Room-temperature photochemical hole burning of Eu3+ in sodiumborate glasses

Abstract

Persistent spectral hole burning (PSHB) has been observed at 77 K to roomtemperature for Eu3+ in sodium borate glasses with compositions of xNa2O·(100-x)B2O3 (x = 10,25,35). Glasses meltedin air do not show the phenomenon of PSHB, while room-temperature PSHB occursin the glasses prepared by melting in reducing conditions. 151EuMössbauer spectra reveal that europium ions are present as both Eu3+and Eu2+ in glasses melted in reducing conditions. The relative hole areaincreases with an increase in the molar ratio of Eu2+ to Eu3+ whenthe content of Eu2+ is low, whereas the relative hole is almostindependent of the molar fraction of Eu2+ when the content of Eu2+is high. Furthermore, a comparison of hole burning among sodium borate glasseswith the molar fraction of Eu2+ being almost the same as one anothershows that the hole area grows larger as the content of Na2O becomeshigher. These observations are interpreted in terms of the photoinducedredistribution of electric charges between Eu3+ and Eu2+. The effectof the glass composition on hole widths is also discussed based on thestructural change in sodium borate glasses.