Luminescent Properties of Phosphonate Ester-Supported Neodymium(III) Nitrate and Chloride Complexes.

This study examines the synthesis of two geminal bisphosphonate ester-supported Ln 3+ complexes [Ln( L3 ) 2 (NO 3 ) 3 ] (Ln = Nd 3+ ( 5 ), La 3+ ( 6 )) and optical properties of the neodymium(III) complex. These results are compared to known mono-phosphonate ester-based Nd 3+ complexes [Nd( L1 / L2 ) 3 X 3 ] n (X = NO 3 - , n = 1; Cl - , n = 2) ( 1 - 4 ). The optical properties of Nd 3+ compounds are determined by micro-photoluminescence (µ-PL) spectroscopy which reveals three characteristic metal-centered emission bands in the NIR region related to transitions from 4 F 3/2 excited state. Additionally, two emission bands from 4 F 5/2 , 2 H 9/2 → 4 I J (J = 11/2, 13/2) transitions were observed. PL spectroscopy of equimolar complex solutions in dry dichloromethane (DCM) revealed remarkably higher emission intensity of the mono-phosphonate ester-based complexes in comparison to their bisphosphonate ester congener. The temperature-dependent PL measurements enable assignment of the emission lines of the 4 F 3/2 → 4 I 9/2 transition. Furthermore, low-temperature polarization-dependent measurements of the transitions from R 1 and R 2 Stark sublevel of 4 F 3/2 state to the 4 I 9/2 state for crystals of [Nd( L3 ) 2 (NO 3 ) 3 ] ( 5 ) are discussed.