Ultrahigh-Energy-Transfer Efficiency and Efficient Mn2+ Red Emission Realized by Structural Confinement in Ca9LiMn(PO4)7:Eu2+,Tb3+ Phosphor.

Structural confinement on Eu2+-Mn2+ optical centers is an effective strategy to boost Mn2+ red emission. On the basis of the Ca9LiMn(PO4)7 (CLMP) host with a compact Eu2+-Mn2+ distance of ∼3.5 Å, a pure and intense Mn2+ red emission without seeing Eu2+ emission is realized, indicating that an ultrahigh energy transfer (ET) could be induced by a structural confinement effect. It is found that the Mn2+ emission intensity and quantum efficiency could be further improved by a Tb3+ bridging effect, which offers extra energy levels to reduce the energetic mismatch between the excited states of Eu2+ and Mn2+. The optimal sample CLMP:0.02Eu2+,0.90Tb3+ shows a promising performance in terms of high color purity (93.9%), high quantum efficiency (QE = 51.2%), and good thermal stability (70% of the room-temperature value at 373 K). All of the results demonstrate that CLMP:Eu2+,Tb3+ phosphor is a promising red-light-emitting-diode phosphor, and the structural confinement effect should be developed as a general strategy to enhance the ET efficiency for a pure and efficient emission.

Bright solid-state luminescence of green-red tunable CdTe@BaCO3 composite: Synthesis and properties.

Realizing efficient solid-state luminescence is of great important to expand quantum dots (QDs) application fields. This work reports the preparation of CdTe@BaCO3 composite by a one-pot precipitation method. Both steady-state PL and PL decay characteristics in either solid-state or colloid solution show no obvious difference, mainly benefited from the effective protection of BaCO3 on QDs from the external environment. By utilizing green and red CdTe QDs as dual-color emission centers, precise emitting-color control from green (0.312, 0.667) to red (0.691, 0.292) could be achieved in CdTe@BaCO3 composite by adjusting volume ratio of CdTe solution precursor. Our results demonstrate that this composite material shows bright solid-state luminescence and facile adjustment of the emitting color in QDs-based composite is feasible, which could offer new path to design color-tunable luminescent materials for future optoelectronic applications.

High-efficient and pH-sensitive orange luminescence from silicon-doped carbon dots for information encryption and bio-imaging.

The exploration of carbon dots (CDs) with high quantum yield, facile synthesis path and satisfying output for their multiple applications remains a challenge. Thus, a silicon-doped orange-emitting carbon dots (O-CDs) is synthesized via a one-step hydrothermal method o-phenylenediamine and ethyl orthosilicate as raw materials. The O-CDs exhibits a bright and non-excitation-dependent emission peaking at 580 nm, and the corresponding quantum yield could be greatly boosted from 39.2 % to 64.1 % by silicon doping. The obtained O-CDs possess good biocompatibility and promising luminescence stability with varying solvents, ionic concentrations and temperatures. Its bio-imaging ability is performed by incubating zebrafish embryos with O-CDs aqueous solution, and clear in-vivo fluorescent images are obtained. Furthermore, due to its high-efficient and specific pH-sensitive emission with excellent dispersibility, the O-CDs can be used as a fluorescent ink for dual-model data encry/decryption in both hand-writing and stamp printing. Therefore, the as-prepared O-CDs show the potential as promising candidate for biomedical diagnosis, data encryption, and anti-counterfeiting.

Pb(II) detection and versatile bio-imaging of green-emitting carbon dots with excellent stability and bright fluorescence.

Green-emitting carbon dots (G-CDs) were synthesized via a simple and green hydrothermal method using betaine hydrochloride and sulfadiazine as carbon and nitrogen sources, respectively. Excellent luminescence stability with varying pH, salt concentrations, temperature is found with excitation-independent emission. G-CDs can be successfully used for the detection of Pb(ii) in the range of 0-200 µM. There was good linear relationship between the Pb(ii) concentration and G-CD fluorescence intensity with a correlation coefficient of 0.993, and the limit of detection (LOD) was 3.0174 µmol L-1. Due to its good biocompatibility, G-CDs can be successfully applied to zebrafish imaging as well as cell imaging, and the results show that G-CDs is more suitable for the zebrafish embryo imaging. Our results suggested that the obtained G-CDs can be used as multifunctional probes, highlighting their potential in different biological studies.

Tunable photoluminescence and energy transfer of Sr9LiMg(PO4)7: Ce3+/Tb3+/Mn2+ phosphors.

The Ce3+/Tb3+/Mn2+ activated color-tunable phosphors Sr9LiMg(PO4)7 (SLMP) were prepared by solid-state reaction with post-annealing treatment. The structural, static and time-resolved luminescent properties are studied in detail. XRD pattern showed the pure trigonal phase of Sr9LiMg(PO4)7 at an annealing temperature of 1300 °C. Ce3+-doped SLMP phosphor exhibits near-ultraviolet emission with peak-wavelength at 380 nm. Efficient Ce3+-Tb3+/Mn2+ energy transfer process is demonstrated by luminescence spectrum and luminescence lifetimes of as-prepared samples. The emitting-color of SLMP: Ce3+/Tb3+/Mn2+ was tunable through changing Ce3+/Tb3+/Mn2+ ratio. Emission peak intensity of SLMP: Ce3+, Tb3+ phosphor shows good thermal stability with rising temperature. These results suggest its great potential as luminescent materials with good performance for UV-excitable applications.

A high-sensitive ratiometric luminescent thermometer based on dual-emission of carbon dots/Rhodamine B nanocomposite.

A core-shell nanocomposite based on carbon dots (CD)/Rhodamine B (RhB) is realized by a facile method. The composite particles show spherical shape with narrow size distribution, non-agglomeration and smooth surface. The as-obtained nanocomposite shows the characteristic dual-emission of thermal-stable CD blue emission and thermal-sensitive RhB red emission at a single excitation wavelength. The fluorescence intensity ratio (FIR) is found to have a good linear relationship (R2 > 0.993) with temperature, while the corresponding maximum absolute and relative sensitivity is 2.01% K-1 and 1.39% K-1 in range of 283-373 K. The research provides a simple approach to create novel dual-emitting nanocomposites for temperature sensing application in micron-scale and biological field.