Aluminate glasses are interesting candidates as host matrices
for optically active rare earth dopants, with potential applications
as phosphors for HB-LED lighting. They possess a number
of advantages in comparison both to common silicate glasses
and polycrystalline aluminates. First, they are able to accommodate
higher concentrations of rare-earth dopants in comparison
to their single- or polycrystalline counterparts of identical composition,
such as yttrium- or ytterbium aluminium garnets, or
the respective rare earth aluminate perovskites. The glasses also
exhibit good mechanical properties, especially hardness, and high
chemical and thermal resistance [1,2]. Most importantly, however,
lower phonon energies are characteristic for the aluminate glasses
in comparison to common silicate glasses that reduce the nonradiation
losses due to multiphonon relaxation and non-radiative
transitions, with resulting higher emission intensities [3]. They are
also transparent in an ultraviolet range of spectra [4], which is
of particular importance for LED phosphors excited by UV light.
Recently, up-conversion (UC) phosphors, which can up-convertthe
near-infrared (NIR) light to visible light have attracted significant
attention for their potential application in display monitors, optical
data storage, medical diagnostics, solid-state visible lighting