Brightness and Lifetime Improved Light-Emitting Diodes from Sr-Doped Quasi-Two-Dimensional Perovskite Layers

Green Perovskite Light-Emitting Diodes(PeLEDs)have attracted wide attention for full spectrum displays.However,the inferior film morphology and luminescence property of quasi-two-dimensional(quasi-2D)perovskite layers limit the photoelectric property of the PeLEDs.In this paper,the effect of strontium(Sr)doped in quasi-2D perovskite layers is investigated to obtain a high-quality active layer.The morphologies and optical properties of Sr-doped quasi-2D perovskite films with different concentrations are studied.With the addition of strontium,more low-dimensional-layer perovskite phases(n D 2 and n D 3)appear in quasi-2D perovskite films,providing efficient intraband carrier funneling pathway and facilitating radiative recombination.The photoluminescence(PL)peak intensity of optimized Sr-doped quasi-2D perovskite layers increases 50%compared with the non-strontium counterpart.Moreover,green PeLEDs based on a Sr-doped quasi-2D perovskite layer reach a maximum luminance(Lmax)of 2943.77 cd/m^(2),which is three times of the control device.The electroluminescence(EL)peaks of Maximum External Quantum Efficiency(MEQE)and Lmax of Sr-doped PeLEDs exhibite a slight shift,indicating the excellent stability and performance of Sr-doped devices.The optimized device can continuously operate for 360 s at MEQE driving voltage,resulting in a half-lifetime of60 s,which is 3-fold greater than that of the control PeLEDs.

The Effect on the Electric Structure and Optical Properties of Ca2Ge Bulk with Sr-Doping

The electronic structure and the optical properties of Ca2Ge have been calculated by the first-principles pseudo potential method. The results of the electric structure show that Ca2Ge bulk is a direct semiconductor with the band gap of 0.306 eV, the conduction band is mainly composed of Ca 3d, the valence bands is mainly composed of Ge 3p. With Sr-doping, Ca2Ge bulk is a direct semiconductor with the band gap of 0.350 eV, the conduction bands are mainly composed of Ca 3d and Sr 3d, the valence bands are mainly composed of Ge 3p and Sr 3d. The results of the optical properties show that the dielectric constant of Ca2Ge bulk is reduced from 21.52 to 13.94, the reflectivity is decreased, and the absorption is increased with Sr-doping. The optical properties are improved with Sr-doping, the results offer theoretical guide for the optical properties control of Ca2Ge.

Sr-doping effects on conductivity,charge transport,and ferroelectricity of Ba_(0.7)La_(0.3)TiO_(3) epitaxial thin films

Sr-doped Ba_(0.7)La_(0.3)TiO_(3)(BSLTO)thin films are deposited by pulsed laser deposition,and their microstructure,conductivity,carrier transport mechanism,and ferroelectricity are systematically investigated.The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films,resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements.Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures.For the films with semiconducting behavior,the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases.The metalic conductive behaviors in the films with Sr=0.30,0.40 conform to thermal phonon scattering mode.The difference in charge transport behavior dependent on the A-site cation doping,is clarified.It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping,higher carrier mobility,and lower electrical resistivity.Interestingly,the piezoelectric force microscopy(PFM)results demonstrate that all the BSLTO films can exhibit ferroelectricity,especially for the room temperature metallic conduction film with Sr=0.40.These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.

Reconstruction of Surface Porous PEEK Decorated with Strontium-doped Calcium Phosphate Coatings for Enhancing Osteogenic Activity

The aim of this study was to reconstruct surface porous structure with hundreds of micrometers and then bio-mineralize Sr-doped Calcium Phosphate(Sr-doped CaP)on Polyetheretherketone(PEEK)profile to enhance its bioactivity.A surface porous structure was prepared on PEEK profile by embedding and acid-etching of SiO2 particles as porogen(SP-PEEK).Then the Sr-doped CaP was further decorated on the porous surface after sulfonation,introduction of Sr-doped CaP crystal seeds and bio-mineralization in 1.5 times simulated body fluid(BSSP-PEEK-CaP/Sr).It was feasible to reconstruct the surface porous structure with hundreds of micrometers on PEEK profile by the present method without damaging its mechanical properties.The Sr-doped CaP crystal seeds effectively promoted the bio-mineralization of bio-inertness PEEK.All as-prepared PEEK did not inhibit the proliferation of cells.ALP of bio-mineralized groups was significantly increased than that of the other groups.The BSSP-PEEK-CaP/Sr obviously affected the morphology and promoted the adhesion and spreading of cells.As a result,the cyto-biocompatibity and bioactivity of PEEK were improved after bio-mineralization.Sr-doped CaP on PEEK most likely was beneficial for cells,which was associated with the increasing of the hydrophilicity on PEEK.This study provided a candidate method to improve the osteogenesis of PEEK implants.

Enhanced aging and thermal shock performance of Mn_(1.95-x)Co_(0.21)Ni_(0.84)Sr_(x)O_(4) NTC ceramics

The Mn_(1.95-x)Co_(0.21)Ni_(0.84)Sr_(x)O_(4)(MCNS)(0≤x≤0.15)based negative temperature coefficient(NTC)materials are prepared by co-precipitation method.The replacement of Mn by Sr plays a critical role in controlling the lattice parameter,relative density,microstructure,and electrical properties.The lattice parameter and relative density increase with the increase of Sr content.A small amount of Sr restrains the grain growth and increases the bulk density.Moreover,the room resistivityρ25,material constant B25/50,activation energy Ea,and temperature coefficientαvalues of MCNS ceramics are influenced by the Sr content and ranged in 1535.0–2053.6Ω·cm,3654–3709 K,0.3149–0.3197 eV,and(–4.173%)–(–4.111%),respectively.The X-ray photoelectron spectroscopy(XPS)results explain the transformation of MCNS ceramics from n-to p-type semiconductors.The conduction could arise from the hopping polaron between Mn3+/Mn4+and Co^(2+)/Co^(3+) in the octahedral sites.The impedance data analysis also discusses the conduction mechanism of the MCNS ceramic,whereas grain resistance dominates the whole resistance of the samples.Furthermore,the aging coefficient(△R/R)of MCNS ceramics is found to be<0.2%,which indicates the stable distribution of cations in the spinel.Finally,the MCNS ceramics demonstrate excellent thermal durability with<1.3%of resistance shift after 100 thermal shock cycles.

Enhancing the dielectric and piezoelectric properties of Pb_(0.99)Gd_(0.01)Zr_(0.53)Ti_(0.47)O_(3) ferroelectric ceramics by Sr-doping

Recently,high-performance lead zirconate titanate(Pb(Zr_(1-x)Ti_(x))O_(3),PZT)ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range,better temperature stability,as well as larger piezoelectric properties and higher energy conversion efficiency.In this study,the perovskite-type ferroelectric ceramics with a chemical formula of Pb_(0.99-x)Gd_(0.01)Sr_(x)Zr_(0.53)Ti_(0.47)O_(3)(x=0 and 0.02,abbr.PGZT and PGSZT,respectively)were prepared by the traditional solid-state reaction route.The influences of Sr-doping on the phase structure,dielectric properties,ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated.The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10 Hz and temperature range of 20–100℃.The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT,but also decreases its dielectric loss tangent,with the d_(33) value of 473 pC/N,ε_(r) value of 1586 and tanδvalue of 0.016 found in PGSZT.Also,PGSZT shows a high Curie temperature(T_(C))of 350℃.The underlying mechanisms of the property enhancement were identified as that the introduced Sr^(2+) replaces the volatile Pb^(2+) located at the A-site of the perovskite structure,thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics,consequently enhancing the dielectric and piezoelectric properties of PGZT.On the other hand,the frequency change in the low-frequency range(<1 Hz)played a significant impact on the remanent polarization(P_(r))and internal biased electric field(E_(i))of PGSZT,but the frequency dependence of coercive field(E_(c))tends to diminish in the high-frequency range(≥1 Hz).