PHOTOREFRACTIVE BEHAVIOR OF BA[FE(CN)(5)NO]CENTER-DOT-3H(2)O IN THE RED AND NEAR-INFRARED SPECTRAL RANGE

Phase gratings can be written in acentric Ba[Fe(CN)(5)NO]. 3H(2)O sing le crystals on the basis of extremely long-living metastable electroni c states at temperatures below T=213 K after preexposure with light in the range of 350-589 nm. The modulation of the refractive index reach es values up to Delta n=5.3x10(-4) in the red and Delta n=1.6x10(-4) i n the near-infrared spectral range. Beam-coupling experiments show tha t there is no phase shift between the light interference pattern and t he resulting refractive index grating. The dynamical behavior of the d iffraction efficiency during the writing process depends on the depopu lation velocity of the metastable electronic states SI and SII and on the transfer velocity from SI into SII. The maximum efficiency of eta= 72% is reached at an exposure of Q=27 J/cm(2) with lambda=632.8 nm. Th e grating is stable against irradiation with light of wavelength lambd a=1047 nm and cannot be destroyed with an exposure of up to Q = 600 J/ cm(2). In comparison to centrosymmetric Na-2[Fe(CN)(5)NO]. 2H(2)O, whe re the refractive index cannot be modulated perpendicularly to the mir ror plane in, such a restriction does not exist in the acentric single crystal.