Optical Properties Of Various Strontium Bismuthates: Luminescence And Uv-Induced Photocoloration

The low-temperature photoluminescence (T<300 K) and UV-induced formation of color centers of recently synthesized Sr2Bi2O5, Sr3Bi2O6 and Sr6Bi2O11 bismuthates are examined. The estimated Mott-Seitz activation energies, ranging from 88 to 167 meV, correspond to various emission bands. Comparison of the response of all three bismuthates when exposed to UV-illumination indicates that photoluminescence and formation of color centers are two processes that compete with photocatalytic activity. The most photoactive Sr6Bi2O11 bismuthate exhibits neither luminescence nor the ability toward photocoloration. By contrast, Sr2Bi2O5, which exhibits no photocatalytic activity, displays an intense photoluminescence; UV irradiation causes significant changes of its color. The bismuthate Sr3Bi2O6 occupies an intermediate position as it exhibits some photocatalytic activity, as well as the ability to photoluminesce and to undergo photocoloration. Simple models are described to systematize the experimental results, which place these bismuthates into a new class of photoactive materials.