Structure and Luminescence of 2D Dilute Magnetic Semiconductors:  Cd1 - x Mn x Se·L0.5 (L = Diamines)

• Published in: Chemistry of materials Vol. 17; no. 7; pp. 1698 - 1703
• Main Authors: Lu, Jun, Wei, Shuo, Yu, Weichao, Zhang, Houbo, Qian, Yitai
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05.04.2005
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm048339y

The two-dimensional (2D) dilute magnetic semiconductors Cd1 - x Mn x Se·L0.5 (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 ligandsthe hda molecule deflects from the c axis and inclines toward the b axis. CdSe·L0.5 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 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 (4T1 → 6A1); 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 - x Mn x Se·hda 0.5 reaches maximum and enhances 28 times compared with that of Cd1 - x Mn x Se·en. When x < 0.05, the Mn2+ luminescence is a characteristic single-exponential decay process with a well-defined constant lifetime of 375 μs. 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 - x Mn x Se·hda 0.5 (x < 0.05), which is the key factor for their stronger luminescence character compared to Cd1 - x Mn x Se·en 0.5.