Light emitting diodes and the lighting revolution: The emergence of a solid-state lighting industry

Fabrication of white light emitting diodes via high yield surface passivated carbon quantum dots doped with terbium

Exploiting the unique characteristics of various materials to create novel hybrid materials opens up innovative possibilities for cutting-edge applications across numerous fields. Here, we have synthesized novel surface functionalized photoluminescent carbon quantum dots (CQDs) doped with a rare-earth element (Tb³⁺) for white light emitting diodes. High quantum yield CQDs were produced utilizing Plumeria leaves as a precursor using a one-step hydrothermal approach, and further, its optical characterization was thoroughly investigated. Herein, the functionalized CQDs demonstrate excitation-independent electroluminescence performance. The UV-LED chip and functionalized CQD were combined to create a device that emits cold white light with Commission Internationale de L'Eclairage coordinates of (0.33, 0.34), a corresponding correlated color temperature of 4995 K and color rendering index of 84.2.

A promising 1D Cd-based hybrid perovskite-type for white-light emission with high-color-rendering index

A one dimensional (1D) perovskite-type (C6H7NBr)3[CdBr5] (abbreviated 4-BAPC) was synthesized by slow evaporation at room temperature (RT). 4-BAPC crystalizes in the monoclinic system with the space group P21/c. The 1D inorganic chains are formed by corner sharing CdBr6 octahedra. Thermal measurement shows that 4-BAPC is stable up to 190 °C. Optical characterization demonstrates that the grown crystal is an indirect bandgap material with a bandgap value of 3.93 eV, which is consistent with theoretical calculations. The electronic structure, calculated using density functional theory, reveals that the valence band originates from a combination of Br-4p orbitals and Cd-4d orbitals, whereas the conduction band originates from the Cd-5s orbitals. The photoluminescence spectroscopy shows that the obtained material exhibits a broad-band white light emission with extra-high CRI of 98 under λ exc = 380 nm. This emission is mainly resulting from the self-trapped exciton recombinations within the inorganic CdBr6 octahedron, and the fluorescence within the organic conjugated ammonium salt.

Leveraging Private Enterprise: Incubation of New Industries to Address the Public Sector’s Mission-Oriented Grand Challenges

We examine how mission-oriented grand challenges—formed to address the public sector’s unmet needs through development of new technologies and products for high potential impact—originate and catalyze industry incubation. Our analysis of six prominent cases identifies the incubation process, consisting of identification of unmet needs as a grand challenge, championing and articulation of a mission, leverage of private enterprise, and success or failure of the mission for subsequent industry emergence. The resulting conceptual model highlights key similarities and differences of industry incubation stemming from the public sector’s mission-oriented grand challenges relative to industries triggered by scientific discoveries or unmet user needs where the public sector is not as salient. The analysis reveals successful outcomes are associated with the public sector’s goal setting and carrying out “market functions” pertaining to selection, coordination, and knowledge sharing. We also provide cautions and caveats regarding fault lines that may arise in public-private partnerships.

Research on Laser Illumination Based on Phosphor in Metal (PiM) by Utilizing the Boron Nitride-Coated Copper Foams

Laser-driven illumination has unique advantages in high-power applications. Taking advantage of the valuable experience of light-emitting diodes (LED) development, phosphor in silicone (PiS) is considered to be one of the most potential commercial phosphor converter solutions for laser-driven illumination. However, the thermal quenching of the PiS converter is a bottleneck problem. Herein, a boron nitride (BN)-coated copper foam strategy is introduced for the laser-driven illumination system. The phosphor/silicone is embedded in the designed BN/copper foam to form a phosphor in metal (PiM) converter. Copper foam serves as an internal connected heat transfer channel; the BN coating solves the light absorption problem of the copper foam effectively. Based on this PiM(BN/copper foam) design, the heat dissipation is effectively improved. Under high-power laser excitation (8.13 W), the PiS converter cannot reach thermal equilibrium, and therefore the temperature increases sharply up to 660 °C. In comparison, the thermal performance of an optimized PiM(BN/copper foam) converter is able to maintain excellent stability, where the maximum temperature is only 166.5 °C. The proposed PiM strategy has a maximum temperature that is 493.5 °C lower than that of the reference PiS solution. Due to the superior thermal management, the luminous efficiency of the illumination system is constantly stable at 254 lm/W, though with less phosphor mass; and the related color temperature is about 6000 K all the time. This provides a practical and feasible heat-dissipation solution for high-power laser-driven illumination.

Color inconstancy of natural teeth measured under white light-emitting diode illuminants

OBJECTIVE

To evaluate color and whiteness changes of natural teeth under nine white LED illuminants recently proposed by CIE.

METHODS

From spectral reflectance factors of 36 caries-free upper central incisors, corresponding colors under illuminant D65 and CIE 1931 standard colorimetric observer were computed for all tested illuminants, using the chromatic adaptation transform CAT16. Color differences (CIELAB and CIEDE2000 units) and whiteness (WI_D and WI_O indices) from teeth illuminated by CIE standard illuminants (D65 and A) and white LED illuminants were calculated. The appearance of 630 pairs of teeth under all illuminants was also evaluated.

RESULTS

Color gamuts from 36 teeth under tested illuminants showed similar volume and shape in CIELAB color space, but their centers of gravity changed in many different directions with respect to colors under D65 or A illuminants: Considering colors under D65/A, color shifts produced by white LED illuminants were in the ranges 2.0-8.6/1.1-7.0 CIELAB units (1.4-8.2/0.6-6.8 CIEDE2000 units). Average WI_D and WI_O values for the 36 teeth under different illuminants ranged from -5.8 to +19.3 and from -7.7 to +11.1, respectively. Considering 630 pairs of teeth, average color differences (mainly lightness differences) were below 0.5 CIELAB units (0.3 CIEDE2000 units), and average whiteness differences ranged from 8.1 to 10.7 for WI_D (23.4-25.1 for WI_O).

SIGNIFICANCE

Using CIE LED illuminants, most changes in color and whiteness for individual teeth were above typical threshold values of perceptibility and acceptability in dentistry. However, considering pairs of teeth, the average color and whiteness differences under all tested illuminants were very similar.

Building Industries by Building Knowledge: Uncertainty Reduction over Industry Milestones

Scholars have long been interested in new industry emergence, highlighting that it could often be impeded by uncertainty across four dimensions: technology, demand, ecosystem, and institutions. Building on the insight that uncertainty stems from partial knowledge, we develop a conceptual framework that utilizes a temporal and a process perspective for knowledge generation and aggregation. Industry emergence through key milestones—commercialization, firm takeoff, and sales takeoff—is made possible by knowledge-generation processes by diverse actors within and across uncertainty dimensions, and knowledge-aggregation processes with appending, selecting, and collective mechanisms at play. Our conceptual framework integrates across disciplinary perspectives to shed light on both the development of an industry poised for future growth, and the bottlenecks that may delay or even impede industries from emergence.

Improving Optical Performance of Ultraviolet Light-Emitting Diodes by Incorporating Boron Nitride Nanoparticles

Ultraviolet light-emitting diodes (UVLED) are a new type of device in the LED development; however, the radiant efficacy of UVLEDs is still too low to satisfy the requirements of applications. In this study, boron nitride nanoparticles (BN NPs) are incorporated into the UVLED’s silicone encapsulation to improve the optical output power. This BN NPs-based package shows an increase in optical flux of 8.1% compared with silicone-only encapsulation when the BN NP concentration is optimized at 0.025 wt%. By analyzing the BN NP film, adding the BN NPs into silicone leads to a decrease in transmittance but an increase in haze. Haze and transmittance has an excellent negative correlation with increasing BN concentration under 365 nm. The moderate BN NP concentration maximizes the scattering performance from haze while maintaining high transmittance. Therefore, this enhanced light output is attributed to scattering that reduces optical losses from total internal reflection at the silicone–air interface. By using the new BN-based structure in green and red quantum dot devices, an increase radiant flux of the device is observed, 9.9% for green LED and 11.4% for red LED. This indicates that BN NPs have potential prospects in the application of UV LEDs used as excitation sources for quantum dots.

Balancing technological innovation with waste burden minimization: An examination of the global lighting industry

Technological innovation has the promise to catalyze reduced environmental impacts through higher energy efficiency, product design that promotes reuse, and use of benign materials. However, as new technologies emerge, it is easy to lose sight of the environmental burden associated with technology transition and premature replacement of technology. Though product turnover can lead to gains in energy efficiency, it also can contribute to the creation of expanded and diversified waste streams. The market for residential lighting products continues to rapidly evolve, with new LED products emerging each year. Technology change in the lighting industry has unintended consequences, including new waste streams associated with the obsolete products. This paper examines the waste burden that occurs as a consequence of technology change when lighting products are replaced or upgraded. To understand the impact of residential lighting replacement, the authors used life cycle assessment to evaluate LED products. We defined three personas representing various typical technology adopters within the product adoption curve to quantify the volume and change rate of lighting products. The personas have also been used to estimate the waste impact for larger populations, and the results show that while an innovator's waste burden is lowest amongst the three personas, a non-trivial waste burden accompanies the transition to LED lighting products for all three personas. The results quantify the waste burden of high performance lighting and further motivate the development and implementation of recycling programs and policies to prevent waste diverted to landfills by consumers. The results also confirm that attention must be paid to how to reduce the waste burden of LED lighting products through improved design and lighting as a service models.

Ln3+-Induced Diblock Copolymeric Aggregates for Fully Flexible Tunable White-Light Materials

In this research contribution, nano-aggregates have been fabricated by introducing lanthanide (Ln³⁺) ions into solutions of amphiphilic diblock copolymers of polystyrene-b-poly (acrylic acid) (PS-b-PAA). The coordination of acrylic acid segments to lanthanide cations induces diblock copolymer (BCPs) self-assembly in order to design stable white luminescent hybrid nanoparticles with fine uniform particle size. The introduction of Ln³⁺ ions (Eu³⁺ and Tb³⁺) bestows the micelles, precisely white light, upon excitation of 342 nm. Lanthanide coordination cross-linking of poly (acrylic acid) segments, or blocks, endows the micelles higher thermal stability than that of BCPs micelles without cross-linking. As the most important key point of this work, the regular and stable nano-particles with high emission quality can make fully flexible electroluminescent devices with self-formation or uncoordinated into polymer hosts. Instead of inorganic luminescent nanoparticles with hard cores, this method can potentially apply for fully flexible white-light emitting diodes (FFWLEDs).

Combining near-field hyperspectral imaging and far-field spectral-angular distribution to develop mid-field white LED optical models with spatial color deviation

The integration of spatial distribution of light intensity and color in the midfield is instrumental for LED optical design. On the basis of this rationale, we proposed an accurate and convenient method for developing white LED optical models. Near-field hyperspectral images and far-field spectral-angular distributions were integrated to illustrate changes in spatial light intensity and color distribution in the mid-field, to the exclusion of the absorption, conversion, and scattering of phosphors. The corresponding optical models were developed for three LED samples under different packaging conditions. Their normalized cross-correlation values for spatial light intensity and correlated-color-temperature distribution between simulation and measurement averaged as high as 0.995 and 0.99 respectively, which validated the accuracy and feasibility of the proposed method.