Transport properties of underdoped
Nd2−xCexCuO4−δ
single crystals with different oxygen contents have been investigated
systematically. In-plane resistivity begins to decrease at a certain temperature
T*
(pseudogap opening); at the same temperature the out-of-plane resistivity shows
a more apparent decrease, in contrast to the hole-doped cuprates. Around
T*, the curvature changes
the sign for both ρab(T)
and ρc(T). Decrease of oxygen content results in a sign change of the curvature
from negative to positive at high temperature for the crystals with
x close
to 0.15. T*
decreases with increasing doping level and decreasing oxygen content, while the anisotropy
increases, different from hole-doped cuprates. The pseudogap can only be observed in the
underdoped regime for n-type cuprates; the change of oxygen content can just modify the
pseudogap opening temperature.
A new green luminescent phosphor, Li(Y 1-x Tb x )GeO 4 , was prepared using a hightemperature solid-phase method. The X-ray diffraction (XRD) measured spectrum agreed well with the standard card JCPDS No. 02-3479, indicating that it is a quaternary compound belonging to the space group of Pnma( 62) with an orthogonal crystalline phase; the excitation and emission spectra measured using the phosphor spectrometer showed that it can be effectively excited by near-ultraviolet light at 378 nm and blue light at 482 nm, and produced excellent strong emission of green light at 550 nm. The afterglow test results show that the sample had a good long afterglow effect at lower doping concentrations; the thermal stability test results showed that its thermal burst activation energy ΔE ≈ 0.37 eV had its excellent thermal stability. The rare earth Tb 3+ -doped green phosphor, LiYGeO 4 :Tb 3+ , has potential applications in household lighting, medical therapy, and optical storage.
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