Growth by the induced nucleated floating crystal (INFC) method and spectroscopic properties of KY1-xNdx(WO4)(2) laser materials

Double molybdates and tungstates of alkaline yttrium or gadolinium element belonging to the monoclinic structure are beginning to appear like very promising laser materials. They can be easily doped by IR laser rare-earth ions such as neodymium, ytterbium or erbium and, in addition, it is also possible to take benefit of the nonlinear properties of the host in so-called Raman shifter solid-state laser crystals. Unfortunately, it is difficult to grow high quality single crystals by using the usual pulling methods. The INFC method, previously used for the growth of KNbO3 crystals, is also suitable for pure or doped tungstates/molybdates. We report in this work the first experiments on pure or Nd3+-doped KY(WO4)(2). Contrary to classical growth methods (Kyropoulos, Czochralski, floating zone), no crystal seed supply is used: by continuous growth from a nucleus, created by controlled local transient supersaturation on the melt surface, large enough (13 x 13 x 5 mm), high optical quality crystals are made in one day (growth rate: 0.5 mm/h). During the early stage of growth, the Crystals float freely. When they become too heavy, they must be kept up by a pumping device to avoid sinking. Floating crystals are unstrained because mechanical stresses and internal thermal gradients are lowered in the growing solid. No inclusions and striations are observed owing to solvent rejection and dope feeding promoted by the thermal convection on the liquid. Melt composition was 63 mol% of K2WO4 and 37 mol% of KY1-xNdx(Wo(4))(2), x varying from 0-5 at%. The growth temperature, measured by a pyrometer, controlled by a PID 818P Eurotherm controller, was 925 degrees C during the growth time. The optical properties have been studied. The first data obtained on the infrared emission from F-4(3/2) to I-4(9/2,11/2,13/2) under similar to 800 nm excitation, that is to say a laser-diode pump one, will be given. Life-time and branching ratio measurements at room-temperature will be also added. Site-selection laser spectroscopy at low temperature has been performed in order to probe the multicenter existence of Nd3+ ions. (C) 1997 Elsevier Science B.V.