Effect of Co co-doping on the optical properties of ZnTe:Mn nanocrystals

Abstract

We study the effect of Co co-doping on the optical properties of Mn-doped ZnTe nanocrystals (NCs) embedded in a glass matrix. Optical absorption (OA) and crystal field theory strongly indicated the substitutional incorporation of Co ions into these semiconducting NCs as well as the characteristic transitions of these ions in the visible and near infrared spectral region. Transmission electron microscopy (TEM) images revealed an invariant NC lattice parameter with the incorporation of Mn and Co ions. The same was confirmed by X-ray diffraction (XRD). The photoluminescence (PL) spectra showed that the characteristic emission bands of Co ions (E and E) are intense and evident at low temperatures. Indeed, Raman spectra showed that the dependence of luminescence intensity on temperature is due to the electron-phonon interaction that arises from multiphonon relaxation processes. The redshifts in the PL spectra from green to orange with the incorporation of Mn ions into ZnTe NCs, and in the near infrared with increasing Co-concentration, result from sp-d exchange interactions associated with the increase in Mn and Co ions in tetrahedral sites of ZnTe NCs, which may be very interesting for applications in luminescent devices. These observations provide strong evidence that higher Co-concentrations inhibit the incorporation of Mn into ZnTe NCs, suggesting that there may be competition between Co and Mn ions substituting Zn ions and, furthermore, that these ions replace zinc vacancies (V) in these NCs.

Diluted Magnetic Semiconductors Nanocrystals: Saturation and Modulation

“…Some possible applications require nanoparticles to be embedded in highly stable, robust, and transparent host materials, as glassy systems [26]. The present study reports on the investigation of the solubility/saturation of Mn 2+ ions in Zn 1-x Mn x Te [13,26,27] and competition between Co 2+ and Mn 2+ ions into Zn 0.99-x Mn 0.01 Co x Te [14,28] nanosized DMS embedded in a glassy system with a wider Mn/Co concentration range (x = 0.000-0.800). According to the literature, the Mn 2+ /Co 2+ ion can be thermodynamically incorporated into II-VI semiconductors up to its solubility limit [29,30].…”

“…The emission centered at approximately 2.03 eV and 1.89 eV corresponds to tetrahedrally (Td) and octahedrally (Oh) coordinated Mn 2+ ions. Already, when the spin-allowed transitions centred around 1.69 eV ( 4 T 1 ( 4 P) → 4 A 2 ( 4 F), named E 1Co2+ ) and 1.52 eV ( 4 T 1 ( 4 P) → 4 T 2 ( 4 F), named E 2Co2+ ) [14]. The energy diagram in Figure 3(d)shows these OA and PL spectra transitions.…”

“…The AO spectra, besides the bands attributed to Zn 1-xMn x Te QDs and bulk NCs, as previously presented in Figure 3, four characteristic bands in the visible spectrum for all doped samples with cobalt. These four are due to the spin-allowed transitions: 4 A 2 (F) → 2 T 1 (P) (2.13 eV); and spin-forbidden transitions: 4 A 2 (F) → 2 A 1 (G) (2.33 eV), 4 A 2 (F) → 4 T 1 (G) (1.95 eV) and 4 A 2 (F) → 2 E(G) (1.91 eV) [14]. These bands show the substitutional incorporation of Co 2+ ions in tetrahedral Zn 2+ ions sites.…”

“…These bands show the substitutional incorporation of Co 2+ ions in tetrahedral Zn 2+ ions sites. The PL spectra show emissions from two NC groups: QDs (E exc ~ 2.53 eV) and bulk NCs (E b ~ 2.21 eV); defects related to zinc vacancies (E VZn ~ 2.53 eV) and oxygen centers (E o ~ 1.91 eV) [14,27].…”

“…In this context, we investigated the doping saturation limit in nanopowders of DMS Zn 1-x Mn x O NCs [12] and Zn 1-x Mn x Te [13], Zn 0.99-x Mn 0.01 Co x Te [14], and Bi 2-x Co x S [15] NCs synthesized in glassy matrices by the fusion method. The properties of the nanomaterials were investigated by experimental techniques of photoluminescence (PL), UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (MET).…”