a powerful technique for assessing thermal characteristics of electronic packages. However, commercial tools for TTA are often expensive and rely on proprietary solutions, limiting accessibility. This work presents a cost-effective and open-source approach for conducting high-resolution thermal transient measurements. It introduces the open-source Python package PyRth, which offers a cutting-edge thermal transient analysis toolkit. In addition, it demonstrates how general-purpose source measure units, such as the Keithley 2461, can be programmed with Lua-based scripts to perform complete thermal transient tests. The combination of open-source software and accessible hardware establishes a reproducible and customizable workflow for researchers and engineers, supporting integration into laboratory environments and industrial applications. Lastly, using the Least Absolute Shrinkage and Selection Operator (LASSO) for network identification by deconvolution is discussed.

The performance of luminescent light guides, i.e., the output-to-input ratio, the luminous flux, and the color impression at the output face, is investigated with the help of ray-tracing simulations. Apart from the light guide length, two different output faces are analyzed in detail: a rough and a pyramidally-structured one. Light guides based on Dy3+ single-and Dy3+/Tb3+ double-doped BaB glass are compared for their potential as blue-to-green light converters, in particular for the light yield in the green spectral range. For a rough output face, the color impression depends significantly on the light guide length due to color mixing of excitation and luminescence light. Incase of a pyramidally-structured output face, the excitation light is totally reflected and only the generated luminescence light can leave the light guide. The pyramidal structure enables an efficient blue-to-green conversion for significantly shorter light guides.

Polylactide (PLA) represents a sustainable alternative to common optical polymers in lighting applications. However, its application temperature is currently limited, since the material crystallizes and becomes cloudy when exposed to temperatures above 55-65 °C. Here, N,N'-ethylenebis(stearamide) and N,N'-ethylenebis(12-hydroxystearamide) are applied as clarifiers, and their effects are known for foils. This approach is extended to bulky materials (d = 1.5 mm). Optical characterization was complemented by microscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Additionally, NMR was applied to understand the effects of the fatty acid amides on a molecular level. All methods confirm the nucleating effects of both additives, while the crystallinity and crystal structure remain unchanged. A controlled crystallization at lower temperatures is discovered to promote the effect of the clarifiers by further reducing crystallite size. Finally, the crystallized samples are exposed to 80 °C and found to maintain high optical transmission. A tempering step at low temperatures is suggested to maximize clarifying effects.

For transient thermal analysis, network identification by deconvolution (NID) is a well-known method. This paper explores the Lanczos-based alogorithm within the Foster-to-Cauer transformation. This substep has not been rigorously tested and compared to alternative approaches as part of NID yet. This work completes this aspect, providing an in-depth examination of Lanczos’ approach as well as discussing specific optimizations for NID. The use of double-precision arithmetic makes Lanczos’ method relatively fast. However, as it is approximate, derived results such as the differential structure function require additional noise reduction procedures. Implementation instructions and computational time complexity are provided as well as an application to a 36-LED test boards as an example of industry-scale pulsed transient thermal analysis. In total, Lanczos’ method is shown to be a robust alternative to existing methods, providing computationally efficient results.

Thermal transients of small or thermally well-conducting components typically relax with a very short time constant. In some cases, the fastest changes occur on a time scale of a few tens to hundreds of microseconds. Providing a sampling rate higher than 1 kHz is challenging, even for modern infrared cameras. This work presents a periodic non-uniform sampling technique for measuring thermographic transients, which increases the effective sampling rate by one order of magnitude to 10 kHz, resulting in a temporal resolution of 100 μs. The practical application of this technique captures parts of the thermal transient that would otherwise be missed for standard sampling rates. The results confirm the algorithm’s ability to enhance the effective sampling rate, providing a more detailed thermal analysis of rapid transient processes in small-scale electronic components.

Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types of commercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank's optical properties accounting for uncertainties exceeding 20%.

With decreasing electric components sizes, heat management becomes a more challenging part in electronic engineering. In addition, project timelines are compressed, giving less time for multiple loops and iterations. This pressures temperature measurements to be fast, comprehensive, and accurate. With its contactless and spatially-resolved characteristics, thermography is a valuable technique to provide measurements for thermal analysis of complex circuits. Opportunities for optimization are found in providing high temporal and spatial resolution simultaneously. This study presents a sampling technique, so-called super-frequency sampling, that significantly increases the temporal resolution without decreasing spatial resolution for thermal transient analysis. The principle is demonstrated by tests on a high-power LED. The results indicate an increased sampling frequency by almost a factor of ten.

Effective temperature measurements are crucial for optimizing the design and performance of LEDs. This study presents a comprehensive investigation of LED temperature assessment using thermographic, electric, and spectral techniques. The complex thermal interactions within LEDs, such as the impact of phosphor layers and fill-in materials, pose challenges for accurate measurements. Thermography, while effective for LEDs with phosphor, faces limitations for phosphor-less LEDs due to low emissivities. To address this, an approach involving an optically-transparent infrared-opaque coating is proposed, demonstrated by tests on a thin film. This coating holds promise for improved thermographic measurements. In addition, spectral analysis of LED emission spectra reveals the potential to extract accurate temperatures for phosphor layers based on observed spectral shifts. Overall, this study advances LED temperature measurement methods, offering insights for enhanced accuracy and reliability in LED thermal analysis.

Silicon-air batteries are candidates for next generation batteries from non-critical raw materials. However, current silicon-air batteries with alkaline electrolytes suffer from premature termination of the discharge process. To understand this process, we investigated the correlation of dissolved silicon in the electrolyte and the discharge duration until passivation. The air- and Si-electrode could be excluded as the source of the voltage drop, while the concentration of silicates in the electrolyte was identified as the decisive factor. A low silicate concentration in the electrolyte was found to be crucial for a sustained discharge of silicon-air batteries with alkaline electrolytes and full consumption of the silicon electrode used in these conditions was shown.

Silicon–air batteries (SABs) are attracting significant attention for their potential as high‐energy‐density electrochemical storage devices. One of the main limitations for the commercial use of alkaline SABs is the high corrosion, which results in a low conversion efficiency. Herein, the aim is to examine the influence of polyethylene glycol (PEG) on the conversion efficiency of SABs, shedding light on key factors affecting their performance. SABs using KOH as electrolyte at two concentrations, 0.5 and 2.0 mol L−1, are investigated. The results show that replacing part of the water in the alkaline electrolyte with PEG changes the etching behavior from anisotropic to polishing and increases the specific energy density by 53% and 123% in 0.5 and 2 mol L−1 KOH electrolytes, respectively.

For a thermal analyst, the evaluation of structure functions is as a powerful technique to optimize heat transfer processes and to study thermal phenomena. The Optimization-based Network Identification (ONI) offers an alternative approach to construct structure functions, complementing existing methods for thermal transient analysis. The accuracy of ONI in modeling thermal transients is investigated in this study. The method is rigorously compared with a self-implemented variant of Network Identification by Deconvolution (NID) and the widely used implementation of NID in the Siemens Simcenter T3ster Master. While ONI encounters challenges in heat paths with pronounced heat spreading effects, its implicit modeling of structure functions aids in determining partial thermal resistances. In conclusion, ONI’s precision and convergence quality offer a promising way to comprehend thermal dynamics in semiconductor devices.

The demand for electronic devices with high storage capacities and long-lasting batteries has motivated the development of new battery systems. Metal-air and semiconductor-air batteries are particularly interesting due to their high capacity densities due to the use of air for the cathode reaction. The Si-air battery was introduced as a battery system that operated with a room-temperature ionic liquid or KOH as the electrolyte. [1,2] However, the practical capacity density is reduced to a fraction of the theoretical value in liquid electrolytes, and the passivation of the silicon anode in aqueous electrolytes is a major challenge. [3,4] Increasing the surface area of the Si electrode can reduce the local reaction rate and enable the dissolution of the reaction products, but it also increases the overall corrosion rate. A threshold temperature and the addition of fresh electrolyte solution can also extend the discharge duration. [3,5] Silicon-air batteries have the potential to become the next generation of batteries, as they are made from non-critical raw materials and have a high theoretical capacity. However, silicon-air batteries using alkaline electrolytes suffer from early passivation and termination of discharge. To understand this process, we investigated the correlation between dissolved silicon in the electrolyte and the discharge duration until passivation. Our findings revealed that silicate enrichment in the electrolyte reduces the flow of reaction products away from the silicon surface, leading to rapid oxidation and passivation of the surface. [6] We utilized various techniques, including electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), to investigate this phenomenon further. Our results showed that the silicate concentration in the electrolyte plays a crucial role in determining the performance of silicon-air batteries. A lower concentration of silicates in the electrolyte leads to sustained discharge, while a higher concentration results in early passivation and termination of discharge. In conclusion, our investigation highlights the critical role of silicates in the performance of silicon-air batteries utilizing alkaline solutions. Our findings suggest that controlling the concentration of silicates in the electrolyte is crucial to ensure the sustained discharge of these batteries. This study provides essential insights into the mechanisms governing the passivation of silicon surfaces in alkaline electrolytes, which will aid in the development of more efficient and sustainable energy storage solutions. [1] G. Cohn, D. Starosvetsky, R. Hagiwara, D. D. Macdonald, Y. Ein-Eli, Electrochem. commun. 2009 , 11 , 1916–1918. [2] X. Zhong, H. Zhang, Y. Liu, J. Bai, L. Liao, Y. Huang, X. Duan, ChemSusChem 2012 , 5 , 177–180. [3] Y. E. Durmus, Ö. Aslanbas, S. Kayser, H. Tempel, F. Hausen, L. G. J. G. J. de Haart, J. Granwehr, Y. Ein-Eli, R.-A. A. Eichel, H. Kungl, Electrochim. Acta 2017 , 225 , 215–224. [4] Y. E. Durmus, S. Jakobi, T. Beuse, Ö. Aslanbas, H. Tempel, F. Hausen, L. G. J. de Haart, Y. Ein-Eli, R.-A. Eichel, H. Kungl, J. Electrochem. Soc. 2017 , 164 , A2310–A2320. [5] S. Sarwar, M. Kim, G. Baek, I. Oh, H. Lee, Bull. Korean Chem. Soc. 2016 , 37 , 997–1003. [6] R. Schalinski, S. L. Schweizer, R. B. Wehrspohn, ChemSusChem 2023 , DOI 10.1002/cssc.202300077.

Dy3+ and Tb3+ single- and double-doped barium borate glasses are investigated for their luminescence properties. Their potential as luminescent light guide is evaluated on the basis of ray-tracing simulations. Transmission, photoluminescence, and quantum efficiency measurements serve as input data. The luminous flux at the end of the light guide depends significantly on its length as well as on the surface properties. The best results are obtained for light guides with the side faces coated with a 100 % reflecting mirror and a rough output face with Lambertian scattering characteristics. For an excitation wavelength of 452 nm, the color impression at the end of a Dy3+/Tb3+ double-doped light guide shifts from blue for very short light guides via white for medium-size light guides to green-yellowish for relatively long light guides.

In this work, an evaluation method for transient thermal measurements is presented. It allows for a high temporal sensitivity by analysing the spectral composition of a thermal transient, the so-called time constant spectrum. The spectral components provide a detailed insight into the heat flow dynamics and thermal parameters describing a multi-layer system. The method is based on a one-dimensional heat path analysis technique common for the thermal characterisation of electronic components, called ‘network identification by deconvolution’. Here, a generalisation, called ‘thermographic network identification’, is presented to obtain spatially resolved thermal equivalence networks as complete thermal model of the device under study. As a proof of concept, two samples are investigated. The method is discussed on the basis of the obtained results.

In this work, single- and double-doped Dy3+ and Tb3+ barium borate glasses are investigated for their potential as light converters. The density and the absorption coefficient show linearly increasing trends with an increasing lanthanide content. The external quantum efficiency of the double-doped samples is a combination of the respective single-doped samples. The strong energy transfer from Dy3+ to Tb3+ results in an intense Tb3+-related emission, i.e., an intense green luminescence. Thus, excitation at a Dy3+-related wavelength of 452 nm enables a Tb3+-related emission, at which a single-doped Tb3+ sample barely shows any luminescence. Lifetime measurements show that there is not only an energy transfer from Dy3+ to Tb3+, but also vice versa.

The calculation of accurate and detailed structure functions is crucial to perform a reliable thermal transient analysis using tools such as the differential structure function or local thermal resistance diagram. This study investigates six different Foster-to-Cauer transformation methods for Network Identification by Deconvolution (NID) including Codecasa’s approach and Fernando’s approach. Four of the presented algorithms (Khatwani, Sobhy, de Boor and Golub, polynomial long division) are evaluated with respect to numerical precision and computation time as a function of network length. Results reveal that Sobhy’s approach offers significantly more efficient computations, particularly for longer networks. In these cases, the faster Foster-to-Cauer transformation offers a reduction in total computation time of NID by more than a factor of four. Structure functions with more than 1200 points are calculated in approximately 30 s.

Luminescent light guides on the basis of barium borate glass are studied. The light guides are optically-activated with different amounts of trivalent terbium ions. Absorption coefficient, photoluminescence quantum efficiency, as well as photoluminescence emission spectra from reference samples serve as input data for ray-tracing simulations. The simulations yield an optimum light guide length of approximately 50mm with the side faces of the light guide coated with a 100% reflecting mirror and a rough output face with Lambertian scattering characteristic. The input face is a half-transmitting mirror which is transmissive for the excitation wavelength of 378nm but reflective for the emission bands in the visible spectral range. For a light guide with a Tb3+ content of 1.77at.%, a luminance of more than 60cd/mm2 is predicted for an excitation power density of 1W/mm2.