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A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 degrees C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source. The dyes that can serve as fluorescence lifetime standards for time-domain and frequency-domain measurements are all commercially available, are photostable under the conditions of the measurements, and are soluble in solvents of spectroscopic quality (methanol, cyclohexane, water). These lifetime standards are anthracene, 9-cyanoanthracene, 9,10-diphenylanthracene, N-methylcarbazole, coumarin 153, erythrosin B, N-acetyl-l-tryptophanamide, 1,4-bis(5-phenyloxazol-2-yl)benzene, 2,5-diphenyloxazole, rhodamine B, rubrene, N-(3-sulfopropyl)acridinium, and 1,4-diphenylbenzene. At 20 degrees C, the fluorescence lifetimes vary from 89 ps to 31.2 ns, depending on fluorescent dye and solvent, which is a useful range for modern pico- and nanosecond time-domain or mega- to gigahertz frequency-domain instrumentation. The decay times are independent of the excitation and emission wavelengths. Dependent on the structure of the dye and the solvent, the excitation wavelengths used range from 284 to 575 nm, the emission from 330 to 630 nm. These lifetime standards may be used to either calibrate or test the resolution of time- and frequency-domain instrumentation or as reference compounds to eliminate the color effect in photomultiplier tubes. Statistical analyses by means of two-sample charts indicate that there is no laboratory bias in the lifetime determinations. Moreover, statistical tests show that there is an excellent correlation between the lifetimes estimated by the time-domain and frequency-domain fluorometries. Comprehensive tables compiling the results for 20 (fluorescence lifetime standard/solvent) combinations are given.

The possibility of hole transfer between a photoexcited semiconductor quantum dot and a pi-conjugated polymer is discussed. The result suggests that the polymer and the quantum dot form a relatively stable complex.

We analyze the random process of fluorescence reabsorption and trapping in solid-state optical materials in general and its influence on the efficiency of optical cooling of solids by anti-Stokes fluorescence in particular. Using the absorption and fluorescence spectra of Y[b.sup.3+]:Zr[F.sub.4]-Ba[F.sub.2]-La[F.sub.3]-Al[F.sub.3]-NaF (ZBLAN) as input data, we employ a random-walk model to test analytical approximations of the fluorescence escape efficiency and cooling efficiency, including reflections at the boundary. OCIS codes: 160.4670, 350.5340, 350.5500.

Photoenhancement effect in colloidal CdSe and (CdSe)ZnS core-shell quantum dots attached to a variety of surfactant molecules in aqueous and nonaqueous environment is observed. Results show that the effect occurs in dots suspended in a variety of organic or aqueous situations.

Femtosecond transient absorption spectroscopy and time-integrated photoluminescence (PL) measurements are used to study charge carrier relaxation in colloidal InP quantum dots (QDS). The results suggest that with increasing excitation energy, there arise relaxation pathways involving surface or external energy states exhibiting reduced radiative efficiency.

Time-resolved terahertz spectroscopy (TRTS) is used to study the ultrafast photoinduced charge separation processes in varying compositions of poly(3-hexylthiophene) (P3HT) blended with the electron acceptor [6,6]-phenyl-[C.sub.61]-butyric acid methyl ester (PCBM). The results have shown that the addition of PCBM to the polymer films have not increased the production of charge carriers within the first 2 ps, however, the charge carriers in the 0.2 and 0.5 blended films survived to much longer times than those in the P3HT and 0.8 films.

Photoluminescence (PL) spectroscopy is used to investigate the kinetics of single-walled carbon nanotube (SWNT) rebundling and diameter-dependent surfactant interactions. The results have demonstrated that surfactant desorption from suspended nanotubes is rate-limiting in the rebundling process and that the PL quenching due to bonding is first-order in the concentration of luminescent nanotubes.

2,2'-Bis(4-dimethylaminophenyl)- and 2,2'-dicyclohexyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[ d ]imidazole ((N-DMBI) 2 and (Cyc-DMBI) 2 ) are quite strong reductants with effective potentials of ca. -2 V vs ferrocenium/ferrocene, yet are relatively stable to air due to the coupling of redox and bond-breaking processes. Here, we examine their use in accomplishing electron transfer-induced bond-cleavage reactions, specifically dehalogenations. The dimers reduce halides that have reduction potentials less cathodic than ca. -2 V vs ferrocenium/ferrocene, especially under UV photoexcitation (using a 365 nm LED). In the case of benzyl halides, the products are bibenzyl derivatives, whereas aryl halides are reduced to the corresponding arenes. The potentials of the halides that can be reduced in this way, quantum-chemical calculations, and steady-state and transient absorption spectroscopy suggest that UV irradiation accelerates the reactions via cleavage of the dimers to the corresponding radical monomers., (Copyright © 2023, Tang et al.)