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Abstract: Calcium yttrium tetrametagermanates Y2CaGe4O12 doped with Er3+ and Er3+/Yb3+ reveal upconversion emission in visible spectral range under near-infrared excitation, λ ex =980nm. For the solid solution Er x Y2−x CaGe4O12 concentration dependencies for the green and red lines of the visible emission around 526nm (2H11/2 → 4I15/2), 545nm (4S3/2 → 4I15/2) and 670nm (4F9/2 → 4I15/2) show the optimal value for the sample x =0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y2CaGe4O12:Er3+ is discussed for an 808nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y2CaGe4O12:Er3+ and Y2CaGe4O12:Er3+, Yb3+ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ ex =1064nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition 4I13/2 → 4I15/2 in erbium ions has been detected. [ABSTRACT FROM AUTHOR]

Abstract: Luminescent properties of the new group of crystalline optical materials Ln2CaGe4O12, Ln=Dy, Ho, Er, Tm, Yb were studied under laser excitation at λ=976nm in the stationary mode. Er2CaGe4O12, Ho2CaGe4O12 and also the solid solution Ln x Y2− x CaGe4O12 (0⩽x⩽2) may be used in photonics as optical elements, such as converters and resonance amplifiers. [Copyright &y& Elsevier]