Long‐Lived Photoinduced Charge Separation in (Zinc, Lead) Phosphate Glass–C₆₀ Composites

Abstract

Photoinduced charge separation and electron transfer are the fundamental phenomena involved [1±4] in the processes of light energy storage for photosynthesis in plants, xerography, photovoltaic (PV) energy conversion, etc. For the efficient photovoltaic harvesting of light energy, it is necessary, however, to have well-stabilized charge-transfer products. One impending problem in achieving a long-lived photoinduced charge transfer in an artificial system is its competing backtransfer reaction. The stability of the charge-separated state, on many occasions, is facilitated by carrier delocalization and by the spatial separation of electrons and holes, [1,3] and researchers often employ heterogeneous media [2,4] for this purpose. We report here the preparation of a group of (zinc, lead) phosphate glass±C 60 heterostructures that show a long-lived photoinduced electron transfer from the divalent lead center (Pb 2+ ) to the fullerene, upon 230±400 nm ultraviolet irradiation, which creates Pb 3+ -type hole centers and C 60 fullerene related anions in the system. Both the steady-state photoinduced absorption (PIA) and photoinduced electron spin resonance (PIESR) spectra of the irradiated system support the above view. An analysis of the carrier dynamics suggests that the electrons migrate from the hole sites to the fullerene sites in a tunneling mode. The charge-separated state thus formed in these systems has a lifetime ranging from a few hours to days, which is longer than those hitherto reported for various donor±acceptor systems. Figure 1 shows a photograph of one of the samples of the (Zn, Pb) phosphate glass±C 60 composites. Steady-state PIA spectra recorded at 300 K, in the region k = 250±1250 nm both before and after 90 min of UV-vis irradiation of the (Zn, Pb) phosphate glass±C 60 composite having a zinc oxide (ZnO) content of 40 mol-% and a fullerene (C 60 ) concentratioñ 5.0 10 ±5 M, are shown in Figure 2 (along with the absorption spectrum of a similarly irradiated base glass). Prior to irradiation, the composite exhibited a weak and broad absorption band at around 520 nm and another, less distinct, broad band around 830 nm.Considering the energy and weakness of the transition at 520 nm, one can easily recognize [5,6] it to be the highest-occupied molecular orbital to lowest-unoccupied molecular orbital (HOMO±LUMO) forbidden transition of the incorpo-COMMUNICATIONS Adv. Mater. 2003, 15, No. 3, February 5 Fig. 1. Photograph of a C 60 -doped (Zn, Pb)±phosphate glass sample.Fig. 2. Steady-state PIA spectra of a C 60 -doped (zinc, lead) phosphate glass (with ZnO = 40 mol-%; C 60 fullerene concentration = 5 10 ±5 M), along with the absorption spectrum of a similarly irradiated base glass (thickness, d = 0.2 cm, for both samples), recorded at 300 K, as a function of time. Inset: a plot of PIA intensity versus time.

Long-Lived Spin-Correlated Pairs Generated by Photolysis of Naphthalene Occluded in Non-Brønsted Acidic ZSM-5 Zeolites

“…This very long charge separation was found to be unusual with respect to the lifetime of the photoinduced charge separated state exhibited in solution and in faujasitic zeolites. The electron−hole pair generated by photolysis of NAP occluded in Li 6.6 ZSM-5 appears more stable than other long-lived photoinduced charge separation in heterogeneous media recently reported . The electron−hole pairs NAP@M n ZSM-5 •+•- stabilized in nonacidic M n ZSM-5 zeolites exhibit characteristic broad bands in the 480−530 nm region (Table ).…”

23 Fullerenes

“…A long-lived charge separation has been observed in a phosphate glass- [60]fullerene composite under 230-400 nm UV irradiation. 209 Thin films and monoliths of mesostructured silica containing embedded [60]fullerene can be prepared by a sol-gel route by either adding [60]fullerene during the synthesis or by adsorption after the synthesis is complete. 210 Silica coated fullerenols have been prepared as uniform spherical particles in which the fullerene moiety is retained as the central core.…”

Complex formation by bismuth and boron with fullerene (C60): A reaction that opens up a novel route for synthesis of C60–inorganic hybrid composites

“…In one of our earlier works we developed a stable photosensitive phosphate glass-C 60 composite. 9 However, as in the other cases, the maximum possible doping level of C 60 concentration is limited.…”

“…Fullerene C 60 has many interesting optical and optoelectronic properties, [1][2][3][4][5][6][7][8][9] and for this reason it has drawn much attention of physicists, chemists, and materials scientists. For practical application of any of its useful properties in a solid state device it is necessary to incorporate C 60 in a suitable solid host.…”