Room-temperature photochemical hole burning of Eu3+in sodium borate glasses

Persistent spectral hole burning (PSHB) has been observed at 77 K to room temperature for Eu 3+ in sodium borate glasses with compositions of x Na 2 O·(100-x)B 2 O 3 ( x = 10,25,35). Glasses melted in air do not show the phenomenon of PSHB, while room-temperature PSHB occurs in the glasses prepared by melting in reducing conditions. 151 Eu Mössbauer spectra reveal that europium ions are present as both Eu 3+ and Eu 2+ in glasses melted in reducing conditions. The relative hole area increases with an increase in the molar ratio of Eu 2+ to Eu 3+ when the content of Eu 2+ is low, whereas the relative hole is almost independent of the molar fraction of Eu 2+ when the content of Eu 2+ is high. Furthermore, a comparison of hole burning among sodium borate glasses with the molar fraction of Eu 2+ being almost the same as one another shows that the hole area grows larger as the content of Na 2 O becomes higher. These observations are interpreted in terms of the photoinduced redistribution of electric charges between Eu 3+ and Eu 2+ . The effect of the glass composition on hole widths is also discussed based on the structural change in sodium borate glasses.