Istar

Time-resolved luminescence spectra were acquired using a nanosecond-pulsed Nd:YAG laser-pumped OPO (Vibrant B, Opotek Inc.) as an excitation source at 394 nm (0.4–1.0 mJ). Dried solid powders were placed in quartz cells (1 mm × 10 mm) and tilted by ∼30° to the incident excitation laser beam path. Emissions were collected using a fiber bundle connected to a spectrograph (SR-303i, Andor Technology). An intensified CCD (ICCD) (iStar, Andor Technology) was used as the detector and its insertion delay time was managed relative to the incident laser pulse.^{26 (link)} A long-path filter (500 nm cutoff) was placed in front of the detector to protect it from the scattered excitation light. The ICCD was set with a gate width of 5 ms and a gain of 1. Spectra were collected by accumulating luminescence signals from 100 excitation bursts. A grating of 600 lines per mm was mainly employed with a slit width of 10 μm.
Luminescence lifetimes, the inverse of the decay rate (τ = 1/k_obs), were measured using the kinetic mode of the ICCD with a series of delayed gate openings from the burst of the incident laser pulses. The inner-sphere hydration number (N(H₂O)) of the Eu(iii) ion was calculated based on its established relationship with the luminescence lifetime (τ), as expressed in eqn (1).^{27,28 (link)}