OPTICAL ABSORPTION OF Y3AL5O12 FROM 10-CM TO 55000-CM-1 WAVE NUMBERS

The optical absorption coefficient of synthetic single crystals of the garnet Y3Al5O12 has been measured from photon wave numbers of 10 to 55 000 cm-1 at 300°K. The wave-number range 10 to 900 cm-1 has been studied at 4°K. The 17 theoretically predicted absorption peaks of the Y3Al5O12 lattice at 300°K have been found at wave numbers of 123, 163, 223, 255, 293, 332, 373, 395, 430, 457, 510, 530, 570, 690, 722, 784, and 830 cm-1. The fourteenth, fifteenth, and sixteenth peaks are believed to be associated with the ν̄3 vibrations of the AlO4 groups in the lattice. The multiphonon lattice absorption bands extend upward to 2400 cm-1 wave numbers. Beyond 2400 cm-1 the crystal is transparent, with an absorption coefficient <0.1 cm-1 up to ν̄=30000 cm-1. From 30 000 to 52 000 cm-1 the absorption appears to be dominated by trace impurities. The optical absorption increases rapidly for wave numbers above 52 000 cm-1 and reaches an absorption coefficient of 10+3 cm-1 at 54 300 cm-1 wave numbers (6.73 eV or 1840 ). Some comments are also made on the relationship of the lattice modes of yttrium aluminum garnet (YAG) to the phonon sidebands of electronic transitions of impurity ions in YAG. © 1969 The American Physical Society.