Bingkun Chen

Red emissive CuInS 2 -based nanocrystals: a potential phosphor for warm white light-emitting diodes

We here report the integration of red emissive CuInS(2) based nanocrysals as a potential red phosphor for warm light generation. By combining red emissive CuInS(2) based nanocrysals with commercial yellow emissive YAG:Ce and green emissive Eu(2+) doped silicate phosphors, we fabricated warm white light-emitting diodes with high color rendering index up to ~92, high luminous efficiency of 45~60 lm/W and color temperature less than 4000K.

Synthesis, optical properties and applications of light-emitting copper nanoclusters

Metal nanoclusters (NCs) containing a few to a few hundreds of atoms bridge the gap between nanoparticles and molecular compounds. The last decade evidenced impressive developments of noble metal NCs such as Au and Ag. Copper is an earth abundant, inexpensive metal from the same group of the periodic table, which is increasingly coming into focus for NC research. This review specifically addresses wet chemical synthesis methods, optical properties and some emerging applications of Cu NCs. As surface protecting templates/ligands play an important role in the stability and properties of Cu NCs, we classified the synthetic methods by the nature of the capping agents. The optical properties of Cu NCs are discussed from the point of view of the effects of the metal core, surface ligands and environment (solvents and aggregation) on the emission of the clusters. Applications of luminescent Cu NCs in biological imaging and light emitting devices are considered.

Pr3+-doped heavy metal germanium tellurite glasses for irradiative light source in minimally invasive photodynamic therapy surgery

Pr3+-doped medium-low phonon energy heavy metal germanium tellurite (NZPGT) glasses have been fabricated and the intense multi-peak red fluorescence emissions of Pr3+ are exhibited. Judd-Ofelt parameters Ω2 = 3.14 × 10(-20)cm(2), Ω4 = 10.67 × 10(-20)cm(2) and Ω6 = 3.95 × 10(-20)cm(2) indicate a high asymmetrical and covalent environment in the optical glasses. The spontaneous emission probabilities A(ij) corresponding to the 1D2→3H4, 3P0→3H6, and 3P0→3F2 transitions are derived to be 1859.6, 6270.1 and 17276.3s(-1), respectively, and the relevant stimulated emission cross-sections σ(em) are 5.20 × 10(-21), 14.14 × 10(-21) and 126.77 × 10(-21)cm(2), confirming that the effectiveness of the red luminescence in Pr3+-doped NZPGT glasses. Under the commercial blue LED excitation, the radiant flux and the quantum yield for the red fluorescence of Pr3+ are solved to be 219μW and 11.80%, respectively. 85.24% photons of the fluorescence in the visible region are demonstrated to be located in 600-720nm wavelength range, which matches the excitation band of the most photosensitizers (PS), holding great promise for photodynamic therapy (PDT) treatment and clinical trials.

Top‐Down Fabrication of Stable Methylammonium Lead Halide Perovskite Nanocrystals by Employing a Mixture of Ligands as Coordinating Solvents

A top-down method is demonstrated for the fabrication of CH3 NH3 PbBr3 and CH3 NH3 PbI3 perovskite nanocrystals, employing a mixture of ligands oleic acid and oleylamine as coordinating solvents. This approach avoids the use of any polar solvents, skips multiple reaction steps by employing a simple ultrasonic treatment of the perovskite precursors, and yields rather monodisperse blue-, green-, and red-emitting methylammonium lead halide nanocrystals with a high photoluminescence quantum yield (up to 72 % for the green-emitting nanocrystals) and remarkably improved stability. After discussing all relevant reaction parameters, the green-emitting CH3 NH3 PbBr3 nanocrystals are employed as a component of down-conversion white-light-emitting devices.

Highly transparent and colour-tunable composite films with increased quantum dot loading

Transparent films incorporated with quantum dots are promising light conversion materials for many cutting-edge technologies including light-emitting diodes and luminescent solar concentrators. In this work, we demonstrated that a combination of water soluble quantum dots and ultrathin cellulose nanofibers is an advantageous strategy to fabricate highly emissive thin films of tens of micrometers. By varying the composition of quantum dots, these thin films exhibit tunable photoluminescence emissions, ranging from blue to red as well as white light. Because of the inherent nanoscale phase separation of cellulose nanofibers, the loading content of quantum dots can be increased up to 50 wt%, which results in a significant increase of the refractive index. The combination of high refractive index (∼1.56), colour-tunable emissions (450–650 nm) and high transparency (∼80%, at a wavelength longer than the absorption band of quantum dots) makes them promising candidates for photonic and optoelectronic devices.

Reprecipitation synthesis of luminescent CH3NH3PbBr3/NaNO3 nanocomposites with enhanced stability

Stability is one of the most serious intrinsic limiting factors for the application of halide perovskites in optoelectronics. In this communication, we introduce the concept of space localization to tackle this problem by fixing the unstable organic methylamine cation using inorganic salts. The obtained luminescent CH3NH3PbBr3/NaNO3 nanocomposites exhibit enhanced stability against thermal and photo-degradations.

Mesoporous Aluminum Hydroxide Synthesized by a Single-Source Precursor-Decomposition Approach as a High-Quantum-Yield Blue Phosphor for UV-Pumped White-Light-Emitting Diodes

Strongly emissive (photoluminescence quantum yield up to 65%), thermally stable aluminum hydroxide blue phosphors are synthesized by a single-source precursor-decomposition approach. Blue-emitting UV-pumped light-emitting diodes (LEDs) based on the aluminum hydroxide phosphor reach luminous efficiency of 27.5 lm W-1 , while UV-white-LEDs integrating blue-emitting aluminum hydroxide and red-emitting CuInS2 nanocrystals achieve high color-rendering-index values of 94.3 and luminous efficiency of 23.5 lm W-1 .

Hexagonal Zn1−xCdxS (0.2 ≤ x ≤ 1) solid solution photocatalysts for H2 generation from water

A series of hexagonal Zn1−xCdxS photocatalysts with variable composition (0.2 ≤ x ≤ 1) is synthesized by a solvothermal method. XPS spectra of Zn 2p and Cd 3d regularly shift upon changing the composition of Zn1−xCdxS samples, due to the difference in the Mulliken atomic charges of Zn, Cd, and S. The photocatalytic activity of the samples for H2 evolution from water was tested under visible-light irradiation (λ ≥ 420 nm) without a cocatalyst; the Zn0.4Cd0.6S sample exhibited the highest photocatalytic H2 evolution rate, which was about 81 mL h−1 g−1. Under irradiation with a 368 nm LED, the H2 evolution rate decreased with increasing Cd fraction in the Zn1−xCdxS solid solution. By comparing the crystallinity, surface area, valence/conduction band positions, absorption spectra and fluorescence lifetimes, we conclude that the photocatalytic activity is related to the balance between the absolute positions of the valence/conduction bands and light absorption ability of the Zn1−xCdxS photocatalysts.

Broadband fluorescence emission of Eu 3+ doped germanotellurite glasses for fiber-based irradiation light sources

Eu3+ doped fiber-based germanotellurite (NZPGT) glasses with medium-low maximum phonon energy of 782 cm−1 have been fabricated and characterized. Judd-Ofelt intensity parameters Ω2 (6.25 × 10−20 cm2) and Ω4 (1.77 × 10−20 cm2) indicate a high asymmetrical and covalent environment around Eu3+ in the optical glasses. The spontaneous emission probability of the dominant transition 5D0→7F2 peaking at 612.5 nm and the corresponding maximum stimulated emission cross-section were derived to be 445.7 s−1 and 2.05 × 10−21 cm2, respectively, confirming the effectiveness of the red fluorescence emission. The quantum yield was derived to be 12% under 391 nm LED excitation, and approximately 88% photons have been demonstrated in wavelength range of 600−720 nm, indicating that Eu3+ doped NZPGT glasses under proper excitation conditions are promising optical materials for fiber-based irradiation light sources that are competent to activate diverse photodynamic therapy photosensitizers.

Yellow-light generation and engineering in zinc-doped cadmium sulfide nanobelts with low-threshold two-photon excitation

Through a simple doping route with zinc ion as a dopant in cadmium sulfide nanobelts, a bright yellow-colored light was obtained. The detailed chromaticity and brightness of the light can be engineered by the dopant concentration and the pumping power, which are used to control the dominant wavelength to any fine yellow color, and even cover the sodium-yellow-line of 589 nm. The nanobelts were synthesized through a chemical vapor deposition method. The peak shift of the XRD result proves that the zinc ions as a dopant exist in the nanobelts rather than in the ZnCdS alloy formation. Time-resolved photoluminescence of the nanobelt reveals the existence of the defect-related state, which induces a red band to further mix with green band-edge emission to form the yellow light. Moreover, low-threshold two-photon excitation was observed in the proper Zn-doped cadmium sulfide nanobelts. The dopant and pumping power-tuned generation and engineering of the yellow light makes it possible to use this kind of material as yellow light-emitting source.