Electroluminescent (EL)devices are constructed using multilayer organic thin films. The basic structure consists of a hole‐transport layer and a luminescent layer. The hole‐transport layer is an amorphous diamine film in which the only mobile carrier is the hole. The luminescent layer consists of a host material, 8‐hydroxyquinoline aluminum (Alq), which predominantly transports electrons. High radiance has been achieved at an operating voltage of less than 10 V. By doping the Alq layer with highly fluorescent molecules, the EL efficiency has been improved by about a factor of 2 in comparison with the undoped cell. Representative dopants are coumarins and DCMs. The ELquantum efficiency of the doped system is about 2.5%, photon/electron. The EL colors can be readily tuned from the blue‐green to orange‐red by a suitable choice of dopants as well as by changing the concentration of the dopant. In the doped system the electron‐hole recombination and emission zones can be confined to about 50 A near the hole‐transport interface. In the undoped Alq, the EL emission zone is considerably larger due to excitondiffusion. The multilayerdopedEL structure offers a simple means for the direct determination of excitondiffusion length.

Electroluminescence of doped organic thin films

Handbook of optics

This paper reviews the theory and applications of photoacoustic (also called optoacoustic) methods belonging to the more general area of photothermal measurement techniques. The theory covers excitation of gaseous or condensed samples with modulated continuous light beams or pulsed light beams. The applications of photoacoustic methods include spectroscopy, monitoring deexcitation processes, probing physical properties of materials, and generating mechanical motions. Several other related photothermal methods, as well as particle-acoustics and wave-acoustics methods are also described. This review complements an earlier and narrower review [Rev. Mod. Phys. 53, 517 (1981)] that is mainly concerned with sensitive detection by pulsed photoacoustic spectroscopy in condensed matter.

Applications of photoacoustic sensing techniques

Energy of the first 4f7→4f65d transition of Eu2+ in inorganic compounds

Molecular Semiconductors in Organic Photovoltaic Cells

Singlet exciton energy transfer in organic solids

Energy transfer in europium doped yttrium vanadate crystals

Details of the optical-spectroscopic properties of alexandrite (${\mathrm{BeAl}}_{2}$${\mathrm{O}}_{4}$:${\mathrm{Cr}}^{3+}$) crystals were studied by different laser-spectroscopy techniques. The temperature dependences of the fluorescence lifetimes and widths of the zero-phonon lines were found to be quite different for ${\mathrm{Cr}}^{3+}$ ions in the mirror and inversion crystal-field sites. The results indicate that direct phonon-absorption processes dominate both thermal line broadening and lifetime quenching for ions in the mirror sites while phonon-scattering processes dominate the line broadening of inversion-site ions and leave their lifetime independent of temperature. Tunable-dye-laser site-selection methods were used to obtain the excitation spectra of the ${\mathrm{Cr}}^{3+}$ ions in inversion sites at low temperature and to identify six types of exchange-coupled pairs of ${\mathrm{Cr}}^{3+}$ ions in the lattice. Time-resolved site-selection spectroscopy was used to monitor the energy transfer between ${\mathrm{Cr}}^{3+}$ ions in mirror and inversion sites at both low and high temperature. Finally, high-power, picosecond pulse excitation was used to produce two-photon absorption, and the resulting emission spectrum was found to exhibit a new fluorescence band in the 400-nm spectral region.

Spectroscopic properties of alexandrite crystals.

Stimulated Raman scattering of picosecond pulses in barium nitrate crystals

Laser-excited, time-resolved site-selection spectroscopy techniques were used to investigate energy transfer between ${\mathrm{Nd}}^{3+}$ ions in ${\mathrm{Y}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$ and ${\mathrm{Y}}_{3}$${\mathrm{Ga}}_{5}$${\mathrm{O}}_{12}$ crystals. The results are consistent with a multistep diffusion type of energy transfer with the mechanisms for diffusion and trapping both involving resonant two-phonon-assisted processes.

Richard C. Powell

Papers

Singlet exciton energy transfer in organic solids

Energy transfer in europium doped yttrium vanadate crystals

Spectroscopic properties of alexandrite crystals.

Stimulated Raman scattering of picosecond pulses in barium nitrate crystals

Energy transfer among Nd 3 + ions in garnet crystals