Phosphate glasses with low dispersion and relatively high refractive indices (compared with sil-
icate-based optical glasses) were developed for
achromatic optical elements about 100 yr ago by
Schott and co-workers. Subsequent interest in al-
kaline earth phosphate glasses stemmed from their
high transparency for ultraviolet (UV) light, again
when compared with silicate glasses. However, the
poor chemical durability of these early optical
glasses limited their applications and (temporarily)
discouraged their further development. (See [1] for
a description of these early studies and citations to
them.)
In the 1950s, interest in amorphous alkali
phosphates was stimulated by their use in a variety
of industrial applications, including sequestering
agents for hard water treatments and dispersants
for clay processing and pigment manufacturing [2].
By studying such materials, Van Wazer [2] estab-
lished the foundations for much of our present
understanding of the nature of phosphate glasses.
About the same time, Kordes and co-workers [3,4]
re-examined the alkaline earth phosphate glasses,
including UV-transmitting compositions, and
noted some ÔanomalousÕ trends in properties which
they suggested showed a compositional-depen-
dence for the coordination number of metal ca-
tions like Zn2.
The advent of solid state lasers in the 1960s
heralded a new era of phosphate glass research.
Certain compositions have large rare-earth stim-
ulated emission cross-sections and low thermo-
optical coecients (compared with silicate glasses)
and are the materials of choice, particularly for
high power laser applications [5]. (Campbell and
Suratwala review the development of Nd-doped
phosphate laser glasses elsewhere in this volume
[6].)
Morees to borosilicate glass for immobilization of radioactive waste.[2]