Progress in discovery and structural design of color conversion phosphors for LEDs

Owing to the unique mechanism of photoelectron storage and release, long persistent phosphorescence, also called long persistent luminescence or long lasting afterglow/phosphorescence, plays a pivotal role in the areas of spectroscopy, photochemistry, photonics and materials science. In recent years, more research has focused on the manipulation of the morphology, operational wavebands and persistent duration of long persistent phosphors (LPPs). These desired achievements stimulated the growing interest in designing bio-labels, photocatalysts, optical sensors, detectors and photonic devices. In this review, we present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, materials system, and applications of LPPs. First, we introduce the recent developments in LPPs for the synthesis of nanoparticles from the aspects of particle sizes, monodispersity and homogeneity based on the urgent application of bio-imaging. In the later sections, we present the possible mechanisms, which involve the variation of trap distribution during the trapping and de-trapping process, complicated photo-ionization reaction of trap site levels and impurity centers together with their corresponding migration kinetics of carriers. Meanwhile, we emphasize the characterization techniques of defects, used to qualitatively or quantitatively describe the types, concentrations and depths of the traps. This review article also highlights the recent advances in suggested LPPs materials with a focus on the LPPs' hosts and optically active centers as well as their control, tuning and intrinsic links. We further discuss the classification of LPPs based on the different emission and excitation wavebands from the ultraviolet to the near-infrared region along with an overview of the activation mode of afterglow. Afterwards, we provide an exhibition of new products towards diverse application fields, including solar energy utilization, bio-imaging, diagnosis, and photocatalysts. Finally, we summarize the current achievements, discuss the problems and provide suggestions for potential future directions in the aforementioned parts.

Long persistent phosphors—from fundamentals to applications

Persistent luminescence instead of phosphorescence: History, mechanism, and perspective

Graphene-based heterojunction photocatalysts

To photo-catalytically degrade RhB dye using solar irradiation, CeO2 doped TiO2 nanocomposites were synthesized hydrothermally at 700 °C for 9 hrs. All emission spectra showed a prominent band centered at 442 nm that was attributed to oxygen related defects in the CeO2-TiO2 nanocrystals. Two sharp absorption bands at 1418 cm−1 and 3323 cm−1 were attributed to the deformation and stretching vibration, and bending vibration of the OH group of water physisorbed to TiO2, respectively. The photocatalytic activities of Ce-TiO2 nanocrystals were investigated through the degradation of RhB under UV and UV+ visible light over a period of 8 hrs. After 8 hrs, the most intense absorption peak at 579 nm disappeared under the highest photocatalytic activity and 99.89% of RhB degraded under solar irradiation. Visible light-activated TiO2 could be prepared from metal-ion incorporation, reduction of TiO2, non-metal doping or sensitizing of TiO2 using dyes. Studying the antibacterial activity of Ce-TiO2 nanocrystals against E. coli revealed significant activity when 10 μg was used, suggesting that it can be used as an antibacterial agent. Its effectiveness is likely related to its strong oxidation activity and superhydrophilicity. This study also discusses the mechanism of heterogeneous photocatalysis in the presence of TiO2.

https://cyberleninka.org/article/n/696250.pdf

Photodegradation of organic pollutants RhB dye using UV simulated sunlight on ceria based TiO2 nanomaterials for antibacterial applications.

Recent development in rare earth doped phosphors for white light emitting diodes

A variety of Eu3+-activated BaZrGe3O9 phosphors was synthesized via solid-state reaction. The phase formation of BaZrGe3O9:Eu3+ samples was verified by powder X-ray diffraction analysis, while Rietveld refinement method was used to confirm the crystal structure. The electronic structure and characteristic photoluminescence as well as cathodoluminescence properties were researched in detail. The samples show strong absorption at 394 nm, which matches well with the commercial near-ultraviolet chips. Under 394 nm excitation, the phosphors exhibit the characteristic emissions of Eu3+ ions consistent with the 5D0–7FJ transitions. Then we investigated the thermal stability detailedly. The temperature-dependent photoluminescence emission spectra suggest that the obtained phosphors have favorable thermal stability. A white light-emitting diode (WLED) lamp with low correlated color temperature and good color render index was fabricated with blue-emitting BaMgAl10O17:Eu2+, green-emitting Sr2SiO4:Eu2+ (commercial), ...

A Potential Red-Emitting Phosphor BaZrGe3O9:Eu3+ for WLED and FED Applications: Synthesis, Structure, and Luminescence Properties

High saturation magnetization of γ -Fe 2 O 3 nano-particles by a facile one-step synthesis approach

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High saturation magnetization of γ-Fe2O3 nano-particles by a facile one-step synthesis approach

Lead halide perovskite quantum dots (LHP QDs) exhibit great potential in the backlighting display of light-emitting diode applications. Light-emitting backlighting with high brightness, low cost, a...

Perovskite Quantum Dots for Application in High Color Gamut Backlighting Display of Light-Emitting Diodes

A novel blue-emitting phosphor Na3Sc2(PO4)3:Eu2+ was successfully synthesized by solid-state reaction. The crystal structure, bandgap, and photoluminescence properties were investigated in detail. Under n-UV excitation, the NSP:Eu2+ phosphor exhibits a narrow blue emission peaking at 458 nm with a FWHM of about 50 nm. The concentration quenching mechanism of the NSP:Eu2+ is dominated by the dipole–dipole interaction. Moreover, the NSP:Eu2+ shows better PL intensity, colour purity and thermal quenching properties compared to the commercial BAM phosphor. Non-equivalence replacement of Eu2+ ions for Na+ ions causing defects, inducing the abnormal thermal quenching behaviour. All these results suggest that the NSP:Eu2+ phosphor can be a potential candidate for n-UV LED applications.

Xicheng Wang

Papers

Recent development in rare earth doped phosphors for white light emitting diodes

A Potential Red-Emitting Phosphor BaZrGe3O9:Eu3+ for WLED and FED Applications: Synthesis, Structure, and Luminescence Properties

High saturation magnetization of γ-Fe2O3 nano-particles by a facile one-step synthesis approach

Perovskite Quantum Dots for Application in High Color Gamut Backlighting Display of Light-Emitting Diodes

Structure, photoluminescence and abnormal thermal quenching behavior of Eu2+-doped Na3Sc2(PO4)3: a novel blue-emitting phosphor for n-UV LEDs