The two-dimensional (2D) dilute magnetic semiconductors Cd 1-x Mn x Se‚L 0.5 (L ) ethylenediamine, or en, and 1,6-hexanediamine, or hda, x ) 0-0.8) were synthesized in an autoclave at 120 °C. Ab initio structure solution from X-ray powder diffraction reveals the host compound CdSe‚hda 0.5 (space group, Pbca, a ) 6.8852 Å, b ) 6.7894 Å, c ) 27.4113 Å) is structurally analogous to CdSe‚en 0.5 , except for a subtle difference in alignment of aliphatic diamine ligandssthe hda molecule deflects from the c axis and inclines toward the b axis. CdSe‚L 0.5 shows well-defined UV absorption and emission peaks, which is attributed to a 2D exciton band edge transition due to size confinement effect in the c direction and the only photoemission level is the 2D exciton ground state with a long lifetime (7 µs) and intrinsic line width (177 meV) at room temperature. When Cd 2+ is partly substituted by Mn 2+ , a strong Mn 2+ -related luminescence peak at 2.12 eV (584 nm) is obtained at room temperature, which can be assigned to Mn 2+ internal transition ( 4 T 1 f 6 A 1 ); its excitation peak overlaps with the photoemission peak of the 2D exciton ground state which indicates that the Mn 2+ emission is driven by the 2D exciton ground-state transition. For x ) 0.02, the photoluminescence intensity of Cd 1-x Mn x Se‚hda 0.5 reaches maximum and enhances 28 times compared with that of Cd 1-x Mn x Se‚en. When x < 0.05, the Mn 2+ luminescence is a characteristic single-exponential decay process with a well-defined constant lifetime of 375 µs. Electron spin resonance spectra show that Mn 2+ substitutes Cd 2+ ion and forms a [MnSe 3 N] coordination tetrahedron and that there are isolated Mn 2+ luminescence centers in Cd 1-x Mn x Se‚hda 0.5 (x < 0.05), which is the key factor for their stronger luminescence character compared to Cd 1-x Mn x Se‚en 0.5 .
The two-dimension dilute magnetic semiconductors (2D-DMS) Zn1
-
x
Mn
x
Se·0.5L (L = ethylenediamine or
en, 1,3-propanediamine or pda, 1,4-butanediamine or bda, and 1,6-hexanediamine or hda) and their host
compounds ZnSe·0.5L were prepared by solvothermal reaction in solvent L at 190 °C. The powder X-ray
diffraction patterns of ZnSe·0.5L are indexed as isomorphous orthorhombic lattices, whose constants c increase
monotonically from L = en to L = hda. The orthorhombic lattice in ab plane of ZnSe·0.5en is a shrunken
2D superlattice (√3a×c) of the (110) plane of hexagonal ZnSe. When Zn2+ is partly substituted by Mn2+,
Zn1
-
x
Mn
x
Se·0.5L become 2D-DMS. Their photoluminescence (PL) spectra show strong Mn2+-related emission
peaks at 2.07 eV (600 nm). The Mn content dependence of PL intensity of Zn1
-
x
Mn
x
Se·0.5hda is especially
studied, and high intensities are obtained when x < 0.2. For x ≈ 0.2, the PL intensities of Zn1
-
x
Mn
x
Se·0.5L
increase from L = en to L = hda, which can be attributed to the formation of Zn/Mn−N bonds and the
effective energy transfer routes and radiative recombination of the 3d electron of Mn2+ within the 2D
[Zn1
-
x
Mn
x
Se] layers.
In the presence of surfactant, potassium stearate, quantum-confined InP nanocrystals (NCs) were hydrothermally synthesized in aqueous ammonia. Powder x-ray diffraction (XRD) patterns give the zinc blende phase of InP with lattice constant a=5.8377±8×10−4 Å. Transmission electron microscopy (TEM) micrographs show that the as-prepared InP NCs are spherical secondary particles (120 nm) consisting of spherical nanocrystals and rod-like nanocrystals grown in the direction perpendicular to the [111] direction, which is different from those grown by solution–liquid–solid process. X-ray photoelectron spectra indicate that the nanocrystals have a stoichiometric ratio of In:P=1.2:1 and their surfaces are capped with stearate ions. Powder XRD, TEM images, Raman spectra, optical absorption and photoluminescence spectra of InP NCs grown with surfactant were compared with those of the InP NCs grown without surfactant, and it indicated that the as-prepared InP NCs via surfactant-aided synthesis are quantum confined: their transverse optical and longitudinal optical vibration modes exhibit frequency redshifting and asymmetric broadening which is consistent with the phonon confinement model of nanoparticles. Compared with bulk values, InP NCs exhibit a band-edge emission band centered at 1.81 eV (685 nm) with a blueshift of 0.44 eV at 300 K. A wide distribution in size and the two-morphology nature of the NCs resulted in featureless absorption spectra and broadening of the emission band. The formation mechanism of the InP NCs is discussed and attributed to an in situ decomposition process of an indium polyphosphide amorphous precursor.
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