Spin Selection Rules in Radiative and Nonradiative Recombination Processes in Bulk Crystals and in Thin Films of II-VI Compounds

Abstract

The origin of a fast component of Mn 2+ intra-shell photoluminescence (PL) decay is discussed. We demonstrate that efficient spin-dependent interactions between localised spins of Mn ions and spins of free carriers result in a variation of formation and decay rates of PL emissions in diluted magnetic semiconductors and affect spin selection rules for radiative recombination transitions.Introduction The influence of spin selection rules on rates of radiative and nonradiative recombination transitions is discussed, based on the results of photoluminescence (PL), PL kinetics, optically detected magnetic (ODMR) and cyclotron (ODCR) resonance investigations of ZnMnS, ZnCdSe and CdMnTe crystals, quantum well (QW) and quantum dot (QD) structures. First, the influence of spin-dependent processes on efficiency and on PL dynamics of the Mn 2+ 4 T 1 ! 6 A 1 intra-shell transition in ZnMnS (thin films and bulk samples) and in CdMnTe (bulk, QW and QD samples) is analyzed. Then, we discuss the mechanisms of the ODMR detection and Auger-type nonradiative recombination of bound excitons. Finally, we evidence influence of disorder and of magnetic interactions on rates of exciton formation and recombination in CdTe/CdMnTe and ZnCdSe/ZnSe QWs.

Dynamics of Light Emission in CdMnS Nanoparticles

“…PL, time-resolved PL, electron spin resonance (ESR), SEM, and cathodoluminescence (CL) experiments were performed. The set ups used in the present study are described elsewhere [2][3][4]. Some groups claimed that transition metal and rare earth (RE) ions do not enter nanoparticles of II-VI compounds (see the recent review by Hu and Zhang and references therein [11]).…”

“…This explains the observed drop in the PL intensity of Mn 2+ intra-shell emission with a characteristic lifetime of free carriers. We have drawn a similar conclusion from the recent investigations of ZnMnS nanoparticles and CdMnTe quantum dots [2][3][4]. Co-excitation of free carriers and excited Mn 2+ ions is necessary for observation of shortening of the Mn 2+ PL decay time [2][3][4].…”

“…Such interactions can also reduce PL decay time of the Mn 2+ intra--shell emission, by relaxing spin selection rules [2][3][4]. Based on the present PL kinetics investigations we confirm that these interactions are in fact important.…”

“…These investigations enable us to confirm an enhancement of the Mn 2+ intra-shell emission in nanoparticles. Such enhancement was reported for the first time by Bhargava and Gallagher for ZnMnS nanoparticles [1] and then was observed by us for several other systems [2][3][4].…”

Doped nanoparticles for optoelectronics applications

“…For example, the 4 T 1 to 6 A 1 intra-shell transition of Mn 2+ ions is a parity and spin (transition between spin quartet and sextet) forbidden process. Thus, this transition is fairly inefficient in bulk samples, especially in sulfides and selenides [5][6][7][8][9][10][11][12].…”