Different purification techniques for carbon dots.

Carbon dots (CDs) are zero-dimensional quasi-spherical nanoparticles endowed with excellent advantages including good luminescence features, photostability, low cytotoxicity, remarkable aqueous solubility, favourable biocompatibility, low risk to environment and great flexibility in surface modification. Fluorescent CDs that can selectively respond to specific inorganic/organic target molecules in environmental and biological samples are of prime significance amongst the new generation intelligent sensors due to the critical involvement of different ions/molecular species in not only human health, but also in environment processes. In this context, preparation of CDs from bioprecursors has immense significance due to the involvement of green principles, inexpensive, clean, nontoxic, easily accessible, renewable and large-scale production can be realized. This article aims at exploring different types of green raw materials including plant biomass, animal products, food items and waste materials as carbon sources for the synthesis of both undoped and doped CDs. The emphasis is given on different synthetic approaches adopted for improving the quantum yield without any chemical modification, the characterization techniques, mechanistic origin of photoluminescence and fluorescence response mechanisms involved in the sensing action towards various analytes. The significant benefits and limitations of CDs obtained from eco-friendly precursors through green approaches are summarized. Various challenges and the future prospects of these carbonaceous nanomaterials as sensors are also discussed. Graphical

Organic light-emitting devices (OLEDs) have garnered significant research attention owing to their immense application prospects in leading technologies for full-color flat panel displays and eco-friendly solid-state lighting. They demonstrate exceptional features such as mercury-free construction, wide viewing angle, superior color quality and captivating flexibility. The requirements of light-emitting organic materials pertaining to high stability, lifetime and luminescence quantum yield, combined with the fabrication of devices with high performance efficiency, are highly challenging. Rational molecular design of 1,8-naphthalimide (NI) derivatives can offer quite promising results in achieving standard-light-emitting materials with a wide range of colors for OLED applications. This review is mainly focused on the synthesis and usage of varyingly substituted NI frameworks as luminescent host, dopant, hole-blocking and electron-transporting materials for OLEDs that emit not only red, orange, green and blue colors, but also function as white emitters, which can really have an impact on reducing the energy consumption. The future prospects that could be explored to improve the research in the highly promising field of OLEDs are also discussed. Graphical abstract

Optoelectronics is an active area of research and, for few decades, development of different semiconducting materials with a wide emission window has attracted researchers. Organic light emitting diodes (OLEDs) are primarily utilized in displays and light sources that greatly contribute towards the conservation of energy and do not need a backlight for displays. Development in device efficiency, lifetime and stability is now a major concern in this particular application, and designing efficient material for OLEDs has been an active field of research for decades. Metal-organic compounds possess different optical and electronic properties due to metal and organic ligand interactions which are primarily used in OLEDs. This review is mainly focused on the Schiff bases and their metal chelates as a pure emitting layer or as a dopant material for the fabrication of R/G/B/white emitting devices. Moreover, future prospects to explore further to advance research in the OLED arena are also discussed. Graphic Abstract