Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

Singlet exciton energy transfer in organic solids

Luminescence Decay by Energy Migration and Transfer: Observation of Diffusion-Limited Relaxation

A novel white-light-emitting phosphor Ca9Lu(PO4)7:Eu2+,Mn2+ has been prepared by solid-state reaction. The photoluminescence properties indicate that there is an efficient energy transfer from the Eu2+ to Mn2+ ions via a dipole−quadrupole reaction. The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Upon excitation of UV light, white light is realized by combining a broad blue-green emission band at 480 nm and a red emission band at 645 nm attributed to the Eu2+ and Mn2+ ions. The energy-transfer efficiency and critical distance were also calculated. Furthermore, the phosphors can generate lights from blue-green through white and eventually to red by properly tuning the relative ratio of the Eu2+ to Mn2+ ions through the principle of energy transfer. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for a UV white-light LED.

Ca9Lu(PO4)7:Eu2+,Mn2+: A Potential Single-Phased White-Light-Emitting Phosphor Suitable for White-Light-Emitting Diodes

Quasi-three-level solid-state lasers using trivalent rare earth ions are efficient sources in the near- and mid-infrared spectral regions. Their unique properties arise from special energy level structures in different host materials and highly efficient laser operation became possible with the availability of highly efficient high-brightness pump sources like laser diodes. This work will give an overview of quasi-three-level solid-state lasers emitting in the wavelength range 1–5 μm. Recent research and advances in spectroscopic and laser results will be presented. In comparison to four-level lasers such as e.g. Nd3+ lasers at 1.06 μm, quasi-three-level lasers show a much stronger influence of temperature on laser performance, mainly due to the thermally induced changes in the spectroscopic properties of the laser medium. Nevertheless, highly efficient lasers can be realized by direct diode pumping with high spatial and spectral brightness laser diodes. The population dynamics in the manifolds also play an important role and ion concentrations are used to minimize or maximize energy-transfer effects. These general topics will be addressed in Sect. 1, in which basic aspects of quasi-three-level lasers and their description are discussed. Section 2 deals with the general energy-level structure of trivalent rare earths in hosts, from which the most interesting ions and their transitions can be derived. These ions, Nd3+, Yb3+, Er3+, Tm3+ and Ho3+, are investigated in detail in Sect. 3 in order of their emission wavelengths, focusing on their spectral properties and laser results in different laser architectures and host media. In Sect. 4 the work is finally summarized.

Quasi-three-level solid-state lasers in the near and mid infrared based on trivalent rare earth ions

Effects of diffusion on energy transfer between molecules are considered by using two methods. One is the scattering length method, and the other is the Pade approximant with the diffusion constant as the expansion parameter. From these methods we obtain the decay function of the emission by excited molecules in a closed form of time t . The decay constant is expressed as a function of diffusion constant and is compared with the experimental results obtained by Tomura and Ishiguro.

Effects of Diffusion on Energy Transfer by Resonance

The Green's function method for the calculation of orbital energies which was discussed in a preceding paper is applied to the calculation of the lower excited states of the benzene molecule. The Dyson equation for the polarization (particle—hole) propagator is derived with the diagrammatic technique and the secular equation which gives poles of the polarization propagator is solved. The random phase approximation is not used in our calculation. Theoretical results are discussed in comparison with experimental data. Using a model system of two π-electrons, our method is compared with the equations-of-motion method.

Calculation of lower excited electronic levels of benzene with the Green's function method

Calculation of orbital energies in π-electron systems with the Green's function method. II. Application to the benzene molecule

A Green's Function Method for Calculation of Electronic States of pi-Electron Systems

Simulations on soliton dynamics in polyacetylene (PAC) systems are carried out based on an improved SSH model. The results show that the threshold for stability of soliton dynamics in PAC is not so high. We also investigate the soliton dynamics in the presence of a charged dopant. Simulations of the soliton dynamics in an external electric field show that the effective inertial mass of a soliton is very large. This is due to soliton-phonon couplings.

Osamu Tanimoto

Papers

Effects of Diffusion on Energy Transfer by Resonance

Calculation of lower excited electronic levels of benzene with the Green's function method

Calculation of orbital energies in π-electron systems with the Green's function method. II. Application to the benzene molecule

A Green's Function Method for Calculation of Electronic States of pi-Electron Systems

Simulations on soliton dynamics in polyacetylene systems