Low-temperature liquid-phase epitaxy and optical waveguiding of rare-earth-ion-doped KY(WO₄)₂ thin layers

Crystalline $KY(WO_{4})_{2}$ thin layers doped with different rare-earth ions were grown on b-oriented, undoped $KY(WO_{4})_{2}$ substrates by liquid-phase epitaxy employing a low-temperature flux. The ternary chloride mixture of NaCl, KCl, and CsCl with a melting point of 480°C was used as a solvent. X-ray diffraction, differential-interference contrast microscopy, and profilometry confirmed that the layers were oriented in [0 1 0] direction with a thickness of 5–10 μm. $Tb^{3+}$, $Dy^{3+}$, or $Yb^{3+}$ ions were incorporated into the $KY(WO_{4})_{2}$ host, and their distribution coefficients were estimated by electron-probe microanalysis. The layers were crack-free and solvent inclusions could not be found, although the presence of secondary phases in the solution has been observed. The high optical quality of the layers was confirmed by the demonstration of passive and active planar waveguiding.