Oxide–based glass ceramics are promising class of solid state materials because they are using thermally stable and chemically inert glass oxide matrix that can be filled with oxide micro and nanosized crystalline particles distributed through the matrix [1–3]. The glass-ceramics are used in various optical applications for creation of new generation of optical fibers, for efficient incoherent and coherent sources of light and for the light converting materials [4–7]. Development of such efficient glass matrices suitable for creation of glass-ceramic materials for several purposes is an important practical task. In many earlier studies, one of the components of the developed glass-ceramics is a boron oxide, B2O3, because it is one of the best glass forming oxides. Diboron trioxide as a glass former is characterized by a wide glass-formation range of concentrations, high transparency, and, moreover, high thermal stability [8–10]. Borate-based glass materials possess high mechanical, chemical and thermal stability and they are widely used for the needs of optical science, related techniques and biomedical application. That is why, in our research of glass-ceramic luminescent converters for WLEDs we have focused on the borate glass matrix. Besides, the addition of some network modifiers to boron oxide, usually alkali oxides, can lead to an increase of coordination number of some of the boron atoms from 3 to 4, changing the properties of borate glass. This phenomenon, known as the “borate anomaly” can improve mechanical properties of the glass [10–12]. In the present study we use lithium oxide as the second glass former component of the developed ceramics.
The third component of the here developed glass matrices for glass-ceramic composites, vanadium pentoxide V2O5, is favorable for several reasons. Firstly, it is a glass-forming component that modifies the local structure of the borate glass network [13–15]. Secondly, V2O5 component increases light absorption of glass matrix from near UV and violet visible ranges. Noted that, in order to keep high transparency of glass and ceramics, content of the V2O5 component should be enough small and by several estimations it should not exceed 3–5% [16]. Thirdly, it is possible to use vanadate nanoparticles for creation of ceramic compositions, and presence of vanadate groups in both the glass matrix and the nanocrystalline component can significantly increase the efficiency of excitation energy transfer between glass and crystal components in ceramics and to enhance in such a way the intensity of their luminescence.
Additional advantage of new developed glass-ceramic materials could also be the ability of glass matrix to emit luminescence. Recently, borate glass compositions have been described, those are characterized by the own luminescence emission at visible light excitation [17]. There are the undoped lithium-vanadate-borate glass materials. The observed luminescence emission of the undoped lithium-vanadate-borate glass has been reported for the first time and its mechanisms are not investigated yet. At the same time, understanding of processes responsible for luminescence excitation and emission transitions is very important if the glass composition is used as matrix for creations of ceramic materials, to predict and study possible interaction of glass and crystal phases and excitation energy transfer between them. In order to investigate origin and nature of the glass matrix emission and its interaction with crystalline activators, in this paper we study spectral properties of the xLi2O-yV2O5-(100-x-y)B2O3 glass samples using additionally IR and UV-Vis spectroscopy and UV band-to-band excitation of luminescence.