The synthetic µ-diamonds powder was synthesized using high pressure high temperature technique. The metal-catalyst effect was used to reduce the pressure and temperature of diamonds synthesis. The irradiation of diamonds by focused beam of 975 nm laser diode lead to obtain intense broadband white emission with maximum at 620 nm. This type of white emission generation were described earlier for graphene ceramic and graphene foam. The emission of μ-diamonds is characterized by low threshold of power excitation and strong dependence of ambient pressure. It was suggested that the white light emission observed from graphene samples may originate from the laser-induced sp<sup>2</sup>↔sp<sup>3</sup> hybridization change as a result of the mechanism analogous to the intervalence charge transfer in Sr<sub>2</sub>CeO<sub>4</sub> nanocrystals. Similar sp<sup>2</sup>↔sp<sup>3</sup> hybridization change can occur in µ-diamonds resulting in intense, bright white light emission.
To emphasize the scientific and technological interest in the silica-based glassy systems and the versatility of the sol-gel route, nano and micrometer scale structures are discussed focusing the attention mainly on the rare-earth-activated materials and their spectroscopic characterization. We have demonstrated that various SiO<sub>2</sub>-based binary systems can be successfully employed for the fabrication of amorphous planar waveguides, glass–ceramic waveguides, and tapered rib waveguide laser. Different technological processes allowed to realize Er<sup>3+</sup> -activated microspheres that can be exploited as microresonator and it has been evidenced that through specific coating it is possible to modify modal free spectral range and/or modal dispersion of the microresonator and achieve laser action. In the case of rare-earth-doped 3-D colloidal crystals in different configurations (direct and inverse one), it has been shown that the relaxation dynamics of the electronic states can be engineered.