An excellent ultraviolet nonlinear optical crystal derived from the polar methylphosphonate unit

[C(NH 2 ) 3 ] 2 [CH 3 PO 3 ] is an UV NLO crystal with the polar [CH 3 PO 3 ] units in an ordered arrangement, exhibiting a phase-matching SHG response, suitable birefringence, a wide UV transparency window, good stability and facile crystal growth.