Liquid Phase Epitaxy Growth of Tm³⁺ and Yb³⁺ Doped MgWO₄ Crystalline Thin-Films

Single-crystalline layers of MgWO4 doped with Tm3+ and Yb3+ were successfully grown by the liquid phase epitaxy (LPE) method on (010) oriented MgWO4 substrates using K2W2O7 as a solvent, for the first time. These layers were transparent and free of cracks, with the Tm:MgWO4 layer reaching a thickness of up to 300 μm and the Yb:MgWO4 layer up to 90 μm. Structural and morphological characterizations were performed to evaluate the quality of both types of doped layers. High-Resolution X-ray Diffraction (HRXRD) rocking curves revealed full width at half-maximum (FWHM) values of 115 arcsec for the Tm3+-doped layer and 140 arcsec for the Yb3+-doped layer, in close agreement with their respective substrates reflecting a good crystal quality and a highly ordered lattice structure. Environmental Scanning Electron Microscopy (ESEM) analysis showed well-defined and continuous interfaces for both samples, and electron probe microanalysis (EPMA) measurements confirmed that the dopants remained confined within the epitaxial regions. The lattice mismatch between the layers and the substrate was calculated and found to be very low. These results demonstrate the capability of the LPE technique to produce relatively thick and optically transparent MgWO4 epitaxial layers doped with different rare-earth ions. The interface between the substrate and the epitaxial layer was very sharp. Based on the known spectroscopic properties of Tm3+- and Yb3+-doped MgWO4 bulk crystals, these films represent promising candidates for applications in thin disk lasers with simplified pump geometry.