D. Pacheco

Luminescence characteristics of BaMnF4 and KMnF3

Abstract The observed spectral behavior of the luminescence of BaMnF4 and KMnF3 is found to be consistent with the emission from three localized traps which are situated below the excitonic level of the Mn2+ ion.

Fluorescence studies of the Er ↔ Ho and Er ↔ Tm energy transfer in erbium aluminum garnet

Abstract We have studied the flourescence characteristics of Ho 3+ and Tm 3+ in ErAlG:Ho, Tm and investigated the Er ↔ Ho and Er ↔ Tm energy transfer present in this system. In the infrared, the crystal ErAlG:Ho, Tm presents three groups of sharp lines (centered at ∼18 000, ∼19 300, and ∼21 000 A), whose intensities are strongly temperature-dependent. The first two groups are attributable to the Tm 3 H 4 → 3 H 6 transition, while the third group represents the Ho 5 I 7 → 5 I 8 transition. In YAlG:Er (50%), Ho(2%), only the Ho emission centered at ∼21 000 A is observed in the infrared. Under pulsed excitation, the emissions at ∼17 900, ∼19 000, and ∼21 000 A in ErAlG:Ho, Tm present a double exponential decay; the time dependences of the decays of the first two emissions are essentially the same; however, the 19 000 and 21 000 A emissions present different decay patterns. In YAlG:Er (50%), Ho (2%), on the other hand, the decay of the 21 000 A emission is purely exponential at all temperatures studied. The above results for ErAlG:Ho, Tm are explained by means of a rate-equation model in which the Ho → Er and Tm → Er transfer are treated as activation-type processes which effect a coupling between (1) the Ho and Tm ions, and (2) the Ho or Tm ions and quenching impurities.

The impurity-induced luminescence of RbMnF3

Abstract The impurity-induced luminescence of RbMnF 3 has been studied in the temperature range, 4–120 K. Multimagnon sidebands of impurity-induced Mn 2+ emission lines have been detected spanning the spectral range, 5515–5960 A. The broad emission bands, which peak at 5750 A and 6440 A, have been attributed to phonon-assisted transitions from two impurity-induced Mn 2+ traps of different depths. Pulsed luminescence measurements indicate that the quenching of the shallow trap emission is by a thermal activation to the E1 exciton level whereas the quenching of the deeper trap emission is by a multiple phonon decay. The coupling between Mn 2+ ions is strong enough to support a detectable transfer of excitation between these two traps. The results of this research also include the observation in absorption of the E1 exciton line and its 1-magnon and possible 2-magnon sidebands.

Fluorescence Studies of Concentrated Mn2+ Systems

This article presents a review of some of the basic optical properties of concentrated Mn2+ systems and includes some recent experimental observations on the system KMnF3. The first three sections describe the general features of the well-known systems MnF2 and RbMnF3. The emphasis is on the spectral and thermal characteristics of the broad bands seen in emission in the 5800–7000 A res ion. These sections serve as an introduction to the fourth and last section, which deals with our current studies of the crystal KMnF3. This last system is of interest because it presents absorption and excitation properties which are very similar to those of MnF2 and RbMnF3 and yet displays emission properties which are rather different from those of the other systems. Finally, a phenomenological model is given to explain the observations.

Generalized Excitations in Pure Ionic Crystals

The basic formalism underlying the theory of generalized excitations in crystals is presented. The starting point is the phenomenon of quantum-mechanical resonance, in which two degenerate levels, upon being coupled, equally share the excitation energy of the system. With this example as a prototype, the basic properties of a generalized excitation in a quantum-mechanical system are discussed. The general theory is applied to three special cases: optical phonons, Frenkel excitons and magnons. The interactions among these different types of excitations are also presented and discussed.

Nonradiative energy transfer without quenching of donor lifetime in Mn-based crystals

Abstract Examples and models of energy transfer from Mn 2+ to dopants or energy sinks in Mn-based crystals without quenching of the Mn 2+ lifetime are presented.