Luminescence and Defect Properties of Novel Bluish-Green Phosphor β-Zn3(PO4)2∶Zr4+

Luminescence and defect properties of novel phosphor β-Zn3(PO4)2:Zr4 were systematically investigated. Corresponding to its lowest optical absorption transition at 240 nm, phosphor emits a bluish-green light at 485 nm, which yields the Stokes shift about 20000 cm-1. The unusual optical properties of Zr4 ion are ascribed to its uncommon coordination environment. In addition it shows intensive bluish-green long lasting phosphorescence(LLP) due to the existence of electron trap, which is generated by aliovalent substitution of Zr4 ion for the cation site in the matrix as shown in thermoluminescence(TL) spectrum.     

Layer-by-layer assembly of long-afterglow self-supporting thin films with dual-stimuli-responsive phosphorescence and antiforgery applications

The assembly of thin films (TFs) having long-lasting luminescence can be expected to play an important role in the development of new-generation smart sensors,anti-counterfeiting materials,and information-encryption systems.However,such films are limited compared with their powder and solution counterparts.In this study,by exploiting the self-organization of phosphors in the two-dimensional (2D) galleries between clay nanosheets,we developed a method for the ordered assembly of long-afterglow TFs by utilizing a hydrogen-bonding layer-by-layer (LBL) process.Compared with the pristine powder,the TFs exhibit high polarization and up-conversion room-temperature phosphorescence (RTP),as well as enhanced quantum yields and luminescence lifetimes,allowing them to be used as room-temperature phosphorescent sensors for humidity and oxygen.Moreover,modified day-based hybrids with multicolor RTP can serve as anti-counterfeiting marks and triple-mode 2D barcode displays.We anticipate that the LBL assembly process can be extended to the fabrication of other inorganic-organic room-temperature phosphorescent hybrids with smart luminescent sensor and antiforgery applications.     

A comparison of local phosphorescence detection and fluid dynamic gauging methods for studying the removal of cohesive fouling layers: Effect of layer roughness

The performance of industrial cleaning in place (CIP) procedures is critically important for food manufacture. CIP has yet to be optimised for many processes, in part since the mechanisms involved in cleaning are not fully understood. Laboratory tests have an important role in guiding industrial trials, and this paper introduces and compares two experimental techniques developed for studying CIP mechanisms: local phosphorescence detection (LPD), and scanning fluid dynamic gauging (sFDG).To illustrate the comparison, each technique is used to investigate the influence of soil topology on the cleaning of pre-gelatinised starch-based layers from stainless steel (SS 316) substrates by aqueous NaOH solutions at ambient temperature. The roughness of the soil surface is varied by incorporating zinc sulphide particles with different particle size distributions (range 1–80 μm) into the starch suspensions. The soil roughness increased with the use of larger particles, increasing the 3D arithmetic mean roughness (S_a) of the dry layers (range 0.37–3.33 μm). Rough layers were cleaned more readily than those containing small inclusions, with a good correlation between the cleaning rates observed during LPD and FDG measurements. The LPD technique, which is an instrumented CIP test, gives a better indication of the cleaning time, while sFDG measurements provide further insight into the removal mechanisms.     

Photoluminescence properties of Eu-activated BaCa2Al8O15 nanophosphors

A new blue-emitting nanophosphor of Eu²⁺-activated BaCa₂Al₈O₁₅ was synthesized by the Pechini method. The phosphors were investigated by X-ray powder diffraction (XRD) measurement and confirmed to be a pure crystalline phase of BaCa₂Al₈O₁₅. The photoluminescence excitation and emission spectra, the luminescence decay and the color coordinates were taken to investigate the luminescence characteristics. The dependence of luminescence intensities BaCa₂Al₈O₁₅:Eu²⁺ on the doping concentrations was investigated. This nanophosphor can be efficiently excited by UV light and presents bright blue luminescence. Under the same conditions, the light yield of BaCa₂Al₈O₁₅:Eu²⁺ is about 1.2 times higher than that of blue-emitting phosphor BaMgAl₁₀O₁₇:Eu²⁺. Eu²⁺-activated BaCa₂Al₈O₁₅ nanophosphor exhibits the long-lasting phosphorescence, which was analyzed by measuring the afterglow decay curves. The co-doped Eu³⁺ ions and some defects were suggested to be the possible trap-centers.     

Reduction-oxidation photocycle dynamics of flavins in starch films

The blue-light photo-reduction (conversion of oxidized flavin quinone via flavin semiquinone to fully reduced flavin hydroquinone) and dark re-oxidation of the flavins riboflavin and lumiflavin in starch (α-amylose) films was studied by absorption and luminescence spectroscopy. Blue-light photo-excitation caused an absorption, fluorescence, and phosphorescence decrease which recovered in the dark. The photo-reduction dark-oxidation cycle could be repeated. The efficiency of photo-reduction decreased with exposed excitation energy, and the speed of re-oxidation in the dark slowed down with time after excitation. The absorption did not fully recover. The fluorescence efficiency after a long time of storage in the dark increased beyond the initial flavin quinone fluorescence efficiency. Flavin photo-excitation is thought to cause starch-flavin restructuring (static fluorescence quenching center formation), enabling enhanced photo-induced starch to flavin electron transfer with subsequent flavin reduction and starch oxidation. In the dark, after light switch-off, thermal reversion of flavin reduction and starch oxidation occurred.     

New host materials based on fluorene and benzimidazole units for efficient solution-processed green phosphorescent OLEDs

New green host materials 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole and 1-(9,9′-spirobifluorene-2-yl)-2-phenyl-1H-benzimidazole for solution-processed green phosphorescent organic light-emitting devices have been designed and synthesized by attaching the electron transporting benzimidazole units to the rigid fluorene units. Owing to the non-planar structures, which decrease the π conjugation length of fluorene and benzimidazole rings, these fluorene derived derivatives show high triplet energy. The high triplet energy of newly host materials ensures efficient energy transfer from the host to the triplet emitter tris(2-phenylpyridine)iridium. Furthermore, the thermal, photophysical, electrochemical properties and crystal structures of 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole and 1-(9,9′-spirobifluorene-2-yl)-2-phenyl-1H-benzimidazole were investigated. The solution-processed single-layer green device using 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole as the host for the phosphorescence emitter tris(2-phenylpyridine)iridium showed the maximum luminance efficiencies of 10.1 cd/A. This result demonstrated that the newly synthesized, fluorene-based rigid host materials are advantageous for fabrication of highly efficient green phosphorescent organic light-emitting diodes.     

A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl‐Substituted Fluorene Units for Highly Efficient Blue Electrophosphorescence

Highly efficient blue electrophosphorescent organic light‐emitting diodes incorporating a bipolar host, 2,7‐bis(diphenylphosphoryl)‐9‐[4‐(N,N‐diphenylamino)phenyl]‐9‐phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6‐difluoro‐phenyl)pyridinato‐N,C^2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron‐donating (p‐type) triphenylamine group and an electron‐accepting (n‐type) 2,7‐bis(diphenyl‐phosphoryl)fluorene segment linked through the sp³‐hybridized C9 position of the fluorene unit. The lack of conjugation between these p‐ and n‐type groups endows POAPF with a triplet energy gap (E_T) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue‐emitting guest. In addition, the built‐in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF‐based device doped with 7 wt% FIrpic exhibits a very low turn‐on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W^?1). Even at the practical brightnesses of 100 and 1000 cd m^?2, the efficiencies remain high (20.2%/33.8 lm W^?1 and 18.8%/24.3 lm W^?1, respectively), making POAPF a promising material for use in low‐power‐consumption devices for next‐generation flat‐panel displays and light sources.     

meta-Linked spirobifluorene/phosphine oxide hybrids as host materials for deep blue phosphorescent organic light-emitting diodes

This study investigated the use of a novel modification in molecular design to get two new electron-transport host materials, SF3PO and BSF3PO. By linking the phosphine oxide moieties at meta-position of spirobifluorene rings, higher triplet energies could be easily achieved for these two new materials. The steric spirobifluorene structures could guarantee their good thermal stabilities. According to these properties, their applications as host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were explored. As expected, the deep blue emitting devices with Ir-complex FIr6 as phosphorescent dopants and SF3PO and BSF3PO as hosts had been fabricated and showed high efficiency of 28.5 and 22.0 cd/A, respectively, which were significantly higher than that of the para-linked analogue SPPO1.     

Synthesis, Characterization and Luminescence Properties of Rare Earth Complexes with Bis （Pyridinyl-Amide）

A ligand, N^1, N^4-di （ pyridin-2-yl ） succi- namide （L） and its lanthanide（ IH ） complexes （RE = La, Eu, Tb, Gd, Yb ） were synthesized and characterized in detail. The results indicate that the composition of the binary complexes is determined as [ REL （H2O）2（NO3）2] NO3, that the complexes are 1 ： 1 electrolytes in DMF, and that the Tb^3＋ complex has brightly green fluorescence in a solid state. At the same time, the energy levels of the excited triplet states for the six ligands were determined to be 22989 -1 cm . The fact that the ligand sensitize Tb^3＋ complexes was explained by the relative energy gap between the lowest triplet energy level of the ligand （T） and ^5Dj of Tb^3＋ or Eu^3＋ . When 2000 cm^-1 〈 △E（T-^5D4） 〈 3000 cm^-1, the luminescent intensity of the Tb^3＋ complex is stronger. When 3000 cm^-1〈 △E （T-^5D1）, the luminescent intensity of the Eu^3＋ complex is weak- er or close to nil. This means that the triplet energy level of the ligand is a chief factor that dominates RE^3＋ luminescence.