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

Novel materials doped with trivalent lanthanides and transition metal ions showing near-infrared to visible photon upconversion

Photon avalanche upconversion in rare earth laser materials

Publisher Summary The intensities of intraconfigurational f–f transitions are reviewed in the chapter The chapter presents the transition mechanisms for lanthanide ions—namely, the magnetic dipole transition, the induced electric dipole transition, and the electric quadrupole transition It discusses the way experimental intensities can be determined from the spectra The chapter also focuses on the expression of the dipole strength and the oscillator strength in oriented and in randomly-oriented systems Correction factors for lanthanide ions in a dielectric medium are described in the chapter Although only a few magnetic dipole transitions exist for the trivalent lanthanide ions, magnetic dipole transitions are of interest, because their intensities are in a first approximation independent of the ligand environment and can, thus, be used as intensity standards The intensity of a magnetic dipole transition can be calculated exactly, provided that suitable wavefunctions are available These wavefunctions can be obtained from diagonalization of the energy matrix

Chapter 167 Spectral intensities of f-f transitions

Several technical revolutions over the last ten years have led to the increasing use of rare earth-doped fiber lasers and amplifiers as a key component of optical communication systems. In this chapter, we review the methods of producing these fibers and the effect of the host composition and the rare earth doping on the quality of the final product. We then review the physics of the dopants and the hosts involved which makes these doped fibers so valuable for optical communications. In the last section, the laser performance itself is summarized; new trends for the future are presented.

Rare Earth-Doped Fiber Lasers and Amplifiers

Fluoride crystals and high lying excited states of rare earth ions

The first observation of optical properties of new rare-earth-doped vitreous fluoride waveguides has been recently reported. These vitreous fluoride films have been deposited by a physical vapour deposition technique on fluoride substrates. Several PZG films and sandwiches deposited on various substrates have been prepared with thickness of a few μm and doped in the guiding layer by various amounts of erbium and other rare-earth ions. High δn/n (10−2) has been achieved as a result of the glass compositions. Infrared as well as green and blue upconversion pumped fluorescences have been recorded under side light injection.

M.F. Joubert

Papers

Fluoride crystals and high lying excited states of rare earth ions

Infrared to visible conversion in rare-earth-doped planar waveguides

A spectroscopic study of bay2f8 : nd3+

Room temperature blue upconverted luminescence via photon avalanche pumping in Cs2NaGdCl6:Tm3+

Spectral and dynamic study of the broad band UV 4f25d→4f3 emission in Nd-doped double sodium yttrium fluoride crystals and comparison with Nd:LiYF4