Interpretation of europium(III) spectra

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

White light-emitting diodes (WLEDs) as new solid-state light sources have a greatly promising application in the field of lighting and display. So far much effort has been devoted to exploring novel luminescent materials for WLEDs. Currently the major challenges in WLEDs are 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. In recent years, numerous efforts have been made to develop single-phase white-light-emitting phosphors for near-ultraviolet or ultraviolet excitation to solve the above challenges with certain achievements. This review article highlights the current methods to realize the white light emission in a single-phase host, including: (1) doping a single rare earth ion (Eu3+, Eu2+ or Dy3+) into appropriate single-phase hosts; (2) co-doping various luminescent ions with different emissions into a single matrix simultaneously, such as Tm3+/Tb3+/Eu3+, Tm3+/Dy3+, Yb3+/Er3+/Tm3+etc.; (3) codoping different ions in one host to control emission color via energy transfer processes; and (4) controlling the concentration of the defect and reaction conditions of defect-related luminescent materials.

How to produce white light in a single-phase host?

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

This paper reflects the achievements and the challenges ahead in the field of organic light emitting diodes (OLEDs). The primary intention of this paper is to study different organic materials synthesized so far and the OLEDs fabricated for solid-state lighting. After deep review of literature we have synthesized and characterized rare earth based europium organic complexes Eu(TTA)3Phen, Eu(x)Y(1−x)(TTA)3Phen, and Eu(x)Tb(1−x)(TTA)3Phen, where x = 0.4 and 0.5 by solution technique maintaining stoichiometric ratio. Blended films of pure and doped Eu complexes that are molecularly doped into polymer resins namely polymethylmethacrylate (PMMA) and polystyrene (PS) are prepared according to weight percentage. Concentration effect on absorption and emission spectra of the blended films was studied for different weight percentages (10, 25, 50, 60%). All the complexes doped in PMMA showed an excellent transparency of 90–97% while the complexes doped in polystyrene showed a transparency of 85–90%, bit less than in PMMA. Energy gap of the synthesized complexes have been determined in PMMA and PS. Considering the facts that these complexes have good solubility in most of the organic solvents, the absorption spectra of Eu(TTA)3Phen, Eu0.5Y0.5(TTA)3Phen and Eu0.5Tb0.5(TTA)3Phen complexes are studied, and OLED devices having the structure ITO/m-MTDATA/α-NPD/TPBi:Eu(x)Y(1−x)(TTA)3Phen/Alq3/LiF:Al (where x = 0.4, 0.5) were fabricated and characterized. Significant red emission was observed from fabricated OLED devices at 612 nm when operated in a range of 10–18 V. Thus the synthesized rare earth based organic complexes are the best suitable candidates for fabrication of red OLED devices. The extensive review on OLEDS concludes that our present lighting system can be replaced with white OLEDS, recently developed energy saving lighting technology.

Organic light emitting diodes: Energy saving lighting technology—A review

A deep red phosphor Li2MgTiO4:Mn4+ exhibiting abnormal emission: Potential application as color converter for warm w-LEDs

A spatial/temporal dual-mode optical thermometry platform based on synergetic luminescence of Ti4+-Eu3+ embedded flexible 3D micro-rod arrays: High-sensitive temperature sensing and multi-dimensional high-level secure anti-counterfeiting

Here we report a series of multifunctional Cr3+-doped magnesium gallogermanate particles Several minutes of ultraviolet (UV) light excitation can lead to strong near-infrared (NIR) long persistent luminescence (LPL) at 600–850 nm with a long lasting time of at least 25 h After the disappearance of LPL, NIR photostimulated persistent luminescence (PSPL) can be rejuvenated repeatedly several times by an external photostimulus (visible or NIR light) Meanwhile, the material shows photochromic (PC) properties, ie, the surface color can change reversibly between white/pale green and rosybrown with high fatigue resistance by alternating UV and visible light irradiation When the temperature is increased to 300 °C, the induced rosybrown surface color can also be bleached This new multifunctional material has potential applications in a wide range of fields, such as in vivo bio-imaging, optical information write-in and read-out media, erasable optical memory media and optical sensors The continuous trap distribution and modulation were characterized The optimum trap depth was determined to be 051–086 eV In addition, we gained insight into the mechanism of multifunctional properties and the interconnection between them

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20 particles with long persistent and photostimulated persistent luminescence, and photochromic properties

Here, we report a novel long-persistent luminescence (LPL) phosphor, Ba2SiO4:Eu2+,Ho3+. The crystal structure, photoluminescence, photoluminescence excitation and LPL decay behaviors were studied systematically. The developed LPL phosphor Ba2SiO4:Eu2+,Ho3+ shows super-LPL, which remains above 2.97 mcd m−2 even 24 h after the removal of UV irradiation source. The outstanding LPL performance is mainly derived from the tailoring of trap distribution via Ho3+ co-doping. 15 days after UV irradiation, the sample still shows observable green luminescence by 980 nm stimulation. By means of photostimulated luminescence (PSL), excitation duration, decay duration and excitation temperature dependent thermoluminescence spectra, the continuous trap distribution, trap distribution modulation and dynamics of electron motion are characterized. The role of co-dopant Ho3+ serving as electron traps and the tailoring of trap distribution are revealed. The fabrication of Ba2SiO4:Eu2+,Ho3+ phosphor film allows optical information write-in after passing UV light through a photomask (projection printing method) and then the stored information is read out by thermal stimulation or 980 nm photostimulation, which holds great promise for optical information storage. Moreover, combined with the experimental and DFT calculation results, a tentative schematic diagram is proposed for the illustration of LPL and PSL mechanism in Ba2SiO4:Eu2+,Ho3+.

Trap distribution tailoring guided design of super-long-persistent phosphor Ba2SiO4:Eu2+,Ho3+ and photostimulable luminescence for optical information storage

A dual-emission (UV/Visible) phosphor SrZrO3: Pr3+ was prepared by a high-temperature solid-state reaction method The afterglow including ultraviolet (UV) and visible region which originated from self-trapped excitons and f–f transitions in Pr3+ was first observed after the short UV-irradiation All as-prepared phosphors were studied systematically by X-ray diffraction, photoluminescence (PL) spectra, decay curves, long afterglow spectra (LAG), and thermoluminescence (TL) glow curves The PL intensity and the performance of afterglow are dependent on the concentration of Pr3+ ions The optimal concentration of Pr3+ ions for the brightest PL emission and the best afterglow characteristic were experimentally to be 05% and 04%, respectively The different mechanisms for concentration quenching in both cases were discussed A model was proposed on the basis of experimental results to discuss the mechanism of LAG in SrZrO3: Pr3+ in detail

Guifang Ju

Papers

A deep red phosphor Li2MgTiO4:Mn4+ exhibiting abnormal emission: Potential application as color converter for warm w-LEDs

A spatial/temporal dual-mode optical thermometry platform based on synergetic luminescence of Ti4+-Eu3+ embedded flexible 3D micro-rod arrays: High-sensitive temperature sensing and multi-dimensional high-level secure anti-counterfeiting

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20 particles with long persistent and photostimulated persistent luminescence, and photochromic properties

Trap distribution tailoring guided design of super-long-persistent phosphor Ba2SiO4:Eu2+,Ho3+ and photostimulable luminescence for optical information storage

Luminescence Properties of Dual‐Emission (UV/Visible) Long Afterglow Phosphor SrZrO3: Pr3+