Cr‐related energy levels and mechanism of Cr²⁺ ion photorecharge in ZnS:Cr

Abstract

It is shown that published data and interpretation concerning the energy and origin of Cr‐related defects in ZnS:Cr as well as the mechanism of the Cr2+ → Cr+ photorecharge are ambiguous and contradictory. New data concerning these questions obtained by means of photodepolarization (PDP) spectroscopy methods for the first time are given. Several peaks of the impurity photocurrent are revealed in the PDP spectrum of ZnS:Cr thin‐film structures, which was measured from 0.7 eV to 3.9 eV. Two peaks are due to the photoionization of Cr2+ and Cr+ ions (2.8–3 eV and 1.3–1.5 eV, respectively). Three peaks are attributed to Cr‐related lattice defects, namely, a $ [{\rm Cr}^{2+}_{\rm Zn}]^0 $ isovalent trap (∼3.5 eV) and a $ [{\rm Cr}^{+}_{\rm Zn}]^- $ acceptor isolated (∼2.7 eV) and associated with a donor (1.8–2.2 eV). A new interpretation of the mechanism of the photorecharge of Cr2+ ions is also proposed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Progress in Cr2+and Fe2+doped mid‐IR laser materials

“…15 electroluminescence in the Cr:ZnS(Se) thin-film structure under AC excitation (ACTFEL). The strong increase of the Cr 2+ emission intensity proportional to Q 6 was reported in [102], where Q is the charge transferred through the EL film for the applied voltage cycle.…”

Mid‐infrared luminesce of ZnS:Cr2+‐glass composite and fiber

“…It can be observed that the ZnS:Cr 2+ materials obtained by different methods both show interesting flat and broadband luminescence in the waveband of 1700‐2900 nm with the FWHM of ~690 nm under the excitation of a 1480 nm laser diode. The Mid‐IR emission can be attributed to the typical transition of tetrahedrally coordinated Cr 2+ : 5 E → 5 T 2 . It is noteworthy to note that the emission intensity of samples obtained by hydrothermal process (purple line) and high‐temperature solid‐phase reaction method (green line) is different: the intensity of the green line has a sharp rise compared with the purple one.…”

“…The Mid-IR emission can be attributed to the typical transition of tetrahedrally coordinated Cr 2+ : 5 E → 5 T 2 . [24][25][26] It is noteworthy to note that the emission intensity of samples obtained by hydrothermal process (purple line) and high-temperature solid-phase reaction method (green line) is different: the intensity of the green line has a sharp rise compared with the purple one. In our experiment, H 2 O and organic solvents were used in hydrothermal synthesis process.…”

Laser oscillation in Cr2+ :ZnS waveguide thin-film structures under electrical pumping with impact excitation mechanism

“…The lower symmetry results in a longwavelength shift of the band. Cr 2+ ions with the lowest local symmetry are predominant obviously in highly doped Cr:ZnS films because of increasing the number of charged defects, in particular of [Cr Zn + ] − acceptors [16].…”