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The short-wavelength sub-nanosecond luminescence in BaF 2 material, discovered in the early 80s, gave a new direction to research into fast scintillators and phosphors. In contrast to 'typical' luminescence occurring within the forbidden band gap, the new type of emission was due to transitions between the upper core and valence bands. Thus it was named core-valence luminescence (CVL); the terms cross-luminescence and Auger-free luminescence have also been used. Given its unusual nature, this new luminescence process has attracted considerable interest in the field of condensed matter physics. During the sequent decades (till the end of the previous century) CVL has been experimentally observed in several dozen compounds and the conditions for detecting CVL have been established. Interest in this kind of luminescence increased in recent years due to the emergence of new methods of crystal synthesis, the development of high-speed solid-state photodetectors, and the construction of unique modern set-ups using synchrotron radiation. This paper analyzes the numerous studies of CVL, obtained mainly over the past decade. Experimental and theoretical data on this topic are considered in detail. Special attention is given to new results on scintillation characteristics of BaF 2 in the form of single crystals, ceramics, nanoparticles, and composites. The features of CVL in binary and ternary compounds are discussed. Some Cs- and Ba-based ternary halides show relatively high light yields and represent promising fast scintillators. The prospects of using materials with CVL as fast scintillators for time-of-flight positron emission tomography and other applications are deliberated. • Overview of recent theoretical and experimental findings on Core Valence luminescence. • Most attractive CVL crystals for ultrafast scintillator applications analyzed. • Prospects for future studies and underexplored CVL materials listed. [ABSTRACT FROM AUTHOR]

• Easy method to remove the cupping layer covering the topological insulator. • Using glue to remove the cupping layer. • Surface modification of MBE topological insulator. The topological categorization originates from a depiction of the sequencing of bands around the band gap of the material in comparison to the normal vacuum type band ordering. The structure can either be normal or inverted, and thus topologically trivial or non-trivial. An odd number of Dirac fermions on the surface occurs in this type of material. Time-reversal symmetry is responsible to preserve the surface bands. On the other hand, topological crystalline insulator is protected by mirror symmetry; this system has an even number of Dirac surface state per BZ. Capping layer of Te or Se is necessary due to the high sensitivity of films surfaces to atmospheric pressure. The capping layer works as a protection from oxidation. In Bi 2 Te 3 samples, the bonds between Bi and Te are covalent bonds while the bonds between Te-Te at a certain position are van der Waals bonds. Thereby, the bonds between amorphous Te cap and sample surface is weaker than van der Waals bonds within the sample structure. However, the top boost cleaving method was successful. But, for Pb 1-x Sn x Te samples the top boost cleaving method unsuccessfully results. The bonds between the metallic Pb 1-x Sn x Te sample surface and amorphous Te cap are stronger than van der Waals bonds in BaF 2 substrate, i.e. F-F van der Waals bonds. In this paper, we present different techniques to recover fresh surfaces, from classical methods (such as sputtering and annealing) working for all types of films and top boost methods, which could be less used due to the strong bonds in some films. Moreover, we were able to recover the immaculate surfaces for non-capped samples. We present here in a systematic study by low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS), and angle-resolved photoemission spectroscopy (ARPES). [ABSTRACT FROM AUTHOR]