This review article provides the state-of-art research and developments of the rectenna device and its two main components – the antenna and the rectifier. Furthermore, the history, efficiency trends, and socioeconomic impact of its research are also featured.

The rectenna (RECTifying antENNA), which was first demonstrated by William C. Brown in 1964 as a receiver for microwave power transmission, is now increasingly researched as a means of harvesting solar radiation. Tapping into the growing photovoltaic market, the attraction of the rectenna concept is the potential for devices that, in theory, are not limited in efficiency by the Shockley–Queisser limit. In this review, the history and operation of this 40-year old device concept are explored in the context of power transmission and the ever increasing interest in its potential applications at terahertz frequencies, through the infrared and visible spectra. Recent modeling approaches that have predicted controversially high efficiency values at these frequencies are critically examined. It is proposed that to unlock any of the promised potential in the solar rectenna concept, there is a need for each constituent part to be improved beyond the current best performance, with the existing nanometer scale antennas, the rectification and the impedance matching solutions all falling short of the necessary efficiencies at terahertz frequencies. Advances in the fabrication, characterization, and understanding of the antenna and the rectifier are reviewed, and common solar rectenna design approaches are summarized. Finally, the socioeconomic impact of success in this field is discussed and future work is proposed.

Graphitic and amorphous C-dots share common characteristics in their photoluminescence behavior. However, the graphitic dots have a lead as electrocatalyst for fuel cells, sensitizers, and electron acceptors for solar cells.

The emergence of carbogenic nanoparticles (C-dots) as a new class of photoluminescent (PL) nanoemitters is directly related to their economical preparation, nontoxic nature, versatility, and tunability. C-dots are typically prepared by pyrolytic or oxidative treatment of suitable precursors. While the surface functionalities critically affect the dispersibility and the emission intensity of C-dots in a given environment, it is the nature of the carbogenic core that actually imparts certain intrinsic properties. Depending on the synthetic approach and the starting materials, the structure of the carbogenic core can vary from highly graphitic all the way to completely amorphous. This critical review focuses on correlating the functions of C-dots with the graphitic or amorphous nature of their carbogenic cores. The systematic classification on that basis can provide insights on the origins of their intriguing photophysical behavior and can contribute in realizing their full potential in challenging applications.

The paper argues that solar photovoltaic or wind systems would need to be implemented at a rate of hundreds of gigawatts each year to obviate the continuing worldwide growth of fossil-fueled electricity generation. It suggests that an electricity consumption tax could constitute a sustainable mechanism for funding such an endeavor.

It is observed that the atmospheric content of carbon dioxide rose by approximately 16 Gt in 2012. A non-negligible contribution to this increase must surely have come from the 35 Gt of CO2 emitted by fossil fuel consumption that year, of which 11 Gt came from fossil-fueled electricity generation (FFEG). Yet, new FFEG plants continue to be built. Although it is questionable whether economic forces would permit a halt to the construction of such plants, it is argued that, from the perspectives of technology, manufacturing capability, land availability, and cost, it could be feasible to use solar photovoltaic and wind plants to provide for the annual increase in the worldwide need for electricity. However, the required capital expenditure cost of approximately US$ 0.5 trillion per year might be difficult to raise by conventional methods for funding renewable energy plants. A number of alternative funding mechanisms are examined. Among them, an electricity consumption tax is found to be capable of providing an assured amount of regular funding on this scale. In North America and Europe, such a tax would add approximately 1 US¢/kWh to present electricity tariffs. In other regions, it would amount to an addition of 2–5 US¢/kWh.

Light-emitting diodes (LEDs) made from wide band gap semiconductors, such as gallium nitride, are undergoing rapid development. Solid-state lighting with these LEDs is transforming patterns of energy usage and lifestyle throughout the world.

With solid-state lighting gradually taking over from incandescent and fluorescent lighting, light-emitting diodes (LEDs) are very much the focus of research nowadays. This compact review takes a look at LEDs for lighting applications made from wide band gap semiconductors. A very brief history of electric lighting is included for completeness, followed by a description of blue-emitting LEDs that serve as pump sources for all ‘white’ LEDs. This is followed by a discussion on techniques to extract more light from the confines of LED chips through surface patterning. The thermal management of LEDs is perhaps the most important consideration in designing and using LED-based luminaires. This topic is discussed with regard to recent studies on LED reliability. The very promising development of gallium nitride-on-silicon LEDs is examined next followed by a discussion on phosphors for color conversion in LEDs. LED lighting has positively influenced both upscale and downscale illumination markets worldwide. Its societal impact is examined, with the review concluding with a look at efforts to produce LEDs from zinc oxide – a material that holds much promise for the future of solid-state lighting.