Spectral absorption of tellurium in alkali borate glasses

The spectral absorption of tellurium-containing lithium, sodium and potassium borate glasses in the range of 300–700 nm was used to identify the states of tellurium formed in such glasses. Depending on the nature and concentration of the alkali oxide the glasses obtained were either colourless, rose which is attributed to the formation of the polytelluride ion or grey which is attributed to the formation of elemental tellurium particles. The tellurites and/or tellurates are expected to form in glasses of high content of either Na₂O or K₂O which were colourless. The sequence of formation of the different states of tellurium with increasing alkali content is in accordance with acidity-basicity concept.