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.