Long Afterglow SrAl2O4:Eu2+,Dy3+ Phosphors as Luminescent Down‐Shifting Layer for Crystalline Silicon Solar Cells

SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors can convert near ultraviolet light with lower sensitivity to the solar cell to yellow‐green light at which the solar cell has higher sensitivity and exhibit the excellent luminescent property of long persistence. Therefore, in this study, the authors firstly synthesized the fine SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors and then produced SrAl₂O₄:Eu²⁺,Dy³⁺/SiO₂ composite films as spectral shifters to understand the effects of SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor on photoelectric conversion efficiencies of a crystalline silicon photovoltaic module. Under one sun illumination, the composite film containing an appropriate amount of SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor enhances the photoelectric conversion efficiency of the cell through spectral down‐shifting as compared to the bare glass substrate, and the maximum achieves 11.12%. In contrast, the commercial SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor composite film is not effective for improving the photoelectric conversion efficiency because of the relatively lower visible light transmittance of film caused by the large aggregates. After one sun illumination for 1 min, the light source was turned off, and the cell containing the synthesized SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor still shows an efficiency of 1.16% in the dark due to the irradiation by the long persistent light from SrAl₂O₄:Eu²⁺,Dy³⁺, which provides a possibility to fulfill the operation of solar cells even in the dark.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>,<Emphasis Type="Italic">RE</Emphasis><Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and Dy³⁺ codoped strontium aluminates SrAl₂O₄: Eu²⁺,Dy³⁺ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu²⁺ ion doped in SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy³⁺ ion introduced into SrAl₂O₄: Eu²⁺ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy³⁺ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE ³⁺ ions have a different effect on persistent luminescence. Only the RE ³⁺ ions (for example, Dy³⁺ and Nd³⁺), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl₂O₄: Eu²⁺. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated. The text was submitted by the authors in English.     

Sunlight‐activated long persistent luminescent polyurethane incorporated with amino‐functionalized SrAl2O4:Eu2+,Dy3+ phosphor

An amino‐terminated long persistent luminescent phosphor (Amino‐SrAl₂O₄:Eu²⁺,Dy³⁺) was prepared based on inorganic SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor, chemically modified with 3‐aminopropyltriethoxysilane (KH550). Fourier transform infrared and X‐ray photoelectron spectral, thermogravimetric and scanning electron microscopic measurements confirmed the successful synthesis of Amino‐SrAl₂O₄:Eu²⁺,Dy³⁺. Then this amino‐functionalized phosphor was introduced into polyurethane (PU) through urea linkages, and the effects of the chemical combination of Amino‐SrAl₂O₄:Eu²⁺,Dy³⁺ and PU on the morphology, structure, storage stability, and mechanical, thermal and luminescent properties of the resultant long persistent luminescent polyurethane (LPLPU) were investigated. Compared with SrAl₂O₄:Eu²⁺,Dy³⁺/PU composites prepared by physical blending, the LPLPU shows better mechanical properties and storage stability due to the good compatibility of Amino‐SrAl₂O₄:Eu²⁺,Dy³⁺ with PU. More residues and higher initial decomposition temperature are observed because the interaction of the amino‐phosphor and PU delays the degradation. Study of the luminescent effect reveals that the LPLPU shows more than 10 h afterglow after cessation of the excitation light, and the brightness of green light in darkness is basically the same as that of LPLPU and SrAl₂O₄:Eu²⁺,Dy³⁺/PU. © 2016 Society of Chemical Industry     

Effects of adding B<Subscript>2</Subscript>O<Subscript>3</Subscript> as a flux on phosphorescent properties in synthesis of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: (Eu<Superscript>2+</Superscript>, DY<Superscript>3+</Superscript> phosphor

SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was prepared by solid state reaction. B₂O₅ as a flux was added in SrAl₂O₄:(Eu ²⁺, Dy³⁺) in order to accelerate a solid state reaction. In this paper, the effects of B₂O₃ on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B₂O₃ contents. The maximum afterglow intensity of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was obtained at the B₂O₃ content of 5%. Adding the B₂O₃ caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and Β angle of the SrAl₂O₄ crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation of Eu²⁺ ions. The afterglow characteristic of the SrAl₂O₄: (Eu²⁺, Dy³⁺) phosphor was thus enhanced.     

Effect of Al/Sr ratio on the luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

Recent studies have brought out many phosphors like Eu²⁺, Dy³⁺-doped alkaline earth aluminates. The trivalent Dy³⁺ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission.In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu²⁺ and Dy³⁺ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis.A variety of strontium aluminates, such as SrAl₂O₄, Sr₄Al₂O₇, Sr₃Al₂O₆, Sr₃Al₂(Eu, Dy, Y)O_7.5, Al₅(Eu, Dy, Y)O₁₂, Sr₄Al₁₄O₂₅, SrAl₁₂O₁₉ and (Eu, Dy, Y)AlO₃ have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl₄O₇ phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl₂O₄ phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition.     

Atomic layer deposition (ALD) of nanoscale coatings on SrAl2O4-based phosphor powders to prevent aqueous degradation

The aqueous degradation of Eu²⁺-activated and Dy³⁺-codoped strontium aluminate (SrAl₂O₄:Eu²⁺, Dy³⁺, SA2-Green) long afterglow phosphors synthesized from solid-state reaction and coated with nanoscale metal oxide protective layers (≤12 nm) via atomic layer deposition (ALD) is investigated. Uncoated phosphor powders degrade rapidly upon water immersion and lose their green phosphorescence within 48 hours of water exposure. Postmortem investigations reveal hydration and decomposition of the SrAl₂O₄ phase. ALD of ~10 nm Al₂O₃ or ~12 nm TiO₂ is found to significantly improve the powder's resistance to aqueous degradation. All ALD-coated powders show minimal structural and chemical degradation and retain phosphoresence after 48 hours of water immersion. This enhanced durability offers a new pathway for applying long afterglow phosphors to outdoor applications like roadway markings or safety signage and for their incorporation into more eco-friendly waterborne coatings.     

Characterization of strontium aluminate phosphors prepared from milled SrCO3

SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors were prepared by solid-state reaction from milled SrCO₃. The effect of milling treatment of SrCO₃ on the formation and physical properties of SrAl₂O₄ phosphors was investigated by DTA, XRD, BET, SEM and PL. The results indicate that small crystallite size and large specific surface area of the milled SrCO₃ were able to increase the contact points between the reactants and to reduce the average transport distance for materials diffusion. Therefore, the solid-state reaction can be accelerated and the formation of SrAl₂O₄ was facilitated. On the other hand, the number of nucleation sites was also suggested to be increased that leads to a decrease in SrAl₂O₄ crystallite size and an increase in specific surface area. The increased specific surface area was proposed to increase the emission intensity and afterglow decay.     

Influence of Bi2O3 flux in the structural and photoluminescence properties of SrAl2O4:Eu2+ phosphors

SrAl₂O₄:Eu²⁺ phosphors with various content of Bi₂O₃ flux were synthesized and analyzed. It was observed that the crystallinity and the particle size of the phosphors were increased with the addition of Bi₂O₃ flux. These phenomena are considered to be caused via the melting of the Bi₂O₃ flux particles during the synthesis of the phosphors. The melted Bi₂O₃ flux increased the mobility and homogeneity of solid reactants, thereby enhancing the photoluminescence intensity of the phosphors. SrAl₂O₄:Eu²⁺ phosphors with Bi₂O₃ as the flux exhibited a broad green emission with a peak at 520 nm. The highest photoluminescence emission intensity was observed when 5 mol% Bi₂O₃ flux was added into the phosphors. The emission is due to 4f⁶5d→4f⁷ (⁸S_7/2) transitions of the Eu²⁺ ions. Moreover, Bi₂O₃ flux extended the application of the ultraviolet excited phosphors toward the blue-light excited phosphors. Nevertheless, the influence of Bi₂O₃ on the afterglow and the emission color of SrAl₂O₄:Eu²⁺ phosphors were not significant. This research indicated that Bi₂O₃ flux is effective flux for synthesizing SrAl₂O₄:Eu²⁺ phosphors.     

Tunable full-color emission phosphors: Enhanced security application via a patterned 3-dimensions code

Developing tunable full-color emission photoluminescent materials is always desired in color-on-demand applications and still confronts challenges. Theoretically, full color including white emission can be achieved by the combination of three primary colors (red, green, and blue) based on the additive color theory. Herein, a strategy for the preparation of tunable full-color luminescence is realized by mixing the inorganic rare-earth-doped SrAl₂O₄: Eu²⁺, Dy³⁺ (green emission), Y₂O₂S: Eu³⁺, Mg²⁺, Ti⁴⁺, Ti⁴⁺_0.05 (red emission), and Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ (blue emission) phosphors with different ratios. By adjusting individual phosphors at certain specific ratios, white light (0.332, 0.332) and full-spectra emission are achieved under a single low excitation energy (λ_ex = 365 nm) using a portable ultraviolet (UV) lamp. Based on the facile preparation and effective tunable full-color emission features of the phosphors, a novel encryption way of the luminescent unit as information storage 3 dimensions (3D) codes is developed. The multiplexed encrypting information capacity of the codes is enhanced in a 3D maneuver strategy by simply adjusting the number of light-emitting units with infinite emission colors. The proposed strategy makes the tunable full-color emission phosphors useful in promising applications including full-color display, high-level information encryption and anti-fake.     

Preparation of strontium aluminate: Eu2+ and Dy3+ persistent luminescent materials based on recycling alum sludge

Eu²⁺ and Dy³⁺ doped strontium aluminate persistent luminescent materials are prepared by solid state reaction using alumina obtained from the alum sludge [1]. Three group compositions; Sr (NO₃)₂ with alumina (calcined at 1100 °C, ESA1), SrO with alumina (calcined at 1400 °C, ESA2) and Sr(NO₃)₂ with alumina (calcined at 1400 °C, ESA3) doped with Eu³⁺: Dy³⁺ ions in different molar ratios (1 Eu³⁺: 2Dy³⁺, 1.5 Eu³⁺: 1.5Dy³⁺, 2Eu³⁺:1Dy³⁺ and 2.5Eu³⁺: 0.5 Dy³⁺) were prepared. The samples were fired under different under active carbon at 1250 °C. Surface morphology, crystalline structure, Photoluminescence measurements and the decay characteristic were characterized by SEM, XRD, and the photoluminescence spectrometers, respectively. The effect of the firing temperature at 1250 °C was also determined by apparent porosity and bulk density measurements. The results indicated that the main composition of the samples fired under active carbon powder was strontium aluminate with a very small amount of secondary phases. The results showed that the samples fired under active carbon had good phosphorescence properties and good decay time. A broad band UV-excited luminescence of the SrAl₂O₄:Eu²⁺, Dy³⁺ phosphorescent pigments was observed at λ_max = 517 nm due to transitions from 4f⁶, 5d¹ to 4f⁷ configuration of the emission center (Eu²⁺ ions). Photoluminescence spectra for ESA1 group show higher intensity than that of ESA2 and ESA3 groups. The difference in the behavior of the photoluminescence spectra for the three groups can be attributed to (i) different synthesis methods and (ii) the presence of different mixed phases (major SrAl₂O₄ and secondary phases).     

Tunable white light and energy transfer of Dy3+ and Eu3+ doped Y2Mo4O15 phosphors

A series of Dy³⁺ or/and Eu³⁺ doped Y₂Mo₄O₁₅ phosphors were successfully synthesized at a low temperature of 600 °C via solid state reaction. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL) excitation, emission spectra and PL decay curves. XRD results demonstrate that Y₂Mo₄O₁₅: Dy³⁺, Eu³⁺ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy³⁺ and Eu³⁺ ions activated Y₂Mo₄O₁₅ phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y₂Mo₄O₁₅: 0.08Dy³⁺, yEu³⁺ phosphors can be adjusted by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions and a white light is achieved when the doping concentration of Eu³⁺ is 5%. In addition, the energy transfer from Dy³⁺ to Eu³⁺ is also confirmed based on the luminescence spectra and decay curves.     

Highly efficient photostimulated luminescence of Pb2+ doped SrAl2O4:Eu2+, Dy3+ borate glass for long-term stable optical information storage

Despite the transformative role in society, information storage materials remain vulnerable to the corrosion by water, oxygen and heat, while topological engineering of glass provides an attractive solution to this tricky problem. Here, a considerable discovery is reported that the doping of Pb²⁺ ions could greatly affect the luminescence behavior of SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass, resulting in a controllable property between long persistent luminescence and photostimulated luminescence. Specifically, high concentration Pb doped samples featuring the deeper continuously distributed trap levels with 0.97–1.47 eV performed highly efficient photostimulated luminescence. In other words, the ultraviolet-visible photons could be “written” in the deeper traps and then “read out” under the stimulation of a 980 nm near-infrared laser. From the combined structural and luminescence characterizations, it was speculated that the deeper trap originated from the increase of oxygen vacancies at defect levels. The practical anti-counterfeiting application was successfully realized based on this material with superior photostimulated luminescence phenomenon, which rendered the SrAl₂O₄:Eu²⁺, Dy³⁺ borate glass shine in a new field such as anti-counterfeiting, yet as a promising candidate for information storage application.     

Enhanced Light Storage of SrAl2O4 Glass‐Ceramics Controlled by Selective Europium Reduction

A luminescent Eu, Dy: SrAl₂O₄ glass‐ceramics with high transparency in the visible region was successfully synthesized using the frozen sorbet technique with the control of O₂ partial pressure () for the oxidation of Eu²⁺ ions. The glass‐ceramics include Eu²⁺, Eu³⁺, and Dy³⁺ ions, and thus exhibits three characteristic types of emission bands, 4f–5d at around 520 nm (Eu²⁺ ions), 4f–4f at 610 nm (Eu³⁺ ions), and 480 nm (Dy³⁺ ions). The Eu, Dy: SrAl₂O₄ glass‐ceramics provide remarkable long‐persistent luminescence under dark condition. The glass‐ceramics also exhibits color‐changing luminescence in the visible region based on their remarkable light storage properties. The luminescent Eu, Dy: SrAl₂O₄ glass‐ceramics using the frozen sorbet technique with control of are promising materials for application in novel photonic and light storage materials.     

Alumina encapsulated SrAl2O4:Eu, Dy phosphors

Alumina encapsulation on SrAl₂O₄: Eu²⁺, Dy³⁺ phosphors by a new type of chemical precipitation process was reported for the first time to the best of our knowledge. X-ray fluorescent measurements revealed that using glycol instead of the distilled water as the disperse medium is helpful to alumina encapsulation. Scanning electron micrographs and BET measurements showed that a dense and homogeneous off-white alumina layer was formed on the phosphor surface after encapsulation. Water resistance and heat resistance measurements showed that when the encapsulation amount reached to 5 wt.% (fed value), the encapsulated phosphors began to show good water resistance and heat resistance with little loss of persistent phosphorescence.     

Red-shift and improved afterglow of Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors via a cation substitution strategy

Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f⁶5 d¹→4f⁷ of Eu²⁺. Upon the same excitation, the B³⁺-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphors display red-shift from 609 nm to 625 nm with increasing B³⁺ concentrations. The XRD patterns show that Al³⁺ can be replaced by B³⁺ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺is rather weak, while the sample co-doped with B³⁺shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B³⁺ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B³⁺ ions caused redshift and enhanced afterglow for the Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphor.     

Photoluminescence characteristics and mechanism of SrAl2O4 co-doped with Eu3+ and Cu2+

SrAl₂O₄ co-doped with Cu²⁺ and Eu³⁺ was prepared at high temperature in a weakly oxidizing atmosphere by solid states reaction. X-ray diffraction (XRD) pattern of the sample shows that the doped sample exhibits SrAl₂O₄ crystalline phase. No characteristic peaks of dopant have been observed in XRD pattern of doped sample. The excitation and emission spectra of CuEu:SrAl₂O₄, Eu:SrAl₂O₄, Cu:SrAl₂O₄ samples consist of many sharp peaks. The excitation and emission spectra of the SrAl₂O₄ sample co-doped with Cu²⁺ and Eu³⁺ are significantly different from those of Eu:SrAl₂O₄ and Cu:SrAl₂O₄ samples. The novel photoluminescence (PL) characteristic of the co-doped sample is attributed to the composite luminescence of Cu²⁺ and Eu³⁺ ions in SrAl₂O₄ matrix.     

Eu2+, Dy3+: Sr2B5O9Cl,a new blue-emitting phosphor with long persistence

A new Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphor with long persistence was synthesized in a reducing atmosphere by a solid-state reaction process. The pure-phase phosphor was obtained by calcination at 900 °C. The introduction of Eu²⁺ into the lattice of the matrix resulted in a broad blue emission centered at 423 nm, which was due to the characteristic 4f6⁵d¹ to 4f⁷ energy transfer of Eu²⁺ ions. Both Eu-doped and Dy/Eu-codoped phosphors displayed afterglow behaviors due to the electron traps generated by the incorporation of tri-valanced rare earth cations into the original Sr lattice sites. The afterglow of Eu²⁺: Sr₂B₅O₉Cl and Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphors showed standard double exponential decay behaviors, and the Eu²⁺/Dy³⁺ co-doped sample demonstrated better afterglow properties than Eu²⁺-doped one. A longer lifetime for the electrons was confirmed after the afterglow decay curve simulation. Based on the analysis of thermally stimulated luminescence (TSL), the difference in afterglow was attributed to the different trap concentrations induced by the Dy³⁺ (Eu³⁺) doping in the Sr₂B₅O₉Cl matrix.     

Preparation and luminescence of SrAl2O4: Eu2+,Dy3+ phosphors coated with maleic anhydride

In this paper, maleic anhydride is directly coated on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ (SAO‐ED) phosphors by an interfacial coordination chemistry method. Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectra (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) methods are used to characterize the coating. The experimental result shows that a dense coating layer is consisting of maleic anhydride coordination with metal ions on the surface of the phosphors and the coating process does not destroy the crystal structure of the phosphors. It is also found that the introduction of maleic anhydride does not change the excitation and emission spectra of SAO‐ED phosphors, but decreases the luminous intensity, which is verified by the photoluminescence (PL) measurement. Afterglow delay curves show that the initial brightness of coated SAO‐ED phosphors decreases, but the afterglow decay rate of coated phosphors is slower than that of uncoated phosphors after they both are immersed into water for one month. This indicates that the coating layer protects the phosphors and the crystal structure of coated phosphors in water was not destroyed.     

Synthesis,energy transfer mechanism,and tunable emissions of novel Na3La(VO4)2:Re3+ (Re3+ = Dy3+, Eu3+, and Sm3+) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.     

Fabrication and characterizations of Eu2+-Dy3+ co-doped SrAl2O4 ceramics with persistent luminescence

(Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ persistent luminescence (PersL) ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) using H₃BO₃ as a sintering additive. The phase composition, microstructure, luminescence properties, trap state, and PersL performance of HIP post-treated (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics were discussed. For the (Sr_0.97Eu_0.01Dy_0.02)Al₂O₄ PersL ceramics after HIP post-treatment, the initial luminescence intensity of the ceramics reached over 6400 mcd/m² with simulated daylight irradiation of 1000 lx for 5 min, and the persistent emission decay time > 17 h. This is much better than the SrAl₂O₄:Eu²⁺,Dy³⁺ PersL powders and the other luminescent ceramics. In addition, this method is a solid-state reactive sintering method for synthesizing ceramics, which has the advantages of low cost and simple operation, and is suitable for large-scale, high-volume industrial production.