Creation of new functions in transparent oxides utilizing nanostructures embedded in crystal and artificially encoded by laser pulses

The main objective of this review is to provide an idea to develop new functions by utilizing exotic nanostructures and electronic structures embedded in materials. First, our materials design concept is introduced in relation to electronic structures of oxides. Then optoelectronic properties, electronic structures and device applications are reviewed for (i) layered oxychalcogenides LnCuOCh (Ln = lanthanide, Ch = chalcogen) and (ii) nano-porous crystal 12CaO7⋅Al2O3 (C12A7). Sharp blue-to-UV light emission was observed in LnCuOCh originating from room-temperature stable exciton and the high stability of exciton is discussed in terms of their two-dimensional electronic structures. C12A7 has free oxygen ions clathrated in its subnanometre-sized cages, and new functions may be rendered to C12A7 by replacing the free oxygen ions with active anionic species. Quantum calculations indicate that cages trapping electrons in C12A7:e− can be regarded as quantum dots. We also introduce micro/nano-processing techniques by interfered pulses from a femtosecond laser as another approach to add new functions to transparent material. This method enables us to write three-dimensional integrated optical circuits inside transparent materials. A miniatured distributed feedback colour centre laser structure was written inside LiF solely by laser pulses and its oscillation at room temperature was demonstrated.