title: Length-dependent change of optical, magnetic, and vibrational properties of vanadate (V(IV)O3(2-)) quantum wire embedded in AM-6 vanadosilicate.
abstract: AM-6 and VSH-1 are vanadosilicates containing VO(3)(2-) quantum wires and oxovanadate [O═VO(4)](2-) quantum dots, respectively. We developed methods to synthesize pure, highly crystalline, monodisperse, and all-V(IV) AM-6 and VSH-1 crystals with sizes between 0.2-0.3 and 10 μm. On the basis of their optical, magnetic susceptibility, vibrational, and electron spin resonance (ESR) properties, we have elucidated the following interesting phenomena. The length of the VO(3)(2-) quantum wire (l) linearly increases as the length along the [110] direction {L([110])} increases. The band gap energy (E(g)) of the VO(3)(2-) quantum wire progressively decreases with increasing l even when it reaches ~210 nm, indicating that the Bohr length (the length at which the quantum confinement effect no longer appears) is longer than 200 nm. The deduced μ(z) and μ(xy) are 0.0005m(e) and 15.7m(e), respectively. Per-V(IV)-ion oscillator strength of the d-d transition increases by 7-9 times and that of CT transition increases by 1.5-1.9 times with increasing l from ~50 to 210 nm (by ~4 times). The longitudinal vibration frequency ν of the VO(3)(2-) quantum wire decreases and the intensity of the vibrational band increases as l increases. The ESR intensity increases while the peak-to-peak width decreases as l increases, indicating that the spin-spin relaxation rate (R(ssr)) decreases as l increases. The magnetic susceptibility χ decreases as l increases, especially at T > 125 K, indicating that the tendency of the d(1) electron spins to orient to the external magnetic field decreases with increasing l.
authors.affiliation: Korea Center for Artificial Photosynthesis, Center for Nanomaterials, and Department of Chemistry, Sogang University, Seoul 121-742, Korea.
authors.forename: Shuvo Jit
authors.initials: SJ
authors.lastname: Datta
authors.forename: Kyung Byung
authors.initials: KB
authors.lastname: Yoon