Jingling Li

Spectroscopy of GdAl3(BO3)4: Tm3+ crystal

Tm{sup 3+}:GdAl{sub 3}(BO{sub 3}){sub 4} crystals were grown successfully from K{sub 2}Mo{sub 3}O{sub 10}-B{sub 2}O{sub 3} solvent by using the top seeded solution growth method. The absorption spectra for both {sigma} and {pi} polarizations were presented. The Judd-Ofelt (J-O) intensity parameters were found to be {omega}{sub 2}=4.54x10{sup -20} cm{sup 2}, {omega}{sub 4}=2.25x10{sup -20} cm{sup 2}, and {omega}{sub 6}=3.39x10{sup -20} cm{sup 2}. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Unpolarized and polarized emission spectra were obtained under the excitations of 468 and 797 nm, respectively. This crystal may be preferable for GaAlAs laser pumping.Tm3+:GdAl3(BO3)4 crystals were grown successfully from K2Mo3O10-B2O3 solvent by using the top seeded solution growth method. The absorption spectra for both σ and π polarizations were presented. The Judd-Ofelt (J-O) intensity parameters were found to be Ω2=4.54×10−20cm2,Ω4=2.25×10−20cm2, and Ω6=3.39×10−20cm2. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Unpolarized and polarized emission spectra were obtained under the excitations of 468 and 797 nm, respectively. This crystal may be preferable for GaAlAs laser pumping.

Promising photovoltaic application of multi-walled carbon nanotubes in perovskites solar cells for retarding recombination

A facile spray deposition method was developed to prepare a high-quality perovskite layer under ambient conditions. However, the performance is expected to be further improved with substrate and the hole transport layer (HTL) optimization and device structure, for instance. MWCNTs with incorporated spiro-OMeTAD exhibited Jsc of 22.13 mA cm−2 and PCE of 10.42%. To infer the origin of the increasing Jsc and PCE, the optical absorption performance, charge transfer and recombination performance were investigated. τ, Rct, Rrec as a function of voltage and EIS measurements revealed the lower transfer resistance and recombination rate in PSCs with MWCNTs compared with the PSCs without MWCNTs. The increased resistance in dark conditions and the dark J–V curves explain the slight changes in the Voc. The SEM images showed that there were no MWCNTs aggregated on the surface of the spiro/MWCNTs composite layer and part of MWCNTs was uncovered by spiro-OMeTAD at the interface of HTM and Au electrode. The decreased ID/IG ratio from 0.90 to 0.68 demonstrated the increased interaction between MWCNTs and spiro-OMeTAD.

High luminance of CuInS2-based yellow quantum dot light emitting diodes fabricated by all-solution processing

In this work, all-solution processed, multi-layer yellow quantum dot light emitting diodes (QLEDs), consisting of a hole transport layer of poly(9-vinylcarbazole), emissive layer of CuInS2/ZnS (ZCIS) QDs, and electron transport layer of ZnO nanoparticles, are fabricated. To improve the carrier-balance in QLEDs, a ligand-exchange strategy is employed to replace n-dodecanethiol that caps the surface of CuInS2/ZnS quantum dots with 2-ethylhexanethiol. After this processing, improvement of current efficiency and external quantum efficiency of QLEDs is achieved. The optimized diodes exhibit a maximum luminance of 2354 cd m−2 and an external quantum efficiency of 0.63%, together with a lower turn-on voltage (decreases from 3.1 V to 2.7 V) using these ligand-exchanged QDs as emitting materials. Furthermore, CuInS2-based QLEDs in our study exhibit color retainability with increasing voltage and prolonged use, and show great promise for practical application.

The growth, thermal and nonlinear optical properties of single-crystal GdAl3(BO3)4

The nonlinear optical single-crystals GdAl3(BO3)4 (GAB), space group R32, were grown by the top-seed solution growth (TSSG) method. The thermal properties and the nonlinear optical characteristics have been investigated. The two principal coefficients of thermal expansion along (100) and (001) were measured to be 5.30 × 10−6, 1.88 × 10−5 K−1. The transmission spectrum was measured and the second-harmonic generation (SHG) was presented. By way of our designed cross superimposed laser crystal multiplier, the frequency doubling laser at wavelength 457.5 nm was measured to be 18.2 mW and the facular properties indicated the multiplier contributed to the improvement of the frequency doubling conversion efficiency.

Enhanced Photovoltaic Performance with Carbon Nanotubes Incorporating into Hole Transport Materials for Perovskite Solar Cells

In an attempt to further enhance the photovoltaic performance of perovskite solar cells (PSCs) fabricated by spray deposition under ambient conditions, carbon nanotubes (CNTs) are introduced for incorporation into hole transport materials (HTM). The effect of CNT category and length on the efficiency of the perovskite solar cell for incorporation into HTM is investigated. The enhanced photovoltaic performance is achieved in multi-walled carbon nanotubes (MWCNTs) with the shortest length. The efficiency of acid-treated MWCNT-based cells is improved compared to that of purified MWCNTs due to the better dispersibility and the π–π interaction between the –COOH group and spiro-OMeTAD. As the volume ratio of the spiro-OMeTAD and spiro/MWCNTs mixture is 2:2 or 3:1, the highest power conversion efficiency (PCE) of PSCs containing MWCNTs reaches 8.7% with the enhanced short-circuit current density (Jsc) and open-circuit voltage (Voc).

Improved performance of quantum dot light emitting diode by modulating electron injection with yttrium-doped ZnO nanoparticles

In a typical light emitting diode (QD-LED), with ZnO nanoparticles (NPs) serving as the electron transport layer (ETL) material, excessive electron injection driven by the matching conduction band maximum (CBM) between the QD and this oxide layer usually causes charge imbalance and degrades the device performance. To address this issue, the electronic structure of ZnO NPs is modified by the yttrium (Y) doping method. We demonstrate that the CBM of ZnO NPs has a strong dependence on the Y-doping concentration, which can be tuned from 3.55 to 2.77 eV as the Y doping content increases from 0% to 9.6%. This CBM variation generates an enlarged barrier between the cathode and this ZnO ETL benefits from the modulation of electron injection. By optimizing electron injection with the use of a low Y-doped (2%) ZnO to achieve charge balance in the QD-LED, device performance is significantly improved with maximum luminance, peak current efficiency, and maximal external quantum efficiency increase from 4918 cd/m2, 11....

Polarized spectroscopic characterization and energy transfer of Tm3+-, Ho3+-BaLaGa3O7: new promising 2.0 µm laser crystals

The growth, absorption spectra, fluorescence spectra and luminescence decay curves of Tm3+-, Ho3+-BaLaGa3O7 crystals are reported. The 3F4→3H6 and 5I7→5I8 IR transitions of the Tm3+-BaLaGa3O7 and Ho3+-BaLaGa3O7 crystals are broad emission bands at about 2.0 µm; the corresponding stimulated emission cross-sections were calculated by the Fuchtbauer–Ladenburg equation, respectively. Based on the Judd–Ofelt theory, we obtained three intensity parameters and a series of spectral parameters. The energy transfer parameters between the Tm and the Ho were also calculated. These results show that these crystals are promising as tunable infrared laser crystals for the 2.0 µm regions.

Spectroscopic properties of Ho3+ doped CaNb2O6 crystal

Abstract Results of the growth and annealing processes of Ho3+:CaNb2O6 crystal with high oxygen defects were reported. The spectroscopic properties of Ho3+:CaNb2O6 were also analysed, and the decay curves of the bulk and powder samples in correspondence with the emission 5I7→5I8 at 2·0 μm were recorded. The effects of radiative trapping on the final results were also indicated, and the final value of the fluorescence lifetimes of 5I7→5I8 transition is calculated to be 5·19 ms. CaNb2O6 crystal was shown to be a prospective material for an infrared laser medium at 2·0 μm.

Highly Solar-Reflective Litchis-Like Core-Shell HGM/TiO2 Microspheres Synthesized by Controllable Heterogeneous Precipitation Method

Hollow glass microsphere (HGM)/TiO2 core-shell structural composites have promising applications in the field of energy efficient solar-reflective paints. In this work, after pretreated with saturated Ca(OH)2 solutions, litchis-like TiO2 shells have been successfully synthesized on HGMs via a controllably heterogeneous precipitation method with Titanium (IV) sulfate (Ti(SO4)2) and urea as reaction precursors. It is emphasized that the use of urea as the precipitating agent is essential for the heterogeneous nucleation and growth of Ti(OH)4 on HGMs, while the Ca(OH)2 pretreatment provides the heterogeneous nucleation sites on HGMs which promotes the nucleation and growth of Ti(OH)4, and gives rise to large secondary Ti(OH)4 particles, leading to the formation of litchis-like TiO2 shells. The resulted core-shell structural HGM/TiO2 microspheres exhibited highest solar reflectance of ∼83%.

Polarized spectral properties and potential application of large-size Nd3+:Ba3Gd2(BO3)4 crystal

The Nd3+-doped Ba3Gd2(BO3)4 crystal with high optical quality and large size is reported in this paper. The growing processes and characteristics of Nd3+:Ba3Gd2(BO3)4 crystal are discussed. The absorption and luminescence spectra of Nd3+ in Ba3Gd2(BO3)4 crystal were measured at room temperature. The luminescence decay curve in correspondence with the 4F3/2 →4I11/2 transition centered at 1062 nm was also measured. The JO intensity parameters Ωt (t = 2,4,6) were calculated to be Ω2 = 1.263, Ω4 = 2.496, Ω6 = 3.606. The radiative lifetime τr and fluorescence lifetime τf are 317.771 and 115 μs respectively, and the fluorescence quantum efficiency is 37.1%.