Multistep Accelerated Aging of Magnetic Field Sensors Based on Nanostructured La–Sr–Mn–O Thin Films
We present results of investigation of accelerated aging influence on electrical resistivity and magnetoresistance (MR) of nanostructured La–Sr–Mn–O films used for magnetic field sensors, which could be applied in advanced scientific and industrial devices. The 400-nm-thick manganite films were grown by metal organic chemical vapor deposition technique. To investigate the effectiveness of accelerated aging, the three methods were tested: 1) thermal treatment of the sensor samples at 100 °C temperature in Ar atmosphere when film surface was uncoated; 2) thermal treatment of the samples coated prior to treatment by polymer; and 3) multistep aging including both previous methods: thermal treatment of the samples with uncoated surface in Ar atmosphere and additional thermal treatment of the coated samples. The sensor samples were studied without and in pulsed magnetic field up to 20 T. To describe the underlying processes, the kinetics of resistivity change during accelerated aging was analyzed using a stretched exponent relaxation function. It was found that the best long-term stability of resistivity in time demonstrated samples treated by a multistep accelerated aging method. All three aging methods resulted in minor influence (<1%) on MR of the films in magnetic fields up to 20 T.
Intrinsic metastability of low doped manganites: La0.8Ca0.2MnO3 case
Abstract.Transport properties of phase separated La0.8Ca0.2MnO3 crystals
in the aged highly resistive metastable state were studied. It was found that the
coexistence of different ferromagnetic phases at low temperatures is sensitive to
electric current/field. In a contrast with the previously studied low resistivity
metastable states the high resistivity state exhibits positive magnetoresistance and
significant current dependence of the resistivity even at temperatures much higher
than the Curie temperature. Application of current pulses results in appearance of
zero bias anomaly in the current dependent conductivity. Similarly to the low
resistivity metastable states the memory of the resistivity can be erased only after
heating of the sample to Te ≈360 K. After one year storage at room
temperature the La0.8Ca0.2MnO3 samples show clear signatures of aging.
The aged samples spontaneously evolute towards high resistivity states. The results
are discussed in the context of a coexistence of two ferromagnetic phases with
different orbital order and different conductivity. The metallic ferromagnetic phase
seems to be less stable giving rise to the experimentally observed electric field
effects and aging. 


Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.