Green Afterglow Research Articles

Luminescence properties of silk cocoon derived carbonaceous fluorescent nanoparticles/PVA hybrid film

Carbonaceous fluorescent nanoparticles (CFNs) with broad particle distribution were synthesized by thermal-treatment using carbonation of silk cocoon as raw materials. The experimental results showed tunable emission wavelength of the nanoparticles. The quantum yield of the CFNs was calculated to be 23%. A CFNs/PVA hybrid thin film was prepared from a blend of the CFNs with polyvinyl alcohol (PVA) showing interesting green afterglow which could be observed by naked eyes. The afterglow spectrum revealed that the CFNs/PVA thin film had a broad afterglow emission peak located at 520nm. The afterglow intensity decay curve of the film showed visually recognizable period longer than 140s. The PVA–PVA hydrogen bonding in the PVA matrix may play a key role for the afterglow.

Influence on Afterglow Spectra due to Different Phases of Zn<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>: Mn<sup>2+</sup>

High temperature solid state reaction has been used to prepare Zn3(PO4)2: Mn2+. XRD analysis shows that different phases have been generated with different Mn2+ doping concentration at the same sintering temperature. Low Mn2+ doping concentration is conducive to form α phase, while γ is in favor of high Mn2+ doping concentration. In α phase, the emission spectrum of Mn2+ is a wide emission band peaking at 542 nm, green fluorescence. In γ phase, the emission spectrum of Mn2+ is a wide emission band peaking at 608 nm, red fluorescence. In the both phases, green and red afterglows have been observed. The red afterglow in γ phase has stronger initial brightness and longer afterglow decay time than the green afterglow in α phase, the reason of which lies in the larger trap concentration in γ phase.

Characterization of afterglow-related spectroscopic effects in vacuum sintered Tb3+, Sr2+ co-doped Lu2O3 ceramics

Persistent luminescence phosphors, Tb3+, Sr2+ co-doped Lu2O3 ceramics were fabricated under vacuum at 1870°C. A strong green color afterglow could be observed after excitation with 254nm UV radiation. The afterglow was found to be roughly doubled in intensity upon stimulation with violet or blue-green photons (∼400–600nm) as well as upon IR radiation (∼800–980nm). Hence, the enhancement of the green afterglow could also be attained by means of natural sunlight. Short wavelength UV radiation was found to induce an extrinsic absorption band below about 600nm and extending into the deep UV. This was mirrored by a simultaneous decrease of the absorption by Tb3+ around 230–320nm. The extrinsic absorption seemed to contain at least two overlapping components which supposedly resulted from a band related to Tb4+/Tb3+-h and a feature resulting from F/F+ centers created upon irradiation with short UV. This absorption was shown to be reversible, as it disappeared after a short heat treatment at about 300°C as well as with continuous irradiation of ∼400nm radiation.

PREPARATION OF PERSISTED LUMINESCENCE PIGMENT AND INVESTIGATION IN GLAZE COMPATIBILITY

In this paper, preparation of SrAl2O4:Eu,Dy luminescent pigment has been investigated. Coprecipitation as a low cost and facile method was selected. X-ray diffraction patterns indicated the formation of SrAl2O4:Eu,Dy phase through calcinations process above 800 °C. Moreover, a few amount of silica caused the structural transformation to alumina silicate phase. Transparent glaze which consist of a few amount of luminescent pigment was obtained at 600° C under different atmosphere conditions. The photoluminescence properties of luminescence glaze revealed that the firing atmosphere has vital effect on luminescence features of coating glaze. Although, the luminescence decay of glaze was completely eliminated in oxide atmosphere, but the green afterglow of obtained sample was remained in argon atmosphere.

The photoluminescence, afterglow and up conversion photostimulated luminescence of Eu 3+ doped Mg 2SnO 4 phosphors

The Mg 2SnO 4:Eu 3+ phosphor with reddish photoluminescence, green afterglow and photostimulated luminescence is obtained by the solid state method. The host related afterglow is greatly enhanced by doping of Eu 3+ and it can last nearly 6 h when the Eu 3+ concentration is 1 mol%. The photostimulated luminescence is found to be weakened by doping of Eu 3+. It was revealed that all the shallow traps and a part of the deep traps are involved in afterglow. The majority of deep traps are responsible for photostimulated luminescence. The impact of doping Eu 3+ on the afterglow and photostimulated luminescence is investigated and we propose a feasible interpretation.

Direct Preparation of Strontium Aluminate Phosphor Plate by Reactive Infiltration Method

Sr-aluminate phosphor plates were prepared by the infiltration-reaction method. The mixture of SrCO3, Eu2O3, Dy2O3 powders were mixed and coated on the porous alumina plate, followed by heating at 1300°C for 4h under 10%H2+90%N2 gas atmosphere. After processing, the surface part of the Al2O3 plate became dense, ∼20μm thickness. SrAl2O4 and Sr3Al2O6 phases were observed as the product. The coated mixture powder changed to a liquid state and infiltrated into the pores of the alumina plate. During processing, the following reactions occurred; SrCO3→SrO+CO2, SrO+Al2O3→SrAl2O4, 3SrO+Al2O3→Sr3Al2O6. According to the Sr distribution analysis at the dense layer, Sr3Al2O6 and SrAl2O4 phases were mainly formed in the surface-side and Al2O3-side layers, respectively. This plate emits green luminescence by the irradiation of the "black-light". The wave length of the emitted light was in the range of 450–650nm, and the maximum intensity appeared at 520nm. Also, this plate showed green afterglow. The best mixing ratio was Sr/Eu/Dy = 5/1/1. This afterglow intensity decreased from 0.14cdm−2 (0sec.) to 0.01cdm−2 (30sec.). We observed the green afterglow for 3 hours in the dark.

Effect of Ho Co-Doping on the Long Lasting Emission of CaGa2S4:Eu

To investigate the long-lasting green afterglow from Ho added CaGa2S4:Eu compounds, photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured as a function of Ho concentration by keeping Eu one at 0.1 and 0.5 mol %. As Ho concentration increases, PL intensity of Eu decreases. PL from Ho at 660 nm has an additional broad excitation band ranging from 400 to 500 nm, emerging only if Eu2+ ion is co-doped. Since this new band just coincides with the Eu2+ emission in energy, electrons excited to the 5d states of Eu2+ are considered to transfer to the Ho excited states, which are actually confirmed by the weakened Eu emission observed. In the decay curve of Eu emission in a co-doped sample, two long-lasting components are observed. Their lifetimes, however, steeply decrease when Ho concentration increases more than 1 mol %. In this paper, energy transfer between the two dopants is discussed.

Luminescence and long-lasting afterglow in Mn2+ and Eu3+ co-doped ZnO–GeO2 glasses and glass ceramics prepared by sol–gel method

To develop new fluorescent and afterglow materials, Mn2+ and Eu3+ co-doped ZnO–GeO2 glasses and glass ceramics were prepared by a sol–gel method and their optical properties were investigated by measuring luminescence, excitation and afterglow spectra, and luminescence quantum yield (QY). Under UV irradiation at 254 nm, some glasses and all of the glass ceramics showed green luminescence peaking at 534 nm due to the 4T1 → 6A1 transition of tetrahedrally coordinated Mn2+ ions. The strongest luminescence was observed in a glass ceramic of 0.1MnO–0.3Eu2O3–25ZnO–75GeO2 heat treated at 900 °C, with QY of 49.8%. All of the green-luminescent glasses and glass ceramics showed green afterglow, and the afterglow lasting for more than 60 min was obtained in a glass ceramic heat treated at 900 °C. It is considered that the Eu3+ ions may behave as electron trapping centers to be associated with the occurrence of the green afterglow due to the Mn2+ ions in the co-doped system.

Luminescence studies on SrMgAl 10O 17:Eu, Dy phosphor crystals

Using urea as fuel, SrMgAl 10O 17:Eu, Dy phosphor was prepared by a combustion method. Its luminescence properties under ultraviolet (UV) excitation were investigated. Pure SrMgAl 10O 17 phase was formed by urea-nitrate solution combustion synthesis at 550 °C. The results indicated that the emission spectra of SrMgAl 10O 17:Eu, Dy has one main peak at 460 nm and one shoulder peak near 516 nm, which are ascribed to two different types of luminescent Eu 2+ centers existing in the SrMgAl 10O 17 matrix crystal. The blue luminescence emission of SrMgAl 10O 17:Eu phosphors was improved under UV excitation by codoping Dy 3+ ions. The SrMgAl 10O 17:Eu phosphors showed green afterglow ( λ=516 nm) when Dy 3+ ions were doped. Dy 3+ ions not only successfully play the role of sensitizer for energy transfer in the system, but also act as trap levels and capture the free holes in the spinel blocks.

The trap states in the Sr 2MgSi 2O 7 and (Sr,Ca)MgSi 2O 7 long afterglow phosphor activated by Eu 2+ and Dy 3+

The excellent long afterglow phosphor Sr 2MgSi 2O 7:Eu 2+,Dy 3+ with the blue light and (Sr,Ca)MgSi 2O 7:Eu 2+,Dy 3+ emitting blue–green afterglow for more than 20 h under the UV excitation were prepared. The trap states in the samples are studied by thermoluminescence (TL) and photo-stimulated luminescence (PSL). The results of TL and PSL exhibit plenty of traps which are responsible for the long afterglow. TL study shows that a broad band appears at 330 and 357 K for (Sr,Ca)MgSi 2O 7:Eu 2+,Dy 3+ with the thermal depth of trap E TL = 0.66 eV and for Sr 2MgSi 2O 7:Eu 2+,Dy 3+ with the thermal depth of trap E TL = 0.75 eV, respectively. PSL spectra reveals that the trapped carries also can be released by optical stimulation with the E PSL = 1.56–1.94 eV. The relation between TL and PSL can be explained by the configuration coordinate mode.

Isotopic equilibration of nitrogen on potassium-promoted transition metal catalysts

Dy3+ doped barium aluminate (BaAl2O4:Dy3+) phosphors were prepared via the sol–gel combustion route at the ignition temperature of 600 °C. The phosphors were characterized with X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Regardless of the absence of Eu2+ luminescent centers, broadband blue–green afterglow with its peak at about 490 nm was recorded in the BaAl2O4:Dy3+ phosphors. The decay profile of the blue–green afterglow can be best fitted into a two-component exponential function with the two lifetime decay constants to be 8.81 and 45.25 s, respectively. The observation of blue–green afterglow from BaAl2O4:Dy3+ in the absence of Eu2+ provides unique opportunity in unveiling the afterglow mechanisms of rare-earth doped alkaline-metal aluminates. Possible mechanisms on the blue–green afterglow in BaAl2O4:Dy3+ phosphors are discussed in terms of the Dy3+ ions introduced trap centers as well as luminescent centers in the crystal lattice.