Structure and luminescence of 2D dilute magnetic semiconductors:: Cd1-xMnxSe•L0.5 (L = diamines)

The two-dimensional (2D) dilute magnetic semiconductors (Cd1-xMnxSeL0.5)-L-. (L = ethylenediamine, or en, and 1,6-hexanediamine, or hda, x = 0-0.8) were synthesized in an autoclave at 120 degrees C. Ab initio structure solution from X-ray powder diffraction reveals the host compound CdSe center dot hda(0.5) (space group, Pbca, a = 6.8852 angstrom, b = 6.7894 angstrom, c = 27.4113 angstrom) is structurally analogous to CdSe center dot en(0.5), except for a subtle difference in alignment of aliphatic diamine ligands-the hda molecule deflects from the c axis and inclines toward the b axis. CdSe center dot 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 mu s) and intrinsic line width (177 meV) at room temperature. When Cd2+ is partly substituted by Mn2+, a strong Mn2+-related luminescence peak at 2.12 eV (584 nm) is obtained at room temperature, which can be assigned to Mn2+ internal transition (T-4(1) -> (6)A(1)); its excitation peak overlaps with the photoemission peak of the 2D exciton ground state which indicates that the Mn2+ emission is driven by the 2D exciton ground-state transition. For x = 0.02, the photoluminescence intensity of Cd1-xMnxSe center dot hda(0.5) reaches maximum and enhances 28 times compared with that of Cd1-xMnxSe center dot en. When x < 0.05, the Mn2+ luminescence is a characteristic single-exponential decay process with a well-defined constant lifetime of 375 mu s. Electron spin resonance spectra show that Mn2+ substitutes Cd2+ ion and forms a [MnSe3N] coordination tetrahedron and that there are isolated Mn2+ luminescence centers in Cd1-xMnxSe center dot hda(0.5) (x < 0.05), which is the key factor for their stronger luminescence character compared to Cd1-xMnxSe center dot en(0.5).