Correlation among the cooperative luminescence, cooperative energy transferred Eu3+-emission, and near-infrared Yb3+ emission of Eu3+-doped LiYb(MoO4)2

The optical properties (down-conversion and up-conversion spectra, the luminescence decay) of LiYb1−xEux(MoO4)2 are investigated in unusually wide Eu3+-concentration range from x = 0.0 to x = 1.00. In the down-conversion spectra under 266 nm excitation, the intensity of the 2F5/2 emission of Yb3+ increases with increasing Eu3+-concentration x from 0.01 to 0.8 and then decreases with increasing x from 0.8 to 1.00. This is explained by cross-relaxation (CR) between Eu3+ and Yb3+. In the up-conversion spectra under 975 nm excitation, cooperative luminescence (CL) due to Yb-pair is observed, together with up-conversion red Eu3+ and Yb3+ emissions. The CL intensity decreases quickly as x increases from 0 to 0.05, decreases gradually up to x = 0.4, and then disappears at x > 0.4. Unlike the case of the 266 nm excitation, the Yb3+ emission abruptly decreases with increasing x from 0 to 0.10, but never disappears at x > 0.4. The up-converted red Eu3+ emission intensity increases with increasing x up to x = 0.5, then decreases to zero at x = 1.0. The concentration dependences of these CL, Yb3+, and up-converted Eu3+ emissions are understood by CR between Eu3+ and Yb3+ and by competition between radiative transition of Yb-pair and energy transfer from the excited Yb-pair to Eu3+ ions.