Optical and magnetic properties of Cr-doped ZnS nanocrystallites

Abstract

Cr-doped ZnS (molar Cr:(Cr + Zn) between 0.51% and 19.69%) nanocrystallites have been prepared through co-precipitation method. The x-ray diffraction, transmission electron microscopy, and selected area electron diffraction results show that all the samples are in sphalerite structure with average particle size about 3 nm. No impurity phase relating to Cr element is found in all the samples. X-ray photoelectron spectroscopy spectra reveal that Cr was incorporated into ZnS lattice as Cr3+. It can be seen in the UV-visible absorption spectra that, besides the intrinsic band-gap absorption of ZnS below 370 nm, there are another two absorption bands (at 425 nm and 595 nm, respectively) in the visible light range, which are the characteristic bands of Cr3+. Photoluminescence spectroscopy was also used to characterize corresponding luminescence properties of the nanocrystallites. The band-edge emission in photoluminescence spectroscopy exhibits blue-shift as the concentration of Cr increases, and several emission peaks concerned with surface states and zinc vacancies were found in the wavelength range of 400 nm ∼ 500 nm. It is confirmed that Cr doping will bring about a considerable amount of zinc vacancies. Magnetic measurements indicated that all the samples are paramagnetic and the calculated effective magnetic moments μeff of Cr3+ were close to the theoretical value of 3.87 μB. Accordingly, it seems that zinc vacancies give no contribution to the overall magnetic response of the samples.

Antiferromagnetic coupling in Co-doped ZnS

“…There have been many reports on roomtemperature ferromagnetism for wide bandgap semiconductor doped with a few percent of 3d transition-metal ions. The host materials for the DMS have been ZnO [1,[4][5][6], ZnS [2,[7][8][9][10][11][12], TiO 2 [13,14], SnO 2 [15,16], GaAs [17], AlN [18], and GaN [19]. TM-doped DMS materials always suffer from problems such as formation of secondary phase and/or clusters [2].…”

Improved magnetism in Cr doped ZnS nanoparticles with nitrogen co-doping synthesized using chemical co-precipitation technique

“…ZnS doped with transition metal ions, exhibit ferromagnetic behavior at room temperature [6] such as Mn [7], Co [8], Cu [9], Fe [10] and Ni [11]. However, ZnS doped with Cr has been investigated mainly for optical properties [12][13][14][15], but reports on magnetism in Cr doped ZnS nanoparticles are also available [16][17][18][19][20]. Zeng et al [17] observed paramagnetism in Cr-doped ZnS nanocrystallites.…”

“…However, ZnS doped with Cr has been investigated mainly for optical properties [12][13][14][15], but reports on magnetism in Cr doped ZnS nanoparticles are also available [16][17][18][19][20]. Zeng et al [17] observed paramagnetism in Cr-doped ZnS nanocrystallites. Reddy et al [18] observed room-temperature ferromagnetism in EDTA capped Cr-doped ZnS nanoparticles.…”

Pulsed laser ablation and deposition of ZnS:Cr

“…Cr-doped ZnS (ZnS:Cr) is an interesting material that potentially can be used for various spintronic [1,2] and optoelectronic applications [3]. In particular, ZnS:Cr is proposed as an intermediate band (IB) material by ab initio calculations [4] for use in intermediate band solar cells (IBSCs) [5].…”