Intense single-band red upconversion emission in BiOCl:Er3+ layered semiconductor via co-doping Ho3+

Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions(RE3+) doped upconversion(UC) materials is still desirable.In this work,the intense single-band red emission is achieved by co-doping only Ho3+in the BiOCl:Er3+ under 1550 nm excitation.In the BiOCl layered host,co-doping Ho3+can further enhance the red emission and simultaneously suppress the green emission of Er3+,and thus obviously improve the red-to-green(R/G) ratio.It is found that Ho3+does not se rve as ene rgy trapping through the 5 I6 state as in traditional UC materials but acts as ET bridge(4 S3/2,2 H11/2(Er3+)→5 F4,5 S2(Ho3+)→4 F9/2(Er3+)).The tuning mechanism of Ho3+is discussed in detail and further confirms through a comparative experiment.Our research gives an unusual perspective to tune the UC behavior of Er3+through co-doping Ho3+,which might be inspiring for achievement of single-band red UC emission.

Boosting single-band red upconversion luminescence in colloidal NaErF_4 nanocrystals:Effects of doping and inert shell

Single-band red upconversion luminescence(UCL) is vital to in vivo bioimaging as well as "see and treat" biomedicines. Herein, starting with the previously reported β-NaErF4:Tm UCNPs, we examined the effects of both Yb^(3+) doping and inert shell coating on the red-to-green(R/G) ratio for Er3+ based UCL. The doping of Yb^(3+) into the β-NaErF4:Tm3+ core not only enhances the whole UCL intensity, but also raises the R/G ratio by 1.25 times. In addition, the coating of an inert NaYF4 shell, which is usually adopted for the enhancement of UCL intensity, further boosts the R/G value up to as high as 77.92. This work may benefit the potential bioimaging application of single-band red UCL.

Controllable precision of the projective truncation approximation for Green's functions

Recently, we developed the projective truncation approximation for the equation of motion of two-time Green's functions(Fan et al., Phys. Rev. B 97, 165140(2018)). In that approximation, the precision of results depends on the selection of operator basis. Here, for three successively larger operator bases, we calculate the local static averages and the impurity density of states of the single-band Anderson impurity model. The results converge systematically towards those of numerical renormalization group as the basis size is enlarged. We also propose a quantitative gauge of the truncation error within this method and demonstrate its usefulness using the Hubbard-I basis. We thus confirm that the projective truncation approximation is a method of controllable precision for quantum many-body systems.

Multi-Band Bandpass Filter Using Novel Topology for Next-Generation IoT Wireless Systems

The design of single-and quad-band Bandpass Filter(BPF)topology has been presented in this paper for next-generation Internet of Things(IoT)devices.The main topology is constructed using the Split Ring Resonator(SRR),separated by the Anti-Parallel Coupled Line Structure(APCLS).A detailed analysis of APCLS has been presented,which is further used to construct the single-and quad-band BPF.The single-band BPF design consists of SRR loaded with APCLS.The developed single-band BPF displays a dual-mode response with a center frequency of 2.65 GHz and a measured fractional bandwidth of 17.17%.Moreover,a quad-band bandpass filter has been achieved using the same topology with minor modification in the SRR and APCLS electrical parameters.The developed quad-band BPF generates a dual-mode response having center frequencies of 1.2,2.4,3.5,and 4.7 GHz with the measured fractional bandwidth of 13%,26%,16%,and 5%,respectively.Two prototypes have been fabricated on the highfrequency substrate to validate the proposed topologies.Very high rejection in the stopbands region,little in-band insertion loss,and very selective passband have been measured for single-and quad-band BPFs.The measured and simulated results are well correlated.

Dual Band BPF Based on Parallel Coupled Lines Loaded by Open Stubs for Ku-Band Satellite Applications

This paper presents a dual band Band Pass Filter (BPF) operating at both the downlink and uplink frequency bands for Ku-band satellite applications. The commonly used frequency band in mobile communications satellites is the Ku-band. These mobile satellite systems help connect remote regions, vehicles, ships, people and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems. The structure of the proposed filter is based on parallel coupled microstrip lines and four sections are used. Tuning the two operational bands can be achieved using two open-circuited stubs at the first and last sections of the parallel coupled microstrip lines. The proposed filter is adjusted to operate at 12.54 GHz and 14.14 GHz for downlink and uplink bands, respectively. The proposed dual band BPF is fabricated, measured, and good agreement is obtained between simulated and measured results.

Advances in Methods of Surface Water Extraction Based on MODIS Data

In recent years,remote sensing technology has been widely used to distinguish and extract water body information on the surface of land,investigate and analyze surface water resources,monitor and study ecological environment,monitor and assess floods. Remote sensing data provided by MODIS sensor carried on satellites in the United States Earth Observation System（ EOS） have high spatial and temporal resolution and spectral resolution,and images have a wide coverage range and are available for free. Moreover,they can be used for dynamic monitoring of changes in water body area on the earth quickly and efficiently. In this study,based on the analysis of spectral characteristics of water body,the characteristics of MODIS data and the methods of surface water extraction were introduced,and the advantages and disadvantages of various methods of water body extraction were analyzed by the comparison between the practical application effects of these methods.