Gram-Scale Synthesis of Hydrophilic PEI-Coated AgInS₂ Quantum Dots and Its Application in Hydrogen Peroxide/Glucose Detection and Cell Imaging

Assisted with polyethylenimine, 4.0 L of water-soluble AgInS₂ quantum dots (AIS QDs) were successfully synthesized in an electric pressure cooker. As-prepared QDs exhibit yellow emission with a photoluminescence (PL) quantum yield up to 32%. The QDs also show excellent water/buffer stability. The highly luminescent AIS QDs are used to explore their dual-functional behavior: detection of hydrogen peroxide (H₂O₂)/glucose and cell imaging. The amino-functionalized AIS QDs show high sensitivity and specificity for H₂O₂ and glucose with detection limits of 0.42 and 0.90 μM, respectively. A linear correlation was established between PL intensity and concentration of H₂O₂ in the ranges of 0.5–10 μM and 10–300 μM, while the linear ranges were 1–10 μM and 10–1000 μM for detection of glucose. The AIS QDs reveal negligible cytotoxicity on HeLa cells. Furthermore, the luminescence of AIS QDs gives the function of optical imaging

Tuning the Band Gap of Cu₂ZnSn(S,Se)₄ Thin Films via Lithium Alloying

Alkali metal doping plays a crucial role in fabricating high-performance Cu­(In,Ga)­(S,Se)₂ and Cu₂ZnSn­(S,Se)₄ (CZTSSe) thin film solar cells. In this study, we report the first experimental observation and characterizations of the alloyed Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄ thin films. It is found that Cu⁺ ions in Cu₂ZnSn­(S,Se)₄ thin films can be substituted with Li⁺ ions, forming homogeneous Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄ (0 ≤ <i>x</i> ≤ 0.29) alloyed thin films. Consequently, the band gap, conduction band minimum, and valence band maximum of Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄ thin films are profoundly affected by Li/Cu ratios. The band alignment at the Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄/CdS interface can be tuned by changing the Li/Cu ratio. We found that the photovoltaic parameters of the Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄ solar cell devices are strongly influenced by the Li/Cu ratios. Besides, the lattice constant, carrier concentration, and crystal growth of Li_<i>x</i>Cu_2–<i>x</i>ZnSn­(S,Se)₄ thin films were studied in detail

Scaling up the Aqueous Synthesis of Visible Light Emitting Multinary AgInS₂/ZnS Core/Shell Quantum Dots

Approximately 3 g of water-soluble AgInS₂/ZnS core/shell quantum dots (AIS/ZnS QDs) with a maximum photoluminescence quantum yield of up to 39.1% was synthesized in an aqueous solution of gelatin and thioglycolic acid (TGA). The composition of the AIS QDs could be readily adjusted by controlling the molar ratio of the starting Ag/In precursors in the reaction solution, which leads to a tunable emission ranging from 535 to 607 nm. The as-prepared core/shell QDs exhibit excellent photostability and water/buffer stability. More importantly, these cadmium-free hydrophilic AIS/ZnS core/shell QDs are biocompatible and can be directly utilized in cancer cell imaging

Facile and Low-Cost Sodium-Doping Method for High-Efficiency Cu₂ZnSnSe₄ Thin Film Solar Cells

We present a simple and low-cost sodium-doping method for Cu₂ZnSnSe₄ (CZTSe) thin film solar cells. In this method, a piece of soda-lime glass (SLG) is served as the sodium source and is placed on top of the CZTSe precursor thin film during selenization. It was observed that the grain growth and the hole-carrier concentration can be significantly improved by the diffusion of sodium from the top SLG. Through this approach, high-quality CZTSe absorber layer is obtained after the selenization, and the photoelectric conversion efficiencies (PCE) of 7.51% and 6.09% are achieved for CZTSe thin film solar cells deposited on a Mo-coated SLG substrate and a Mo-coated quartz substrate, respectively. The difference in PCE on SLG and quartz substrate revealed that Na diffusion from the bottom SLG substrate and the top SLG was most effective for the high-performance of CZTSe solar cell devices

Warm White Light Emitting Diodes with Gelatin-Coated AgInS₂/ZnS Core/Shell Quantum Dots

Cadmium-free and water-soluble AgInS₂/ZnS core/shell quantum dots (QDs) with a cost of 2.5 $/g are synthesized in an electric pressure cooker. The QD powders with different Ag/In ratios exhibit bright yellow, orange, and orange-red luminescence under UV light. Their absolute photoluminescence quantum yields (PLQYs) can reach as high as 50.5, 57, and 52%, respectively. Because gelatin is used as the capping agent, the concentrated QDs/gelatin solution can be directly utilized as phosphor for the fabrication of white light-emitting diodes (LEDs) by a simple drop-drying process without the need of resin package. Warm-white LEDs are obtained by combining orange-emitting QDs with blue InGaN chip. As-fabricated warm-white LED exhibits a luminous efficacy of 39.85 lm/W, a correlated color temperature (CCT) of 2634 K and a color rendering index (CRI) of 71 at a drive current of 20 mA. Furthermore, the electroluminescence (EL) stability of LED device and thermal stability of as-prepared QDs are evaluated

Hydrothermal Derived LaOF:Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) Nanocrystals with Multicolor-Tunable Emission Properties

A series of LaOF:Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) nanocrystals with good dispersion have been successfully prepared by the hydrothermal method followed a heat-treatment process. Under ultraviolet radiation and low-voltage electron beam excitation, the LaOF:Ln³⁺ nanocrystals show the characteristic f-f emissions of Ln³⁺ (Ln = Eu, Tb, Sm, Dy, Tm, or Ho) and give red, blue-green, orange, yellow, blue, and green emission, respectively. Moreover, there exists simultaneous luminescence of Tb³⁺, Eu³⁺, Sm³⁺, Dy³⁺, Tm³⁺, or Ho³⁺ individually when codoping them in the single-phase LaOF host (for example, LaOF:Tb³⁺, Eu³⁺/Sm³⁺; LaOF:Tm³⁺, Dy³⁺/Ho³⁺; LaOF:Tm³⁺, Ho³⁺, Eu³⁺ systems), which is beneficial to tune the emission colors. Under low-voltage electron beam excitation, a variety of colors can be efficiently adjusted by varying the doping ions and the doping concentration, making these materials have potential applications in field-emission display devices. More importantly, the energy transfer from Tm³⁺ to Ho³⁺ in the LaOF:Tm³⁺, Ho³⁺ samples under UV excitation was first investigated and has been demonstrated to be a resonant type via a quadrupole-quadrupole mechanism. The critical distance (<i>R</i>_Tm–Ho) is calculated to be 28.4 Å. In addition, the LaOF:Tb³⁺ and LaOF:Tm³⁺ phosphors exhibit green and blue luminescence with better chromaticity coordinates, color purity, and higher intensity compared with the commercial green phosphor ZnO:Zn and blue phosphor Y₂SiO₅:Ce³⁺ to some extent under low-voltage electron beam excitation

Luminescence and Energy Transfer Properties of Ca₂Ba₃(PO₄)₃Cl and Ca₂Ba₃(PO₄)₃Cl:A (A = Eu²⁺/Ce³⁺/Dy³⁺/Tb³⁺) under UV and Low-Voltage Electron Beam Excitation

Pure Ca₂Ba₃(PO₄)₃Cl and rare earth ion (Eu²⁺/Ce³⁺/Dy³⁺/Tb³⁺) doped Ca₂Ba₃(PO₄)₃Cl phosphors with the apatite structure have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD) and structure refinement, photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. Under UV light excitation, the undoped Ca₂Ba₃(PO₄)₃Cl sample shows broad band photoluminescence centered near 480 nm after being reduced due to the defect structure. Eu²⁺ and Ce³⁺ ion doped Ca₂Ba₃(PO₄)₃Cl samples also show broad 5d → 4f transitions with cyan and blue colors and higher quantum yields (72% for Ca₂Ba₃(PO₄)₃Cl:0.04Eu²⁺; 67% for Ca₂Ba₃(PO₄)₃Cl:0.016Ce³⁺). For Dy³⁺ and Tb³⁺ doped Ca₂Ba₃(PO₄)₃Cl samples, they give strong line emissions coming from 4f → 4f transitions. Moreover, the Ce³⁺ ion can transfer its energy to the Tb³⁺ ion in the Ca₂Ba₃(PO₄)₃Cl host, and the energy transfer mechanism has been demonstrated to be a resonant type, via a dipole–quadrupole interaction. However, under the low voltage electron beam excitation, Tb³⁺ ion doped Ca₂Ba₃(PO₄)₃Cl samples present different luminescence properties compared with their PL spectra, which is ascribed to the different excitation mechanism. On the basis of the good PL and CL properties of the Ca₂Ba₃(PO₄)₃Cl:A (A = Ce³⁺/Eu²⁺/Tb³⁺/Dy³⁺), Ca₂Ba₃(PO₄)₃Cl might be promising for application in solid state lighting and field-emission displays

Homogeneous Synthesis and Electroluminescence Device of Highly Luminescent CsPbBr₃ Perovskite Nanocrystals

Highly luminescent CsPbBr₃ perovskite nanocrystals (PNCs) are homogeneously synthesized by mixing toluene solutions of PbBr₂ and cesium oleate at room temperature in open air. We found that PbBr₂ can be easily dissolved in nonpolar toluene in the presence of tetraoctylammonium bromide, which allows us to homogeneously prepare CsPbBr₃ perovskite quantum dots and prevents the use of harmful polar organic solvents, such as <i>N</i>,<i>N</i>-dimethylformamide, dimethyl sulfoxide, and <i>N</i>-methyl-2-pyrrolidone. Additionally, this method can be extended to synthesize highly luminescent CH₃NH₃PbBr₃ perovskite quantum dots. An electroluminescence device with a maximal luminance of 110 cd/m² has been fabricated by using high-quality CsPbBr₃ PNCs as the emitting layer

Blue Emitting Ca₈La₂(PO₄)₆O₂:Ce³⁺/Eu²⁺ Phosphors with High Color Purity and Brightness for White LED: Soft-Chemical Synthesis, Luminescence, and Energy Transfer Properties

Ce³⁺ and/or Eu²⁺ activated Ca₈La₂(PO₄)₆O₂ (CLPA) oxyapatite blue phosphors have been prepared via a Pechini-type sol–gel process. X-ray diffraction (XRD), photoluminescence (PL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. The emission of Ce³⁺ and Eu²⁺ ions at different lattice sites has been identified and discussed. The CLPA:0.04Ce³⁺ phosphor exhibits bright blue emission with higher quantum yield (67%) and excellent CIE coordinates (<i>x</i> = 0.160, <i>y</i> = 0.115) under UV excitation, and the CLPA:0.05Eu²⁺ phosphor also exhibits blue emission with CIE coordinates (0.187, 0.164). The energy transfer from Ce³⁺ to Eu²⁺ in CLPA:Ce³⁺/Eu²⁺ phosphors has been validated and demonstrated to be a resonant type via a dipole–dipole mechanism. The critical distance (<i>R</i>_c) of Ce³⁺ to Eu²⁺ ions in CLPA was calculated (by the spectral overlap method) to be 26.67 Å. The quantum yields of Ce³⁺ and Eu²⁺ coactivated CLPA phosphors are enhanced compared with that of Eu²⁺ activated samples due to energy transfer. The CIE coordinates of CLPA:0.04Ce³⁺, 0.02Eu²⁺ are (0.179, 0.169). The corresponding luminescence and energy transfer mechanisms have been proposed in detail. These blue phosphors might be promising for use in pc-white LEDs

Fabrication of Hollow and Porous Structured GdVO₄:Dy³⁺ Nanospheres as Anticancer Drug Carrier and MRI Contrast Agent

Hollow and porous structured GdVO₄:Dy³⁺ spheres were fabricated via a facile self-sacrificing templated method. The large cavity allows them to be used as potential hosts for therapeutic drugs, and the porous feature of the shell allows guest molecules to easily pass through the void space and surrounding environment. The samples show strong yellow-green emission of Dy³⁺ (485 nm, ⁴F_9/2 → ⁶H_15/2; 575 nm, ⁴F_9/2 → ⁶H_13/2) under UV excitation. The emission intensity of GdVO₄:Dy³⁺ was weakened after encapsulation of anticancer drug (doxorubicin hydrochloride, DOX) and gradually restored with the cumulative released time of DOX. These hollow spheres were nontoxic to HeLa cells, while DOX-loaded samples led to apparent cytotoxicity as a result of the sustained release of DOX. ICP measurement indicates that free toxic Gd ions can hardly dissolate from the matrix. The endocytosis process of DOX-loaded hollow spheres is observed using confocal laser scanning microscopy (CLSM). Furthermore, GdVO₄:Dy³⁺ hollow spheres can be used for <i>T</i>₁-weighted magnetic resonance (MR) imaging. These results implicate that the luminescent GdVO₄:Dy³⁺ spheres with hollow and porous structure are promising platforms for drug storage/release and MR imaging