Lasers and Excited States of Rare Earths

Tuning the Decay Time of Lanthanide‐Based Near Infrared Luminescence from Micro‐ to Milliseconds through d→f Energy Transfer in Discrete Heterobimetallic Complexes

“…The concomitant determination of the Ru-centered quantum yields F Ru overcomes this limitation, and confirms the existence of intramolecular Ru!Ln energy transfers at 295 K (see Table S12 in the Supporting Information). (9,10).…”

“…(2)] when Nd III is used as an acceptor because its 4 F J (J = 3/2, 5/2, 7/2, 9/2), 2 H J (J = 9/2, 11/2), and 4 S 3/2 excited levels are available for overlapping with the M-centered emission spectra in the 13 000-15 000 cm À1 range, while only two ( 4 F 9/2 and 4 I 9/2 ) and one level ( 2 F 5/2 ) are accessible for Ln = Er and Yb, respectively. [10] At 295 K, the thermally-activated vibrational processes explain the faster luminescence decays of the donor k M Lum , but the parallel trend observed for the energy transfer process k M,Ln ET suggests that both M-centered de-excitation processes (i.e., luminescence and energy transfer, Table 6) depend on closely related phonon-assisted mechanisms at high temperature. Consequently, the efficiency of the energy transfer processes…”

“…[8] Moreover, the lower energy of the excited states in NIR emitters is compatible with visible sensitization processes outside the range of biological absorption, thus offering perspectives for improved detection limits. [9] Lanthanide-based NIR emitters are also used for optical amplification in lasers [10] and silica-based fiber optic networks, for which the emission wavelengths (1330 nm for Pr III and 1550 nm for Er III ) match the "window of transparency" in silica used for telecommunication. [11] Potential applications are thus obvious, but designing efficient sensitization for lanthanide-based NIR emitters remains a challenge, because the Laporte-forbidden 4f!4f transitions prevent direct excitation of the photoluminescence.…”

“…[11] Potential applications are thus obvious, but designing efficient sensitization for lanthanide-based NIR emitters remains a challenge, because the Laporte-forbidden 4f!4f transitions prevent direct excitation of the photoluminescence. [10] For Pr III , Nd III , and Er III , the plethora of accessible excited levels in the 6000-35000 cm À1 range is compatible with indirect sensitization processes, during which a suitable aromatic chromoAbstract: Inert and optically active pseudo-octahedral Cr III N 6 and Ru II 6 (Ln = Nd, Eu, Yb, Lu) and [RuLnL 3 ]-(CF 3 SO 3 ) 5 (Ln = Eu, Lu) demonstrate that the helical structure can accommodate metal ions of different sizes, without sizeable change in the intermetallic M···Ln distances. These systems are ideally suited for unravelling the molecular factors affecting the intermetallic nd!4f communication.…”

“…[14] In this context, the alternative use of a d-block complex as a donor, well-separated from the lanthanide acceptor, offers the potential for a rational approach, since multipolar electrostatic interactions (with or without phonon-assistance) become the only vectors for intramolecular nd!4f energy transfer processes. [10,[12][13][14] The first systems matching this criterion took advantage of the intense charge-transfer transitions, often mixed with d-d transitions, occurring in the visible spectral range of redox-active d-block complexes, to efficiently collect photonic energy. Intersystem crossing (isc) followed by multipolar nd!4f energy transfer complete the energy funneling processes leading to the lanthanide-based NIR emission.…”