Triethylammonium picrate: An above-room-temperature phase transition material to switch quadratic nonlinear optical properties

Abstract

To switch quadratic nonlinear optical (NLO) effects has become an exciting branch of the NLO material science. However, solid-state molecular crystals showing tunable and switchable NLO behaviors remain scarce. Here, we report an organic picrate-based binary molecular crystal, triethylammonium picrate (TEAP), which undergoes an above-room-temperature phase transition at Tc=319K, being solidly confirmed by the thermal and dielectric measurements. A large thermal hysteresis of ∼7K discloses the first-order feature for its phase transition. More strikingly, the quadratic NLO effects of TEAP can be switched in the vicinity of Tc. That is, TEAP exhibits NLO-active response of ∼1.5 times as large as that of KDP below Tc (i.e., NLO-on state), while its NLO effects totally disappear above Tc (NLO-off state). Structure analyses disclose that the order-disorder transformations of triethylammonium cations and picrate anions collectively contribute to its phase transition, as well as switchable NLO behaviors. This work opens up a new pathway to the designing and assembling of stimuli-responsive materials.