Growth, Enhanced Electrical Properties, and Induced Photoluminescence of Ho-Doped Pb(Mg1/3Nb2/3)O 3 –PbTiO 3 Single Crystal

Ho-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 (Ho-doped PMN–PT) single crystal with a size of φ25 × 25 mm was successfully grown by the Bridgman technique. The 110-oriented crystal taken from the starting part of the crystal ingot was studied in detail. The Rietveld refinement and room-temperature domain configuration reveal the coexistence of monoclinic (Mc) and tetragonal (T) phases in the studied crystal. Upon heating, the unpoled crystal undergoes a Mc→T→C phase transition process, while the poled crystal undergoes a Mc→O→T→C phase transition process. The dielectric coefficient (ε33/ε0), piezoelectric constant (d33), and electromechanical coupling factor (kt) are 5725, 1450 pC/N, and 0.5, respectively, all of which are higher than those of the 110-oriented PMN–PT single crystal. The coercive field (Ec) is 5.1 kV/cm, approximately twice that of the PMN–PT single crystal. Excellent ε33/ε0, d33, and kt are attributed to the denser polar nanoregions induced by Ho doping, which is supported by the relaxor behavior and the dielectric-temperature curve at low temperatures. The increase in Ec is attributed to the coexistence of the Mc and T phases. In addition, Ho doping induces PMN–PT crystals to achieve green light emission under 454 nm excitation. The strongest emission peak is at 552 nm, and extremely high color purity is exhibited. These characteristics make the developed single crystals a promising candidate for optoelectronic intelligent devices.