Crystal growth and optical characteristics of beryllium-free polyphosphate, KLa(PO(3))(4), a possible deep-ultraviolet nonlinear optical crystal

Deep-ultraviolet nonlinear optical crystals are of great importance as key materials in generating coherent light with wavelength below 200 nm through cascaded frequency conversion of solid-state lasers. However, the solely usable crystal in practice, KBe(2)BO(3)F(2) (KBBF), is still commercially unavailable because of the high toxicity of beryllium-containing and the extreme difficulty of crystal growth. Here, we report the crystal growth and characteristics of an beryllium-free polyphosphate, KLa(PO(3))(4). Centimeter-sized single crystals have been easily obtained by the flux method and slow-cooling technique. The second-harmonic generation efficiency of KLa(PO(3))(4) powder is 0.7 times that of KH(2)PO(4); moreover, the KLa(PO(3))(4) crystal is phase-matchable. Remarkably, the KLa(PO(3))(4) crystal exhibits an absorption edge of 162 nm, which is the shortest among phase-matchable phosphates so far. These attributes make KLa(PO(3))(4) a possible deep-ultraviolet nonlinear optical crystal. An analysis of the dipole moments of the polyhedra and theoretical calculations by density functional theory were made to elucidate the structure-properties relationships of KLa(PO(3))(4).