Borosilicate optical glasses

Figure 14.3 Effect of silica content on the hardness of borosilicate optical glass. The ratio of B203 to K20 is 0.54 in these glasses. The data are from Schmidt and Reichardt...

Ultrathin porous glass membranes with variable texture properties were prepared from a Si02-rich sodium borosilicate initial glass by careful fine timing of the conditions of heat treatment for phase-separation. Pore sizes between < 1 and 120 nm can be realized. The membranes are characterized by a narrow pore size distribution. The transport, optical and mechanical properties vary with the pore size. The tailorable texture and transport characteris-... 

FIG. 119. Change in refractive index with wavelength for optical glasses (f — dense flint, 2 — light flint, 3 — borosilicate glass) (from Kingery, 1960). 

Figure 5. Uncracked and cracked Knoop indentations in the BK 7 borosilicate crown glass at 19.6 N. Indentations should be spaced further apart for most testing purposes in order to avoid interference, (a) is a bright field and (b) dark field optical microscope illumination. The dark field photo reveals that some localized cracking occurs under the left indentations, but the extent of cracking is dramatically different. The cracked indentation is 7 pjn longer.

Fig. 11. Index of refraction vs dispersion and optical classification of glasses. The shaded area indicates the region of glass formation. BaF = barium flint BaK = barium crown BaLF = light barium flint BaSF = heavy barium flint BK = borosilicate crown F = flint FK = fluorcrown K = crown ...

Let us now consider MMCT for the case in which the donating ion is a lanthanide ion with a partly filled 4/ shell M(/")M(d°)CT. The trivalent lanthanide ions with a low fourth ionization potential are Ce, Pr ", Tb ". Their optical absorption spectra show usually allowed 4f-5d transitions in the ultraviolet part of the spectrum [6, 35]. These are considered as MC transitions, although they will undoubtedly have a certain CT character due to the higher admixture of ligand orbitals into the d orbitals. In combination with M(d°) ions these M(/") ions show MMCT transitions. An early example has been given by Paul [36] for Ce(III)-Ti(IV) MMCT in borosilicate glasses. The absorption maximum was at about 30000 cm ... 

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