Ultraviolet and blue emission from crystalline SiO2 coated with LiNbO3 and LiTaO3

Crystalline SiO2 (alpha quartz) coated with LiNbO3 (LN) or LiTaO3 (LT) films emits two strengthened luminescence bands at 368 and 468 nm compared with those of pure alpha-SiO2, when excited with 280 nm light of a Xe lamp. These two bands strongly depend on the coating: the LN-coated alpha-SiO2 has a much stronger photoluminescence (PL) than the LT-coated alpha-SiO2. On the other hand, the two bands are different from those of alpha-SiO2 in that their excitation spectra do not have any noticeable band in the range 200-320 nm. They could be understood based on excitons in the alpha-SiO2 surface, which are induced by the photorefractive effect of the coated films. The 368 nm PL band is attributed to the optical transitions of the E' defect pairs and the 468 nm PL band to the radiative recombination of the self-trapped excitons. (C) 1999 American Institute of Physics. [S0003-6951(99)01813-6].