Effect of magnetic ordering on the photoluminescence of EuS and EuTe

Giant tunability of exciton photoluminescence emission in antiferromagnetic EuTe

“…This behavior indicates that the broad band A is caused by self-activated emission associated with deep centers, as observed also in other wide-gap semiconductors, 14,15 whereas the lines in band B clearly correspond to excitonic transitions. This assignment is in contrast to all previous work on EuTe, [9][10][11] where the excitonic emission lines were not observed. Figure 3 shows PL spectra of the annealed sample within the region of the excitonic emission lines as a function of excitation power I e .…”

“…These 4 f levels are located in between the conduction and the valence band, where the latter is formed by the p orbitals of the chalcogenes. While all previous optical studies of EuTe performed on powders, 9 polycrystalline thin layers, 10 or bulk crystals 9,11 showed only a very broad luminescence at transition energies around 1.5 eV, we find that high-purity epitaxial EuTe layers grown by molecularbeam epitaxy exhibit very narrow excitonic photoluminescence ͑PL͒ lines at about 1.9 eV that have not been observed in previous studies. These excitonic lines exhibit a giant magnetic-field tunability by more than 240 meV for magnetic fields between 0 and 7.2 T, with an essentially constant tuning slope of 34 meV/T.…”

Hysteresis loops of the energy band gap and effective g factor up to 18 000 for metamagnetic EuSe epilayers

“…The samples were grown by ultrahigh vacuum molecular-beam epitaxy on lattice-matched BaF 2 substrates and therefore exhibit a very high purity and an excellent crystalline quality, in contrast to the samples used in previous studies. 6,[11][12][13] From our optical studies, we observed abrupt steplike changes in the band gap energy as a function of the applied external magnetic field as well as clear hysteresis loops when the magnetic field sweep direction is reversed. From the comparison with superconducting quantum interference device (SQUID) magnetization measurements these effects are shown to be caused by the magnetic phase transitions in EuSe at certain critical field values, and it is demonstrated that the magnitude of the redshift of the energy band gap is directly proportional to the sample magnetization.…”

Dicroísmo circular magnético no espectro de absorção em calcógenos de európio

“…Este extenso raio determina sua fraca energia de ligação (0, 01 eV ) (8) (14) como vimos em (1.1.1). Para descrever seus resultados, em particular a evolução térmica da luminescência, Busch et al (12) utilizaram o modelo do pólaron magnético. Porém, a forte variação dos espectros em função do campo magnético aplicado, e o deslocamento de Stokes, indicam uma excitação mais complexa, sendo necessário a utilização de um modelo de coordenada conguracional com fator de Huang-Rhys muito grande conforme Akimoto et al (13).…”