Biochemically active sol-gel glasses: The trapping of enzymes ☆

Singlet exciton energy transfer in organic solids

Coumarins, as a family of molecules, exhibit a wide range of fluorescence emission properties. In many cases, this fluorescence is extremely sensitive to the local environment of the molecule, especially the local polarity and microviscosity. In addition, coumarins show a wide range of size, shape, and hydrophobicity. These properties make them especially useful as fluorescent probes of heterogeneous environments, such as supramolecular host cavities, micelles, polymers and solids. This article will review the use of coumarins to probe such heterogeneous systems using fluorescence spectroscopy.

https://www.mdpi.com/1420-3049/14/1/210/pdf

The use of coumarins as environmentally-sensitive fluorescent probes of heterogeneous inclusion systems

Highly emissive (with an external quantum yield exceeding 35 percent at a 365-nanometer excitation wavelength) broadband phosphors can be synthesized from a tetraalkoxysilane sol-gel precursor and a variety of organic carboxylic acids. The air-stable phosphors were synthesized at low temperatures (less than 300°C) and displayed broad visible photoluminescence spectra that appeared white to the eye. Water-soluble phosphors can be prepared by the substitution of 3-aminopropyltriethoxysilane for tetraalkoxysilane in the synthesis. These materials are the most efficient extrinsic phosphors that do not contain activator metal ions.

https://science.sciencemag.org/content/sci/276/5320/1826.full.pdf

White Phosphors from a Silicate-Carboxylate Sol-Gel Precursor That Lack Metal Activator Ions

The main purpose of this article is to review our understanding of the predominant mechanism for defect creation in alkali halides i.e. the evolution of Frenkel (F-H) pairs from self-trapped excitons. Consideration is first given to other models of defect formation since they may play a secondary role in alkali halides and major roles in other solids. Recent experimental work is surveyed with emphasis on studies of non-radiative transitions from highly-excited self-trapped excitons, of F-centre formation and of the photochemical processes associated with impurities and with the surfaces of alkali halides. Brief descriptions are given of the photochemical process in silver halides and of recombination-induced defect migration in compound semiconductors. Finally a critical assessment is made of our understanding of the dominant mechanisms for defect formation in alkali halides with particular attention paid to the identification of the precursor state, the excited state of the self-trapped exciton ...

Creation of lattice defects by electronic excitation in alkali halides

A resonance luminescence line and its LO phonon side bands due to n =2 free excitons in KI are studied. Main results of measurements; (1) the resonance luminescence line is located at 6.186 eV which corresponds closely to the peak position of the zero phonon absorplion line due to n =2 excitons, (2) the shape of the line is symmetric Lorentzian with 1.6 meV width, (3) the quantum yield is 1 ×10 -5 , (4) the height of the potential barrier between the n =2 free exciton state and self-trapped exciton states is 3.0 meV, (5) the self-trapping probability by a tunnel process through the potential barrier is 2 ×10 11 sec -1 and (6) the scattering probability from the n =2 free exciton state to the n =1 free exciton state is 2 ×10 11 sec -1 . Furthermore, it is concluded that so called σ(4.12 eV) luminescence and π(3.31 eV) luminescence are emitted from the self-trapped exciton states due to the n =2 exciton state.

Luminescence Lines Due to the n=2 Free Exciton State of Wannier Series in KI Crystals

Time-resolved fluorescence spectra of naphthalene doped in amorphous silica glasses

Luminescence of dyes doped in a sol–gel coating film

Fluorescence decay times of naphthalene crystals were observed pulsively and their temperature dependence was analyzed with a mechanism of violated forbidden transition by molecular vibration. Fluorescence decay times of anthracene and naphthacene doped crystals were also observed by a pulsive method and the probabilities of energy transfer from singlet excitons to doped acceptors were observed. The probabilities of energy transfer were analyzed with a model that diffusing excitons transfer their energy to acceptors by dipole-dipole interactions. From the temperature dependence of the probabilities the diffusion coefficient D of an exciton was determined as 1/D=1/α'T -1/2 +1/βT 1/2 exp(hν/kT)-1, where ν is the frequency of the longitudinal optical phonon. This result means that the transport effective mass of exciton is constant in the exciton band of a naphthalene crystal. Above 250 K, the temperature dependence of energy transfer was analyzed with a thermal activation process of the excited acceptor by ...

Kenji Uchida

Papers

Luminescence Lines Due to the n=2 Free Exciton State of Wannier Series in KI Crystals

Time-resolved fluorescence spectra of naphthalene doped in amorphous silica glasses

Luminescence of dyes doped in a sol–gel coating film

Lifetimes and Diffusion of Singlet Excitons in Naphthalene Crystals

Luminescence associated with the molecular aggregation of hydrocarbons doped in amorphous silica glasses