An optical fiber magnetic field sensor using intermodal interferometer coated by magnetic fluid (MF) is proposed. The interferometer consists of down-taper and spherical structure formed on the standard single-mode fiber (SMF) by a fusion splicer. Since the refractive index (RI) of the MF is sensitive to external magnetic field, the interferometer coated by MF can be used for magnetic field sensing. Two interference valleys of the interferometer integrated with ferrofluid under different magnetic field intensities have been experimentally analyzed. The experimental results show that there is a linear relationship between the valley wavelength shift and magnetic field intensity for a range of 0 to 20 mT, and the maximum sensitivity reaches up to −0.195 nm/mT. In the range of 0 to 12 mT, the variation of transmission loss at valley wavelength with a magnetic field has a maximum sensitivity of 0.106 dB/mT.
Free-standing ZnS:Cu and ZnS:Cu,Al quantum dots were prepared in the aqueous medium from readily available
precursors. The construction, morphology and luminescence properties of the ZnS:Cu and ZnS:Cu,Al quantum dots were
evaluated by XRD,TEM and photoluminescence spectra. The average particle size was calculated using the Scherrer
formula to be 5nm, which is also observed from HRTEM image. In PL spectra, 0.7% Cu and 0.4% Cu -doped ZnS:Cu
quantum dots have emission peak around 470 nm and 500 nm, which attributed to the transition from the shallow donor
level (sulfur vacancy) to the e level and t2 level of Cu2+ respectively. And PL spectra of ZnS:Cu,Al quantum dots is
similar with the PL of ZnS:Cu quantum dots, but the luminescence intensity of quantum dots ZnS:Cu,Al increase, which
arise from that Al 3+ ions as co-activated enhance donor level.
Free-standing ZnS:Er and ZnS:Er,Yb quantum dots were prepared in the aqueous medium from readily available
precursors. The construction, morphology and luminescence properties of the ZnS:Er and ZnS:Er,Yb quantum dots were
evaluated by XRD,TEM and photoluminescence spectra. The average particle size was calculated using the Scherrer
formula to be 4nm, which is also observed from HRTEM image. The spectra of ZnS:Er and ZnS:Er,Yb quantum dots
have broad emission between 1450 nm and 1650 nm centered at 1575 nm with the excitation wavelength 980 nm, which
can be attributed to the 4I13/2→4I15/2 transition. But the intensity of ZnS:Er,Yb quantum dots significantly increases with
the addition of Yb as a sensitizing ion into ZnS:Er quantum dots. Because that Yb3+ absorbed the energy and transfer
energy from the 5F5/2 level of the 4I11/2 level (Er3+ ) and improve population accumulation on the 4I11/2 level.
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