It has been an outstanding problem that a semiconducting host in the bulk form can be doped to a large extent, while the same host in the nanocrystal form is found to resist any appreciable level of doping rather stubbornly, this problem being more acute in the wurtzite form compared to the zinc blende one. In contrast, our results based on the lattice parameter tuning in a Zn(x)Cd(1-x)S alloy nanocrystal system achieves approximately 7.5% Mn(2+) doping in a wurtzite nanocrystal, such a concentration being substantially higher compared to earlier reports even for nanocrystal hosts with the "favorable" zinc-blende structure. These results prove a consequence of local strains due to a size mismatch between the dopant and the host that can be avoided by optimizing the composition of the alloyed host. Additionally, the present approach opens up a new route to dope such nanocrystals to a macroscopic extent as required for many applications. Photophysical studies show that the quantum efficiency per Mn(2+) ion decreases exponentially with the average number of Mn(2+) ions per nanocrystal; en route, a high quantum efficiency of approximately 25% is achieved for a range of compositions.

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Efficient hydrogen (H 2 ) production from renewable energy source is the most important requirement to produce clean fuels. Developing materials systems with high activity and good stability for solar energy conversion has become one of the most prominent and challenging research fields in the interdisciplinary scientific community. Recently, metal-free and graphite-like carbon nitiride (g-C 3 N 4 ) based on tri-s-triazine (heptazine) units has received much attention in the photocatalysis research due to its low cost, good stability and excellent optical and electronic properties.

Bi3+ and Sb3+ doping (and codoping with lanthanides) in Cs2SnCl6 vacancy ordered perovskites and Cs2MInCl6 (M = Na, K, Ag) double perovskites has been shown to open up new opportunities for solid state lighting. Bi3+ and Sb3+ with ns2 outer electronic configuration can tailor both optical absorption and emission properties for phosphor-converted light emitting diode (pc-LEDs) applications. Therefore, the s-electron dopants (Bi3+ and Sb3+) act as both sensitizers and emitters. This is because the dopant s-electrons contribute near the band edges of the host, unlike the cases of d- and f-electron dopants. Consequently, Bi3+ doping can also act as a sensitizer for lanthanide luminescence in systems like Bi3+-Ln3+ codoped Cs2AgInCl6, where Ln = Er, Yb, Tb. In this perspective, we provide insights on the tailoring of electronic and optical properties by ns2 electron doping. These insights are then connected to the rational design of hosts, dopants, and codopants, for their potential applications. Finally, we discuss challenges and opportunities for future research.