Lanthanide-based luminescent hybrid materials.

Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as an indispensable solid-state light source for the next generation lighting industry and display systems due to their unique properties including but not limited to energy savings, environment-friendliness, small volume, and long persistence. Until now, major challenges in pc-WLEDs have been to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. A comprehensive understanding of the nature and limitations of phosphors and the factors dominating the general trends in pc-WLEDs is of fundamental importance for advancing technological applications. This report aims to provide the most recent advances in the synthesis and application of phosphors for pc-WLEDs with emphasis specifically on: (a) principles to tune the excitation and emission spectra of phosphors: prediction according to crystal field theory, and structural chemistry characteristics (e.g. covalence of chemical bonds, electronegativity, and polarization effects of element); (b) pc-WLEDs with phosphors excited by blue-LED chips: phosphor characteristics, structure, and activated ions (i.e. Ce 3+ and Eu 2+ ), including YAG:Ce, other garnets, non-garnets, sulfides, and (oxy)nitrides; (c) pc-WLEDs with phosphors excited by near ultraviolet LED chips: single-phased white-emitting phosphors (e.g. Eu 2+ –Mn 2+ activated phosphors), red-green-blue phosphors, energy transfer, and mechanisms involved; and (d) new clues for designing novel high-performance phosphors for pc-WLEDs based on available LED chips. Emphasis shall also be placed on the relationships among crystal structure, luminescence properties, and device performances. In addition, applications, challenges and future advances of pc-WLEDs will be discussed.

Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties

The appropriate interfacial contact of heterojunction photocatalysts plays a critical role in transfer/separation of interfacial charge carriers. Design of two-dimensional (2D)/2D surface-to-surface heterojunction is an effective method for improving photocatalytic activity since greater contact area can enhance interfacial charge transfer rate. Herein, ultrathin 2D/2D WO3/g-C3N4 step-like composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultrathin tungsten trioxide (WO3) and graphitic carbon nitride (g-C3N4) nanosheets. The ultrathin WO3 and g-C3N4 nanosheets were obtained by electrostatic-assisted ultrasonic exfoliation of bulk WO3 and a two-step thermal-etching of bulk g-C3N4, respectively. The thickness of ultrathin WO3 and g-C3N4 nanosheets are 2.5–3.5 nm, which is equivalent to 5–8 atomic or molecular layer thickness. This ultrathin layered heterojunction structure can enhance surface photocatalytic rate because photogenerated electrons and holes at heterogeneous interface more easily transfer to surface of photocatalysts. Therefore, the obtained ultrathin 2D/2D WO3/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts exhibited better H2-production activity than pure g-C3N4 and WO3 with the same loading amount of Pt as cocatalyst. The mechanism and driving force of charge transfer and separation in S-scheme heterojunction photocatalysts are investigated and discussed. This investigation will provide new insight about designing and constructing novel S-scheme heterojunction photocatalysts.

Ultrathin 2D/2D WO3/g-C3N4 step-scheme H2-production photocatalyst

Synthesis, Luminescent Properties, and Biomedical Applications Shili Gai,†,‡ Chunxia Li,† Piaoping Yang,*,‡ and Jun Lin*,† †State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China ‡Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin, 150001, P. R. China

Recent Progress in Rare Earth Micro/Nanocrystals: Soft Chemical Synthesis, Luminescent Properties, and Biomedical Applications

A simple hydrothermal method has been developed for the systematic synthesis of lanthanide orthophosphate crystals with different crystalline phases and morphologies. It has been shown that pure LnPO4 compounds change structure with decreasing Ln ionic radius:  i.e., the orthophosphates from Ho to Lu as well as Y exist only in the tetragonal zircon (xenotime) structure, while the orthophosphates from La to Dy exist in the hexagonal structure under hydrothermal treatment. The obtained hexagonal structured lanthanide orthophosphate LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) products have a wirelike morphology. In contrast, tetragonal LnPO4 (Ln = Ho, Er, Tm, Yb, Lu, Y) samples prepared under the same experimental conditions consist of nanoparticles. The obtained hexagonal LnPO4 (Ln = La → Tb) can convert to the monoclinic monazite structured products, and their morphologies remained the same after calcination at 900 °C in air (Hexagonal DyPO4 is an exceptional case, it transformed to tetragonal DyPO...

Systematic synthesis and characterization of single-crystal lanthanide orthophosphate nanowires.

Rare-earth ion (Eu3+, Tb3+, Ce3+)-doped LaPO4 nanocrystalline thin films and their patterning were fabricated by a Pechini sol–gel process combined with soft lithography on silicon and silica glass substrates. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM), scanning electron microcopy (SEM), optical microscopy, absorption and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicate that the films begin to crystallize at 700 °C and the crystallinity increases with increasing annealing temperature. The morphology of the thin film depends on the annealing temperature and the number of coating layers. The 1000 °C annealed single layer film is transparent to the naked eye, uniform and crack-free with a thickness of about 200 nm and an average grain size of 100 nm. Patterned thin films with different strip widths (5–50 µm) were obtained by micromolding in capillaries (soft lithography). The doped rare earth ions show their characteristic emission in the nanocrystalline LaPO4 films, i.e., Eu3+5D0–7FJ
(J
= 1, 2, 3, 4), Tb3+5D3,4–7FJ
(J
= 6, 5, 4, 3, 2) and Ce3+ 5d–4f transition emissions, respectively. Both the lifetimes and the PL intensities of Eu3+ and Tb3+ increase with increasing annealing temperature, and the optimum concentrations for them were determined to be 5 mol% and 16 mol% of La3+ in LaPO4 thin films, respectively. An energy transfer phenomenon from Ce3+ to Tb3+ has been observed in LaPO4 nanocrystalline thin films, and the energy transfer efficiency depends on the doping concentration of Tb3+ if the concentration of Ce3+ is fixed.

Sol–gel synthesis and photoluminescent properties of LaPO4:A (A = Eu3+, Ce3+, Tb3+) nanocrystalline thin films

A fullerene derivative, 9-(1-(6-(3,5-bis(hydroxymethyl)phenoxy)-1-hexyl)-1H-1,2,3-triazol-4-yl)-1-nonyl [60]fullerenoacetate (C9), is employed to anchor the surface of a SnO2 electron transport layer (ETL) in planar heterojunction perovskite solar cells (PSCs). C9 suppresses charge recombination due to efficient passivation of oxygen-vacancy-related defects on the surface of the SnO2 ETL through the formation of a Lewis adduct between the under-coordinated Sn in SnO2 and hydroxyl terminal groups in C9. The C9 modifying layer enhances the extraction of photogenerated charge carriers due to the negligible injection barrier and strong electron affinity. C9 can also improve the quality of the perovskite film with enlarged grain size, reduced grain boundary and improved crystallinity. The PSCs based on C9-modified SnO2 exhibit improved photovoltaic performance with efficiency up to 21.3% with negligible hysteresis, which is superior to the control devices based on bare SnO2 (20.0%). Moreover, the ambient, photo and electric-field stability of the modified devices is also enhanced.

Fullerene derivative anchored SnO2 for high-performance perovskite solar cells

Self‐Adhesive Macroporous Carbon Electrodes for Efficient and Stable Perovskite Solar Cells

A TiO2/ZnO electron transport bilayer, which combines the advantages of high electron extraction and low interfacial recombination together, has been designed for planar perovskite solar cells. With this bilayer, the front surface recombination in the cell is significantly suppressed, and a high efficiency exceeding 17% has been achieved. These results suggest a promising and simple approach to further design photovoltaic devices from the aspect of charge transport and recombination.

Huiyin Zhang

Papers

Sol–gel synthesis and photoluminescent properties of LaPO4:A (A = Eu3+, Ce3+, Tb3+) nanocrystalline thin films

Fullerene derivative anchored SnO2 for high-performance perovskite solar cells

Self‐Adhesive Macroporous Carbon Electrodes for Efficient and Stable Perovskite Solar Cells

Highly efficient planar perovskite solar cells with a TiO2/ZnO electron transport bilayer

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis