Journal of the American Chemical Society, Vol.134, No.41, 17202-17211, 2012
Length-Dependent Change of Optical, Magnetic, and Vibrational Properties of Vanadate ((VO32-)-O-IV) Quantum Wire Embedded in AM-6 Vanadosilicate
AM-6 and VSH-1 are vanadosilicates containing VO32- quantum wires and oxovanadate [O=VO4](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 mu m. 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 VO32- quantum wire (l) linearly increases as the length along the [110] direction {L-[110]} increases. The band gap energy (E-g) of the VO32- quantum wire progressively decreases with increasing l even when it reaches similar to 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 mu(z) and mu(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 I from similar to 50 to 210 nm (by similar to 4 times). The longitudinal vibration frequency nu of the VO32- quantum wire decreases and the intensity of the vibrational band increases as 1 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 chi decreases as l increases, especially at T > 125 K, indicating that the tendency of the d(l) electron spins to orient to the external magnetic field decreases with increasing l.