Alkaline Earth Aluminates Research Articles

High color purity aluminate phosphor SryCa1-x-yAl12O19: xEu2+ for lighting and backlight display applications

In the context of the rapid advances in electronic information technology, the advancement of novel high-efficiency narrow-band blue phosphors represents a pivotal step in the advancement of high-quality liquid crystal displays (LCDs), as well as the development of white light-emitting diodes (WLEDs) with a reduced correlated color temperature (CCT). In this study, based on the sensitivity of Eu2+ emission to local environment, the alkaline earth aluminate material CaAl12O19 with high structural symmetry was selected as the matrix, and the symmetry of crystal structure was improved by replacing Ca2+ with Sr2+, the narrow-band emission of the phosphor is realized. The Sr0.9Ca0.09Al12O19: 0.01Eu2+ (SCAO: Eu2+) phosphor exhibited narrow-band emission with the full width at half maximum (FWHM) of 45.76 nm, and the colour purity of up to 95.46 %. Moreover, the internal quantum efficiency (IQE) of SCAO: Eu2+ has been demonstrated to reach 81.70 %. In addition, SCAO: Eu2+ phosphor, (Ba, Sr)2SiO4: Eu2+ phosphor, CaAlSiN3: Eu2+ phosphor, and 275 nm UVLED chips were combined to prepare white LED devices exhibiting a low color temperature (3733 K). The three-band LEDs of SCAO: Eu2+, β-Sialon: Eu2+ and K2SiF6: Mn4+ exhibited a colour gamut covering 84.75 % of the National Television Standards Committee (NTSC) standard. This indicates that the phosphor possesses the characteristics of a highly effective narrow-band blue-light-emitting substance with considerable potential for utilization in lighting and backlighting displays.

Structural and Luminescent Characteristics of Divalent Europium Activated Barium Aluminate with the Tridymite Structure Synthesized by the Sol-Gel Technique

Abstract: In this study, alkaline earth aluminates were investigated as potential hosts for new blue luminescent materials with nanoparticles. Ba1-xEuxAl2O4 with the stuffed tridymite hexagonal structure was successfully synthesized at 900 °C under controlled sol-gel conditions. Divalent europium was effectively used to activate this host material, producing a brilliant blue-emitting phosphor. Its spectral photoluminescence at 408 nm appears to be in a region close to the laser blue region, with chromaticity coordinate values suitable for the standard blue of the PAL TV system. Keywords: Blue phosphors, BaAl2O4, Divalent Europium (Eu2+), Sol-Gel synthesis, Critical energy transfer.

Preparation of polypropylene nanofibers reinforced multifunctional epoxy composite concrete with ultraviolet‐driven afterglow emission

AbstractIn order to develop smart concrete with afterglow emission, epoxy resin (EPX) was immobilized with nanoparticles of alkaline earth aluminate (NAEA) as a photoluminescent agent and electrospun polypropylene nanofibers (EPN) as a reinforcement agent. Scanning electron microscope images of EPN displayed diameters of 70–90 nm, whereas transmission electron microscopic images showed that NAEA has diameters of 3–9 nm. To create a transparent sheet that glows in the dark, NAEA were physically immobilized in EPN@EPX composite. CIE Lab and photoluminescence spectrum studies demonstrated that EPN@EPX bars turned greenish upon exposure to ultraviolet (UV) rays and greenish‐yellow in a darkened box. The luminous EPN@EPX morphologies and chemical compositions were analyzed using various analytical methods. The resistance to scratching of EPN@EPX bars was monitored to considerably increase with increasing NAEA concentration. The photoluminescence spectrum demonstrated two emission peaks at 437 and 518 nm. Photoluminescent EPN@EPX hybrids with low NAEA content have shown rapid photochromism reversibility. On the contrary, NAEA‐rich EPN@EPX bars displayed slow reversibility, glowing in the dark. Superhydrophobicity and UV blockage were found to be significantly improved in the luminescent colorless EPN@EPX hybrids.

Preparation of Lighting in the Dark and Photochromic Electrospun Glass Nanofiber-Reinforced Epoxy Nanocomposites Immobilized with Alkaline Earth Aluminates.

Alkaline earth aluminates (AEAs) as photoluminescent agents and silicon dioxide-based electrospun glass nanofibers with an average diameter of 150-450 nm as a roughening agent were prepared and applied to reinforce an epoxy resin toward the development of long-persistent photoluminescent and photochromic smart materials, such as smart windows and anticounterfeiting barcodes. With the physical immobilization of lanthanide-doped aluminate nanoparticles (NPs), a light-induced luminescent transparent glass@epoxy film was developed. The glass@epoxy samples were able to alter their color to green beneath ultraviolet rays and greenish-yellow in the dark, as explored by CIE Lab and luminescence spectral analyses. The morphology of the lanthanide-doped aluminate nanoparticles (43-98 nm) was examined by transmission electron microscopy (TEM). The morphologies and chemical composition of the luminescent glass@epoxy substrates were determined by different analytical techniques. The mechanical properties of the developed photoluminescent glass@epoxy substrates were inspected to show improved scratch resistance as compared to the AEA-free substrate. The photoluminescence spectra were measured to indicate the detection of two emission bands at 494 and 525 nm when excited at 365 nm. The photoluminescent glass@epoxy hybrids with lower AEA contents have showed fast reversibility of photochromism. On the other hand, the glass@epoxy substrates with higher phosphor contents underwent persistent luminescence. Results showed that the luminescent colorless glass@epoxy hybrids have enhanced superhydrophobicity and ultraviolet blocking.

Preparation of photoluminescent nanocomposite ink for detection and mapping of fingermarks.

Simple and efficient detection and mapping method based on a strong turn-on fluorescent pigment was developed for fingerprint analysis. We present a phosphor powder characterized by strong emission which is useful to achieve better fingerprint detection on multicolored or photoluminescent surfaces, such as currency notes characterized by optically changeable inks and highly fluorescent positions, because it offers better contrast and reduce the difficulty of background interference. Novel photochromic ink was prepared to establish a fingerprinted colorless film onto cellulose documents with green emission for anticounterfeiting applications as illustrated by photoluminescence spectra. Inorganic/organic nanoscale composite ink was prepared from rare-earth doped aluminate phosphor nanoparticles (PNPs; 27-49 nm) dispersed in a polyacrylic acid binding agent. PNPs were dispersed efficiently in polyacrylic acid to generate a colorless mark. The produced photochromic inks were spray-coated onto off-white paper sheets enclosing invisible fingermarks, and then exposed to thermofixation. Photochromic film was detected on paper surface presenting a transparent appearance under visible daylight and switchable to green under UV light. The CIE Lab parameters and photoluminescence spectra were studied under visible light and ultraviolet irradiation. The fingerprinted sheets showed fluorescence band at 517 nm upon excitation at 366 nm, showing a bathochromic shift and reversible photochromism without fatigue. The morphologies of pigment phosphor particles and fingerprinted sheets were inspected. The rheological properties of ink and mechanical behavior of the fingerprinted paper samples were explored. HIGHLIGHTS: Novel smart ink with alkaline-earth aluminate and polyacrylic acid was developed. Dual-mode fluorescent photochromism was presented for latent fingerprint analysis. Off-white fingerprinted films under daylight showed color change to green under UV. Fluorescence band monitored at 517 nm upon excitation at 366 nm. Fluorescent fingermark on paper sheets demonstrated good photostability.

Photosensitive Behavior Studies of the Ba3CaSi2O8:Eu3+ and aCeSiO4:Eu3+Luminescence Material Synthesis

Phosphors made from inorganic oxides and activated with rare earth metals are usedin numerous practical contexts. These include cathode ray tubes, high-efficiency luminouslights, x-ray radiography screens, field emission display panels, and many more.Inorganic phosphor compounds come in a wide variety of forms and have a wide variety ofpracticalapplications. Because of their many advantageous characteristics, including highquantumefficiency, long persistence of the phosphorescence, good stability, and the fact thataluminate-based phosphor is an excellent host material for the lamp industry, aluminatephosphors havea promising future in practical applications. Divalent europium ion dopedsynthetic hexagonal alkaline earth aluminate is an effective luminescence material. Plasmadisplays, field emission displays, fluorescence lamps, etc. all make use of phosphors based onaluminates.Nanophosphors based on the silicates Ba3CaSi2O8 and NaCeSiO4 havebeen produced at 900 ℃using the sol-gel process and doped with Eu3+. Fouriertransform infrared analysis (FTIR), X-ray powder diffraction (XRD), and photoluminescence(PL) techniques were used to examine the bonding, crystalline structure, andphotoluminescence properties of the produced nanophosphors. Europium doped bariumcalcium silicate (Ba3CaSi2O8:Eu3+) and sodium cerium silicate (NaCeSiO4:Eu3+) phosphorsemitted a red glow when exposed to ultraviolet (UV) light. The excitation and emission spectrawere analysed to determine the luminescence parameters of the produced phosphor. Based onXRD analyses, we know that the produced minerals Ba3CaSi2O8:Eu3+ and NaCeSiO4:Eu3+have orthorhombic and cubic structures, respectively, and have sizes of 46.36 nm and 28.57nm. The crystallinity of the finished products was uncovered by XRD analysis. Vacuumfluorescent displays, cathode ray tubes (CRT), safety indicators, luminous paints, fabrics, etc.all benefit from the optoelectronic characterisation of produced phosphors.

Preparation of photoluminescent and photochromic smart glass window using sol-gel technique and lanthanides-activated aluminate phosphor

Long-persistent photoluminescent and photochromic glass material capable of changing color under UV irradiation has been produced. With the simple immobilization of alkaline earth aluminate nanoparticles, a photoluminescent translucent glass has been created by the sol-gel method. The glass substrates were shown to change color to green under UV light, as demonstrated by CIE Lab screening. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to study both morphology and composition of the phosphor nanoparticles. On the other hand, the morphologies and chemical contents of the photoluminescent glass samples were examined using scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and X-ray fluorescence (XRF). The mechanical behavior of the prepared luminescent glasses was studied to show better resistance to scratching in comparison to the phosphor-free glass. Aside from that, the spectrum characteristics of photoluminescence excitation and emission were examined in depth. The luminescent glass substrates had two emission intensities of 427 and 522 nm monitored upon excitation at 371 nm. Samples of luminescent glass with lower phosphor levels had rapid reversibility of photochromism, whereas those with greater phosphor contents underwent long-lasting luminosity, similar to that of a flashlight that might substitute for electrical power. Results demonstrated that the photoluminescence colorless glass substrates have improved hydrophobicity and UV shielding.

Production of photoluminescent transparent poly(methyl methacrylate) for smart windows.

Photochromic and long-lasting photoluminescent transparent, rigid, ultraviolet (UV) protective and superhydrophobic poly(methyl methacrylate) (PMMA) plastic able to switch colour beneath UV irradiation was developed. Photoluminescent transparent PMMA plastic was prepared by the simple polymerization process of methyl methacrylate immobilized with alkaline earth aluminate (AEA) nanoparticles. These colourless PMMA plastic substrates showed a colour switch to greenish underneath UV light as proved using CIELAB screening. The morphology of AEA was evaluated using transmission electron microscopy. Conversely, transparent PMMA samples were evaluated using energy-dispersive X-ray spectra, scanning electron microscope, X-ray fluorescence spectroscopy and for hardness properties. Additionally, the photoluminescence properties were explored by studying excitation and emission spectra. The produced luminescence colourless PMMA plastic substrates displayed excitation band at 370 nm, and three emission peaks at 433, 494 and 513 nm. Photoluminescent PMMA with lower contents of AEA showed fast and reversible photochromism under UV light, while PMMA samples with higher contents of AEA showed long-lasting luminescence such as a flashlight with the ability to replace electric power. The findings showed that the produced photoluminescence colourless PMMA plastic substrates exhibited enhanced UV shielding and superhydrophobicity.

Highly transparent, writable and photoluminescent foldable polymer film: When fluorescent dyes or pigments join cellulose-based microgel

We prepared a self-dispersed cellulose-based microgel via chemically bonding hydrophilic gelatin peptide chain onto cellulose glucose chain. Following, a variety of highly transparent, foldable, and writable photoluminescent polymer films was obtained through loading organic dyes and inorganic pigments onto cellulose-based microgel matrix, respectively. Benefiting from the coupling sites and network effect of microgel as well as the abundant hydroxyl, amino, and imino groups in its structure, the microgel containing organic dyes and inorganic pigments exhibit good dispersion and stability, and the resultant photoluminescent films emit bright yellow, orange, yellow-green, and blue-green fluorescence under UV light, respectively, especially the cellulose-based microgel stabilized inorganic alkaline earth aluminate hybrids exhibit continuous luminescence for a long time in the dark. Compared with the existing regenerated cellulose or CNCs-based fluorescent films, the cellulose-based microgel fluorescent films present higher transmittance and good biodegradability. This study can bring new ideas for the development of flexible luminescent devices.

Recent Developments in Lanthanide-Doped Alkaline Earth Aluminate Phosphors with Enhanced and Long-Persistent Luminescence.

Lanthanide-activated alkaline earth aluminate phosphors are excellent luminescent materials that are designed to overcome the limitations of conventional sulfide-based phosphors. The increasing research attention on these phosphors over the past decade has led to a drastic improvement in their phosphorescence efficiencies and resulted in a wide variety of phosphorescence colors, which can facilitate applications in various areas. This review article discusses the development of lanthanide-activated alkaline earth aluminate phosphors with a focus on the various synthesis methods, persistent luminescence mechanisms, activator and coactivator effects, and the effects of compositions. Particular attention has been devoted to alkaline earth aluminate phosphors that are extensively used, such as strontium-, calcium-, and barium-based aluminates. The role of lanthanide ions as activators and coactivators in phosphorescence emissions was also emphasized. Finally, we address recent techniques involving nanomaterial engineering that have also produced lanthanide-activated alkaline earth aluminate phosphors with long-persistent luminescence.

Evolution of Monoclinic CaAl2O4 Nanocrystallites via Chemical Route and Its Optical Investigations

Nanocrystalline calcium aluminate (CaAl2O4) powder is an adequate phosphor material. Calcium aluminate is a versatile member belongs to a category of alkaline earth aluminates phosphor. It has multifaceted applications in different areas such as photocatalysis, sensing, optoelectronic devices, displays, and imaging etc. In the present study, calcium aluminate has been prepared by well-known citrate sol-gel technique. X-ray diffraction (XRD) method has been used to analysis the amorphous and crystalline behavior of the prepared samples. The sample annealed at 800° indicates the monoclinic phase with enhanced intensity of the prominent diffraction peaks. By using Debye-Scherrer formula the grain size of crystalline powder is calculated ~10 nm. FTIR spectra confirmed the molecular orientation and bond structure in the prepared nanomaterial. Surface morphology and elemental composition present in prepared samples has been examined by Scanning electron microscope and energy dispersive spectroscopy. Uv-vis spectroscopy result showed red shift in the nanopowder with thermal treatment. In material science, due to their long-lasting photo-luminescence properties in visible region these aluminates are very attractive for evolution of new generation inorganic phosphor materials.

VUV investigation of blue emitting MAl12O19: Eu (M = Ca, Sr, Ba) phosphors synthesized by combustion method

. Synthesis of europium doped alkaline earth aluminates MAl12O19 [M=Ca, Sr, Ba] by low temperatures (500ºC) solution combustion method. It corresponds to maintain the ratio of metal nitrate and urea solution mixtures. The characterization of Eu doped MAl12O19 [M=Ca, Sr, Ba] materials were done by X-ray diffraction, scanning electron microscope analysis and the optical properties were studied under 147 nm and 172 nm from synchrotron radiation excitation. The Eu-doped MAl12O19 phosphor shows broad and strong absorption in VUV region and exhibits intensive emission in blue region. The CaAl12O19: Eu2+ shows strong blue emission band at 414 nm while in SrAl12O19:Eu2+ two emission peaks are observed at about 395 nm and another around 418 nm. Both CaAl12O19: Eu2+ and SrAl12O19:Eu2+ display two very weak red emission bands at 592, 613 and 591, 613 nm respectively due to co-existence of Eu3+. BaAl12O19: Eu2+ phosphor shows emission around 440 nm in the blue region of the spectrum.

Enhanced upconversion from Er3+/Yb3+ co-doped alkaline earth aluminates phosphor in presence Zn2+: A comparative study

Abstract In the present work, the upconversion emission spectra of Er3+/Yb3+co-doped CaAl2O4 (CAO), SrAl2O4 (SAO) and BaAl2O4 (BAO) phosphor samples have been studied in absence and presence of Zn2+. The samples were synthesized using high temperature solid state reaction technique at 1623 K. The X-ray diffraction (XRD) measurements have been carried out to verify the pure phase formation in all the three cases. Whereas the CAO and SAO samples show the monoclinic phase, the BAO sample shows hexagonal phase. The surface morphology of the three phosphor samples has been studied by scanning electron microscopy (SEM) technique. The Fourier-transform infrared (FTIR) and Raman measurements show the vibrational bands due to different groups present in the samples. The upconversion emission spectra of all the three samples show green and red emissions bands due to Er3+ ion on excitation with 980 nm laser. However, it is interesting to note that CAO phosphor emits very intense green and weak red emissions, the SAO and BAO phosphors give intense red and weak green emissions. However, the upconversion emission intensity (green as well as red both) in all the three samples is enhanced several times in presence of Zn2+ ions. The mechanism involved in UC emissions has been explained by partial energy level diagram.

Tailoring the emission of Eu based hybrid materials for light-emitting diodes application

The rare-earth elements (REEs) derived phosphors play an essential role in light-emitting diodes. Many approaches have been proposed for tailoring the emission color of lamp phosphors by tuning the contents and valances of REEs (such as Ce3+, Tb3+, Eu3+). As we know, the separation and purifying of REEs from waste phosphors usually requires high cost and complicated operations. Here we report the phosphor only based on Eu doped in different matrices with manipulated color for the first time, which will minimize the environmental challenges present in the transition to a green economy. The hybrid material is manufactured by mixing (SAOE) SrAl2O4:Eu2+ and (TTAE) Eu(TTA)3phen (TTA = 2-thenoyltrifluoroacetone, phen = 1,10-phenanthroline) in different mass ratios. The optical properties of the resulting phosphor materials are determined by photoluminescence (PL). Eu doped in alkaline earth aluminates (SrAl2O4) has strong green (510 nm) emission, meanwhile the Eu exhibits enhanced red (612 nm) luminescence upon bonding with TTA (thenoyltrifluoroacetone) and phen ligands. By adjusting the mass ratios of SAOE and TTAE, the emission colors of the hybrid materials can be tuned from red to green. The chromaticity coordinates are calculated, which fell well in the red, orange, yellow and green regions of 1931 CIE chromaticity diagram. According to the spectroscopic studies, the absorption almost have no overlap on the emissions of SAOE and TTAE powders, leading to efficient PL emitting with high photoluminescence quantum yields of 24–68%. Through deposition of the hybrid materials with polydimethylsiloxane (PDMS) onto the 365 nm UV-LED chip, tunable color light-emitting diodes are fabricated, they show excellent luminescence properties, indicating their potential application in optical device and offering a novel approach for designing multi-color phosphor materials.

D\u2013f luminescence of Ce3+ and Eu2+ ions in BaAl2O4, SrAl2O4 and CaAl2O4 phosphors

Ce3+ and Eu2+ doped alkaline earth aluminates MAl2O4 (M = Ca, Sr, Ba) were prepared by single-step combustion synthesis at low temperature (600 °C). X-ray diffraction (XRD) analysis confirmed the formation of BaAl2O4, CaAl2O4, and SrAl2O4. Photoluminescence spectra and optimal luminescent properties of Ce3+ and Eu2+ doped MAl2O4 phosphors were studied. Relation between Eu2+ and Ce3+ f–d transitions was explained. Spectroscopic properties known for Ce3+ were used to predict those of Eu2+ by using Dorenbos’ method. The values thus calculated were in excellent agreement with the experimental results. The preferential substitution of Ce3+ and Eu2+ at different Ba2+, Sr2+, Ca2+ crystallographic sites was discussed. The dependence of emission wavelengths of Ce3+ and Eu2+ on local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Experimental results matched excellently with the predictions of Dorenbos’ and Van Uitert’s models.

The optical properties of Sr3SiAl10O20 and Sr3SiAl10O20:Mn4+

Mn4+-activated luminescent materials have attracted significant attention recently. In particular, alkaline earth aluminates, such as Sr4Al14O25:Mn4+ and CaAl12O19:Mn4+, emit light in the red region, which can be exploited in phosphor-converted LEDs. We applied a sol-gel precursor followed by a ceramic method to synthesize highly crystalline Mn4+-doped Sr3SiAl10O20. The compound Sr3SiAl10O20:Mn4+ exhibits deep red photoluminescence that peaks at 663 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d.3 configuration) within the [MnO6]8− octahedra on the aluminum site in the Sr3SiAl10O20 (Space group C12/m1) host structure. The photoluminescence properties, such as the temperature dependence of the luminescence intensity and luminescence lifetime, are presented. Furthermore, the luminescence intensity as function of the activator concentration was investigated. Additionally, the band structure of the undoped host material was treated with Density Functional Theory (DFT). The theoretical results were evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, the crystal field and Racah parameters were extracted to compare with those reported in the literature.

Tb3+-doped alkaline-earth aluminates: Synthesis, characterization and optical properties

Un-doped and Tb3+-doped calcium and strontium aluminates (CaAl2O4, CaAl2O4:Tb3+, SrAl2O4, SrAl2O4:Tb3+) were synthesized by a new soft chemical method—the precursor route via the thermal decomposition of tartarate compounds. The complex precursors have been characterized by elemental chemical analysis, infrared spectroscopy (IR), luminescence spectroscopy and thermal analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM), IR and Raman spectroscopy (RS) were used for the structural and morphological characterization of un-doped and doped alkaline-earth aluminate powders. Photoluminescence (PL) and Thermoluminescence (TL) properties of the aluminates were also investigated. The XRD patterns confirmed the formation of low-temperature structures: hexagonal structure for CaAl2O4 and monoclinic structure for SrAl2O4, with average crystallite size of 64nm and 46nm for CaAl2O4 and SrAl2O4, respectively. Microstructural analysis by SEM showed the homogeneous microstructure and fine particle size of the powder obtained by precursor method.

Hydrothermal Synthesis and Luminescent Properties of Eu3+ Doped Sr3Al2O6 Phosphor for White LED.

Eu3+ ions doped Sr3Al2O6 phosphors were successfully synthesized via a hydrothermal method. The precursor was prepared by low temperature hydrothermal method using ammonia as both alkaline source and precipitator. Then the final product was obtained by high temperature sintering. In addition, the structures, morphologies, and luminescent properties of as-prepared products were thoroughly characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Fluorescence spectroscopy (PL). XRD shown a single phase Sr3Al2O6 prepared by a facile hydrothermal method at 250 °C for 10 h. In the PL spectra of as-prepared samples, the optimal value of Eu3+ concentration is 2 mol%. From the fluorescent spectra, the emission peaks of Sr3Al2O6: Eul+ phosphors are centered at around 591 nm, and the excitation peaks are centered at around 233 nm, 323 nm, 394 nm, and 468 nm, respectively, which were assigned to the characteristic transition of Eu3+ ions. The influence of ammonia, and the synthesis temperature on the luminescent properties of Sr3Al206: Eu3+ phosphors were studied in detail. The alkaline earth aluminates luminescent materials activated by rare earth ions have good prospects in the field of new-generation light sources.

Effect of Composition and Impurities on the Phosphorescence of Green-Emitting Alkaline Earth Aluminate Phosphor.

Recent improvements to SrAl2O4:Eu2+, Dy3+ phosphors have enabled the use of luminescent hosts with a stable crystal structure and high physical and chemical stability, thus overcoming the bottleneck in the applicability of ZnS:Cu phosphors. However, enhancement of afterglow lifetime and brightness in SrAl2O4:Eu2+, Dy3+ phosphors remains a challenging task. Here, we have improved the afterglow characteristics in terms of persistence time and brightness by a systematic investigation of the composition of Eu-doped alkaline earth aluminate SrAl2O4:Eu2+, Dy3+ crystals. We found that a Dy3+/Eu2+ ratio of ~2.4 and ~0.935 mol Eu2+ (per mol of SrAl2O4) gave the brightest and longest emissions (11% and 9% increase for each). Doping with Si4+ also resulted in a slight increase in brightness up to ~15%. Doping with alkali metal or alkaline earth metal significantly enhanced the phosphorescence intensity. In particular, doping with 0.005 mol Li+ (per mol of SrAl2O4) alone boosted the phosphorescence intensity to 239% of the initial value, as compared to that observed for the non-doped crystal, while doping with 0.01 mol Mg2+ and 0.005 mol Li+ (per 1 mol SrAl2O4) boosted the phosphorescence intensity up to 313% of the initial value. The results of this investigation are expected to act as a guideline for the synthesis of bright and long persistent phosphors, and facilitate the development of persistent phosphors with afterglow characteristics superior to those of conventional phosphors.

Photocatalytic Characteristics For The Nanocrystalline TiO2 Supported On Sr4Al14O25: Eu2+, Dy3+ Phosphor Beads

The photocatalytic behaviors of TiO2-supported on the long lasting phosphor beads were examined. Nanocrystalline TiO2 was coated on ellipsoidal-spherical beads of an alkaline earth aluminate phosphor, Sr4Al14O25:Eu 2+ , Dy 3+ , by low pressure chemical vapor deposition (LPCVD). The photocatalytic reaction was examined by measuring the decomposition of benzene and toluene gases by gas chromatography under ultraviolet, visible light (λ> 410 nm) irradiation, as well as in the dark. The LPCVD TiO2coated Sr4Al14O25:Eu 2+ , Dy 3+ showed an active photocatalytic reaction under visible irradiation. The mechanisms of the photocatalytic reactivity for the TiO2-coated Sr4Al14O25:Eu 2+ , Dy 3+ phosphor beads were discussed in terms of the crystal structure at the interface, energy band structure and phosphorescence. The coupling of TiO2 with the Sr4Al14O25:Eu 2+ , Dy 3+