Relations among nonbridging oxygen, optical properties, optical basicity, and color center formation in CaO–MgO aluminosilicate glasses

Abstract

In this study the relations among nonbridging oxygen ͑NBO͒, optical properties, optical basicity, and color center formation in CaO-MgO aluminosilicate glasses were studied. Samples containing ͑in mol %͒ 35.9-57.5 of CaO, 16-27.7 of Al 2 O 3 , 7.9-41.6 of SiO 2 , and 6.5-6.9 of MgO were measured by optical absorption and excitation, luminescence, and Raman spectroscopy. The results showed that when the SiO 2 content was increased, the absorption edge shifted toward lower wavelengths and the bonds between O 2− ions and cations became more covalent. These observations were confirmed by Raman results that showed a decrease in the number of NBO per silicon tetrahedron as a function of SiO 2 content. The results indicate that the effects of higher NBO concentration are the narrowing of the band gap energy and the delocalization of O 2− electrons, which facilitates the O 2− electrons to be trapped by anion vacancies and, consequently, forming color centers. The relationship between color center formation and SiO 2 content was confirmed by optical spectroscopic measurements under UV radiation.

Tunable light emission and similarities with garnet structure of Ce-doped LSCAS glass for white-light devices

“…Our low-silica-content glass is located in the small glassy region, region (2), which is surrounded by a non-glass phase. This difference between CAS and LSCAS glasses leads to different optical and structural properties that can be observed by Raman spectra and measurements of the optical basicity and band gap, as previously reported [31]. The observed yellow emission of Ce 3+ :LSCAS glass under violet excitation and the knowledge that this emission is only observed in materials with garnet structures led us to suppose that the LSCAS local glass structure may have similarities to the garnet structure.…”

“…Fig. 7 shows the Raman spectra in terms of the peak intensities and positions of different aluminate and silicate garnets, such as Ca 3 Al 2 (SiO 4 ) 3 (grossular) [31,33], YAG [34], TAG and DAG [35], our LSCAS glass, and other non-silicate or -aluminate garnets such as MgSiO 3 [39], YAP [40], ZrSiO 4 [41] and MgAl 2 O 3 [42]. Between 500 and 600 cm −1 , all aluminate-and silicate-garnet materials show vibration bands related to the Si, Al-O bands of tetrahedra, as previously mentioned, and bands between 700 and 950 cm −1 related to Si and Al-O stretch modes.…”

“…Because LSCAS and CAS glasses do not present any well defined Raman bands below 400 cm −1 , just a continuum non-zero signal shoulder, we will focus our discussion mainly on the region related to internal vibrations. Some examples of silicate garnets like grossular (Ca 3 Al 2 (SiO 4 ) 3 ) [31,33], uvarovite (Ca 3 Cr 2 (SiO 4 ) 3 ) [31,33] and aluminate garnets such as YAG [36] and TAG [37] present internal vibrations that can be divided in three main spectral regions: 450-550 cm −1 , 690-800 cm −1 and 800-910 cm −1 . These intervals are related to the internal vibrations of AlO 4 and SiO 4 tetrahedra present in the structure with similar energies.…”

Magnetic Properties of Synthetic Gehlenite Glass Microspheres

“…Magnetic properties of the amorphous gehlenite glass prepared in flame synthesis, especially the presence of χ T N , signal the existence of a non-bridging oxygen and oxygen vacancies (larger ring structures), taken into account local composition fluctuations, and perhaps even the trapped electrons or the electron anions [4][5][6].…”

Synthesis and luminescent properties of Eu3+/Eu2+ co-doped calcium aluminosilicate glass–ceramics

“…) was prepared after melting the mixture under vacuum at 1600 1C for 2 h. The details about glass preparation are described elsewhere [19]. The as-prepared glass was cut into desired dimensions and polished before crystallization and subsequent characterizations.…”