Synthesis, Optical and Structural Properties, and Charge Carrier Dynamics of Cu-Doped ZnSe Nanocrystals

Abstract

Stable and luminescent Cu-doped ZnSe nanocrystals (NCs) were synthesized in organic solvents with octadecylamine (ODA) as the capping ligand and characterized using a combination of optical and structural characterization techniques. Successful doping was achieved by adding Cu during the growth phase of the NCs when their size was ∼4 nm. The appearance of red-shifted, intense photoluminescence (PL) peak with doping indicates the incorporation of Cu in the NCs, and stability of dopant emission infers the internal doping of NCs. Extended X-ray absorption fine structure (EXAFS) studies revealed that Cu is surrounded by four neighbors in the lattice but is very close to the NC surface and gets oxidized when NCs are precipitated from the solution. For the undoped sample, time-resolved PL studies using time-correlated single photon counting (TCSPC) reveal the luminescence decay lifetimes of about 1.1, 12, and 60 ns that we attribute to near-bandedge, shallow trap (ST) state, and deep trap (DT) state emissions, respectively. In addition to these decay components, the Cu-doped sample was found to have a long-lived component with a lifetime of 630 ns. Luminescence decay lifetimes of near-bandedge and ST state emissions were slightly shortened by doping (1 and 10 ns, respectively), suggesting that the Cu dopant competes with these states in trapping the charge carriers from the conduction band (CB) or near-bandedge states. However, the presence of Cu was found to increase the lifetime of DT states from 60 to 100 ns probably due to a decrease in coupling of electron and hole states involved in this emission upon Cu doping. Synthesis of such stable, doped samples along with a better understanding of charge carrier dynamics is significant for emerging optical applications of these NCs.

Optical properties of Cu ions‐doped ZnSe quantum dots in silicate glasses

“…Introduction of Cu 2 O or CuO into the glasses as copper source leads to almost identical emission spectra (Figure B). However, it has been reported that the energy gap (ΔE) between the Cu‐state trapping level and the valence band of ZnSe QDs is ~0.7 eV for Cu + dopants and ~0.3 eV for Cu 2+ dopants . Based on the absorption and emission spectra of CU10, CU25 and CU50 glasses, the ΔE values are found to be 0.5‐0.7 eV, very close to the values obtained from Cu + ‐doped ZnSe QDs.…”

“…Energy dispersive X‐ray spectroscopic analysis of the nanocrystal marked by white circle in Figure B confirms the presence of zinc, selenide and copper in the nanocrystal marked by the white circle (Figure D). The similar ionic radii between 4 coordinated copper ions (77 pm) and zinc ions (74 pm), and 4 coordinated structure of copper ions and zinc ions in ZnSe nanocrystals as confirmed by extended X‐ray absorption fine structure analysis, indicate that copper ions also substitute the zinc sites in the ZnSe nanocrystals formed in the glass.…”

Photoelectrochemical cell studies of Fe2+ doped ZnSe nanorods using the potentiostatic mode of electrodeposition

“…It provides an accessible evaluation of absorption of photons, leading to an excitation of an electron from the valence band to the conduction band, which is finally related with the band gap energy (E g ). The band gap energy and Bohr exciton radius of the bulk ZnSe are 2.69 eV (at 461 nm) and 4.5 nm, respectively [26]. From Fig.…”

“…But at 1.5% Fe 2+ doping in the ZnSe, it is observed that the emissions located at 458 and 506 nm. These peaks are shifted to blue end due to more Fe 2+ percent [26]. The emission peaks at 470 nm and 458 nm are due to band to band transitions.…”

Synthesis and Characterization of Copper-Doped Zinc Selenide Quantum Dots as Fluorescence Probes for Sparfloxacin

“…Figure 8 shows the absorption of copper-doped zinc selenide quantum dots occurs at 350 nanometers with a blue shift and enhanced absorption compared to zinc selenide quantum dots. The copper-doped zinc selenide quantum dots have been reported to have fewer surface defects, a more compact structure, and better optical properties compared with the undoped zinc selenide quantum dots (Gul et al 2011). …”