Optical and Surface Structural Properties of Mn²⁺-Doped ZnSe Nanoparticles

Abstract

Mn 2+ -doped ZnSe nanoparticles were synthesized from molecular cluster precursors. Four ZnSe nanoparticle samples, one with low Mn 2+ concentration (A), one with an intermediate Mn 2+ concentration (B), one with a high Mn 2+ concentration (C), and one with no Mn 2+ , were prepared and characterized using UV-vis, luminescence, electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) techniques. The sample with no Mn 2+ had a sharp ZnSe band edge emission peak and a quantum yield of ∼2%. The samples with Mn 2+ had a significant decrease in band edge emission. Sample A had no Mn 2+ 4 T 1 f 6 A 1 emission but showed some ZnSe band edge emission and trap state emission. Sample B had Mn 2+ 4 T 1 f 6 A 1 emission and a further reduction in ZnSe band edge emission and trap state emission. Sample C showed an increase in the Mn 2+ 4 T 1 f 6 A 1 emission, a dramatic increase in trap state emission, and essentially no ZnSe band edge emission. The overall emission from all four samples was quenched with time. To better understand these observations, XAFS and ESR data were taken to characterize the local structural and chemical environment of the Mn 2+ ions. The XAFS data indicated that there was a reduction in the Zn and Mn first neighbor Se coordination from the bulk value but a lack of a reduction in the Se first neighbor coordination. This suggests that the core of the nanoparticles resembles that of bulk ZnSe, and the surface of the particle has a higher concentration of metal atoms. We propose that the surface Mn 2+ possessed an octahedral geometry due to significant OH -/O 2coordination and the interior Mn 2+ occupied the Zn 2+ tetrahedral site. The overall low Mn 2+ emission quantum yield (>0.1%) is primarily due to the presence of Mn 2+ on the particle surface, and the decrease in Mn 2+ emission overtime is attributed to the quenching of the luminescence by OH -/O 2coordinated to the surface metal ions. In sample C, which had the highest Mn 2+ concentration, the surface Mn 2+ enhanced the disorder of the nanoparticle surface structure, resulting in an increase in trap state emission.

Magnetic behavior of manganese-doped ZnSe quantum dots

“…Moreover, at least in some of the quantum dots, the Mn-Mn interaction is strong enough to reveal the hyperfine splitting. Signal II may arise due to the location of Mn near the surface 5,11,13 of the ZnSe quantum dot. Signal II is superimposed on signal I, and is originated since Mn 2+ has less of a symmetric environment.…”

“…2 High fluorescence efficiency along with magnetic ordering makes Mn an interesting transition element dopant [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] in the semiconductor nanoparticles. Recently, Mn-doped ZnSe nanoparticles [3][4][5][6][7][8][9][10] received much attention since it has the potential application for luminescent as well as spintronic devices. 1 Moreover, the number of Mn ions incorporated at substitutional sites can also modify the lattice parameters as well as the band gap of semiconducting materials.…”

“…1 Moreover, the number of Mn ions incorporated at substitutional sites can also modify the lattice parameters as well as the band gap of semiconducting materials. Additionally, the Mn-related electron paramagnetic resonance ͑EPR͒ signal is strong 3,5,11 in the ternary compounds and has been modeled for various chemical environments. However, the large variations in magnetic properties of doped quantum dots have been reported, and the role of the synthesis route in chemically controlled magnetic effects has been identified.…”

Luminescence properties of the solvothermally synthesized blue light emitting Mn doped Cu2O nanoparticles

“…The PLE result collected by monitoring the Mn 2+ 4 T 2 → 6 A 1 transition also indicate, that energy transfer from the photoexcited Cu 2 O nanocrystals to the Mn 2+ gives rise to the blue emission. 20,39 The UV-visible absorption spectrum of sample HMnCP3 shown in the Fig. 4͑d͒, gives a weak broad peak at 632 nm ͑1.96 eV͒ along with four absorption bands at about 280, 293, 334, and 352 nm.…”

“…18,19 The engineering of band gap and influencing physical, chemical, and electronic properties of the semiconductors are possible by the use of the right dopants. Norman et al 20 showed the tuning of the emission energy of Mn doped ZnSe nanoparticles. The band gap tuning of the Mn doped CdS quantum dots were observed by Kim.…”