No abstract

The well‐ordered array of pores and walls made up of nanocrystallites in a mesoporous titania thin film can be doped with high concentrations of Eu3+ (up to 8 mol %) to create a bright red photoluminescent material (see picture). The photoluminescence arises from energy transfer through excitation of the titania nanocrystallites in their band gap to the crystal field states of the europium ions; photoluminescence concentration quenching is prevented because of the high surface area and nanocrystalline structure of the material.

Quantum dot (QD) resonators for microcavity lasing applications were successfully synthesized by a single system diblock copolypeptide mediated process. Using specifically tailored block peptides and nanoparticles, we present here the cooperative assembly of cadmium selenide (CdSe) QDs and silica nanoparticles into 3-dimensional microcavities with a high QD volume fraction. These hollow QD microspheres are a perfect combination of both quantum and optical confinement, in which the electronic states of the 3-dimensional confined semiconductor nanocrystals are coupled to the photonic states of the spherical microcavity. We show that the specific interaction between the mode properties of the cavity with the emission of its QD building blocks leads to room-temperature microcavity lasing without the use of additional mirrors, substrate spheres, or gratings.

As long as product molecules of 2 are not yet aligned in their own crystal lattice, hut in the rebuilt lattice of 1, short-wavelength excitation can cause a photochemical reverse reaction. Only crystalline 2 photodimerizes exclusively to form the cyclobutane derivative [9].The lack of absorption of light at 2. = 365 nm by the crystalline product 2 prevents the formation of its [2 +2]-dimer. Irradiation of 1 (4 h) with light from a 150 W Hanau Hg high-pressure lamp passed through a Wertheimer UVW-55 bandpass filter (isolation of the 365nm light with 2.8% contribution from 334 nm light ( % transmission <1 at 315 nm and at 410 nm)) in a powder cuvette leads to a considerable shift of the diffuse reflectance spectrum to curve bin Figure I. whereas the broad-band irradiation (>. > 300 nm) ofcrystalline 2 produces a decrease in the long-wavelength absorption and an increase in a band of the photodimer 191 at 266 nm.