Raman scattering experiments have been carried out to study persistent densification in SiO(2) glass following hydrostatic compression at room temperature. A new relationship linking selective Raman parameters to the degree of densification in the glass has been developed here. This approach will allow quantification of the residual densification in silica following microindentation experiments, with the goal being the development of a constitutive law for amorphous silica.

The elastic and plastic behaviors of silica glasses densified at various maximum pressure reached (12 GPa, 15 GPa, 19 GPa, and 22 GPa), were analyzed using in situ Raman and Brillouin spectroscopies. The elastic anomaly was observed to progressively vanish up to a maximum pressure reached of 12 GPa, beyond which it is completely suppressed. Above the elastic anomaly the mechanical behavior of silica glass, as derived from Brillouin measurements, is interpreted in terms of pressure induced transformation of low density amorphous silica into high density amorphous silica.

Density changes of GeO 2 and SiO 2 glasses subjected to irradiation by tightly focused femtosecond pulses are observed by Raman scattering. It is shown that densification caused by the void formation in GeO 2 glass is very similar to the changes under hydrostatic pressure. In contrast, the experimental observations in SiO 2 glass could be explained by pressure effect or by the fictive temperature anomaly, i. e., a resultant smaller specific volume of the glass (a denser phase) at a high thermal quenching rate. Density changes of GeO 2 and SiO 2 glasses are opposite upon close-to-equilibrium heating; this gives new insights into the mechanisms of densification under highly non-equilibrium conditions: fs-laser induced micro-explosions, heating and void formation. The pressure and temperature effects of glass modification by ultra-short laser pulses are discussed considering applications in optical memory, waveguiding, and formation of micro-optical elements.

The in situ elastic and plastic behaviors of sodium aluminosilicate glasses with different degrees of depolymerization were analyzed using Brillouin spectroscopy. The observed elastic anomaly progressively vanished with depolymerization. The densification process appears to be different from that observed in pure silica glass. In the plastic regime of densified glasses hysteresis loops were observed and related to modification of the local silicon environment facilitated by the addition of sodium.

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N-doped homo-epitaxial GaN samples grown on freestanding GaN substrates have been investigated by micro-Raman spectroscopy. Quantitative analysis of the E2h and the A1(LO) modes’ behavior has been performed while intentionally increasing the carrier density using silicon doping. We noticed that as the carrier concentration increases up to 1.8 × 1018 cm−3, the E2h mode remains unchanged. On the other hand, when the doping gets higher, the A1(LO) position shifts to a higher frequency range, its width becomes larger, and its intensity drastically diminishes. This change in the A1(LO) behavior is due to its interaction and its coupling with the free negative charge carriers. Furthermore, we calibrated the A1(LO) frequency position shift as a function of the n-carrier concentration. We found out that for low n doping, the change in the A1(LO) position can be considered as a linear variation while in the overall doping range, a sigmoid growth trend with a Boltzmann fit can be tentatively applied to describe the A1(LO) position shift. This calibration curve can also be used to describe the coupling strength between the carriers and the A1(LO) phonon. Eventually, this study shows that micro-Raman spectroscopy is a powerful non-destructive tool to probe the doping concentration and the crystalline quality of GaN material with a microscopic spatial resolution.

Five Tb3+/Eu3+ mixed nonanuclear clusters with the general formula [Eu9–xTbx(acac)16(µ3‐OH)8(µ4‐O)(µ4‐OH)] ([Eu9–xTbx], x = 0.9–8.1, acac = acetylacetonate) were synthesized. Characterization by powder X‐ray diffraction (PXRD), energy‐dispersive X‐ray spectroscopy (EDS) and inductively coupled plasma optical emission spectroscopy (ICP‐OES) highlight a near‐perfect match between the amounts of Tb3+ and Eu3+ ions input in the reaction mixture and the amounts in the clusters. The luminescence properties of these [Eu9–xTbx] clusters were investigated thoroughly in the solid state, and a strong energy transfer from the Tb3+ to Eu3+ emitters was evidenced. Thus, these nano‐nonanuclear 4f clusters, which can be viewed as square pyramids that share one top, exhibit dual luminescence that can be adjusted by controlling the ratio of the lanthanide ions within the crystal architecture.

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