[Cooperative luminescence in Yb:YAG crystals]

Cooperative luminescence phenomenon of Yb:YAG crystals was studied. Up-converted blue luminescence was obviously observed in Yb:YAG under excitation in the near-infrared region with a wavelength 940 nm. Experimental evidence was provided by the fact that the intensity of 498 nm luminescence shows a quadratic dependence on excitation power, and the intensity of blue luminescence increased with the increase in Yb ion concentration. It is concluded that this luminescence is due to a cooperative process resulting from a strong interaction of Yb ions. The cooperative luminescence is possiblely assigned to the strong interaction of 4f(13) electrons and neighboring Yb3+ ions in a covalent host lattice such as YAG. Theoretical cooperative luminescence spectrum was calculated.