Characterization of luminescent SrAl2O4 films doped with terbium and europium ions deposited by ultrasonic spray pyrolysis technique

SrAl₂O₄, SrAl₂O₄:Tb³⁺ and SrAl₂O₄:Eu³⁺:Eu²⁺ films were synthesized by means of the ultrasonic spray pyrolysis technique. These samples, characterized by X-Ray Diffraction, showed the monoclinic phase of the strontium aluminate. Images of the surface morphology of these films were obtained by SEM and the chemical composition was measured by EDS and XPS. The photoluminescence and cathodoluminescence characteristics of the films were studied as a function of the terbium and europium concentrations. The optimal PL emission intensities were reached at 8?at% for terbium doped films and 6?at% for europium doped samples. The CL emission spectra for europium doped films showed the typical bands of Eu³⁺ ions and also a broadband centered at 525?nm which is attributed to Eu²⁺ ions. XPS measurements confirm the presence of Eu³⁺ and Eu²⁺ in europium doped SrAl₂O₄ films, without having been subjected to a reducing atmosphere. Chromatic diagrams exhibited green color for SrAl₂O₄:Tb³⁺ films, red and yellow colors for SrAl₂O₄:Eu³⁺:Eu²⁺ films. The PL decay curves were also obtained: the averaged decay time was 2.7?ms for SrAl₂O₄:Tb³⁺ films and 1.9?ms for SrAl₂O₄:Eu³⁺ films. Similar results were obtained by the stretched exponential model.     

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.     

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).     

Experimental evaluation of the luminescence performance of fired clay brick coated with SrAl2O4:Eu/Dy phosphor

This study evaluates the luminescence performance of fired clay bricks coated with SrAl₂O₄:Eu/Dy phosphor. To do so, SrAl₂O₄:Eu/Dy phosphor was first produced using the traditional solid-state reaction synthesis technique. The prepared phosphor was then used for coating fired clay bricks to analyze the luminescence performance via spectral analysis, decay characteristics, and microstructure of the bricks. The results reveal that excitation and emission spectra of the phosphor coated bricks range from 200 to 480 nm and 455 to 650 nm, respectively, suggesting that the phosphor coated bricks have the capacity of absorbing light with a wide range of wavelengths. The peak wavelength projected at 511 nm in the emission spectrum is achieved, which indicates 4f⁶5 d¹-4f⁷ transition of Europium (Eu²⁺). The repeated excitation and deexcitation of Eu²⁺ by using hole traps and trap levels offered by Dysprosium (Dy³⁺), exist between the ground and the excited state of Eu²⁺ leads to luminescent phenomenon. Moreover, the decay characteristics has revealed that phosphor coated bricks can emit light for a considerable amount of time (>8.5 min) upon the removal of the excitation source. The results reveal that phosphor coated bricks has the potential of increasing energy efficiency of residential and commercial buildings.     

Anomalous preparation,intense 5D0→7F4 emission and adjustable double center emission of Eu3+ and Eu2+ codoped Ca2Al2SiO7

A series of Eu³⁺/Eu²⁺ codoped Ca₂Al₂SiO₇ were synthesized by traditional solid-state synthesis in reducing atmosphere. In this work, XRD powder diffraction proved that the obtained sample was pure. Photoluminescence properties are characterized by excitation, emission spectra and decay curves. Double center emission is achieved by adjusting excitation wavelength and concentration. Under the 394 nm excitation, the emission spectra Ca₂Al₂SiO₇: Eu phosphors exhibit two bands situated at blue emission of 4f5d-4f transition from Eu²⁺ ion and red emission of 4f-4f transition coming from Eu³⁺ ion. The red and yellow light can be obtained when the concentration of doped europium ions is at 0.5% and 1%, respectively. When the excitation wavelength was 394, 280 and 584 nm, the emission color change from yellow to blue, respectively. The bond energy theory explains Eu²⁺ and Eu³⁺ ion occupy Ca1 site in the Ca₂Al₂SiO₇ lattices. In addition, the spectra show that the abnormal intensity peaks of europium ion at 701 nm can be found. Analysis of the related intensity ⁵D₀-⁷F₂(618 nm) transition peak is similar to that of ⁵D₀-⁷F₄(701 nm) transition peak in the emission spectra with the Judd-Ofelt theory.     

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.     

Luminescent properties of SrAl2O4: Eu,Dy material prepared by the gel method

SrAl₂O₄:Eu,Dy materials were first prepared by the gel method. Compared with samples prepared by solid state reactions, the grain size of the gel method is greatly reduced to nanometer grade. A clear blue shift occurs in the excitation and emission spectra of nano SrAl₂O₄:Eu,Dy, of which the peak of the excitation and emission spectra are at 323 and 500 nm respectively. The brightness of nano SrAl₂O₄:Eu,Dy is greatly reduced. The blue shift and the change of luminescent intensity in nano SrAl₂O₄:Eu,Dy materials can be attributed to the effect of surface energy.     

A single-phase white-emitting La10(SiO4)6O3：Eu2+/Eu3+ phosphor for near-UV LED-based application

A novel single-phase white-emitting phosphor La₁₀(SiO₄)₆O₃ (LSO): xEu has been synthesized by high-temperature solid-state reaction. Its crystal structure, luminescence properties, fluorescence decay time and oxygen vacancies have been characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. XRD result shows a typical oxyapatite structure with the space group of P6₃/m. Characteristic excitation and emission peaks of Eu²⁺ and Eu³⁺ were observed from PL studies. The optimum doping concentration of Eu was found to be 7.5 mol% (x = 0.075). In this work, the lifetimes of Eu³⁺ and Eu²⁺ were considerably longer than those from some references. Under the excitation of different near ultraviolet (n-UV) longer wavelengths (λex = 360, 370, and 380 nm), the white light emission can be realized with the CIE chromaticity coordinates (0.3907, 0.3595), (0.3472, 0.3282), and (0.3504, 0.3062) for the phosphor LSO: 0.075Eu. The chromaticity coordinates of the phosphor were all located in the white region. Therefore, it is suggested that the explored LSO: 0.075Eu phosphor can be a good candidate for white light-emitting diodes (W-LEDs) application.     

Effects of Er3+ and/or Cr3+ doping on crystallization activation energy and fluorescence properties of transparent ZnGa2O4 glass-ceramics

Er³⁺ and/or Cr³⁺ doped transparent ZnGa₂O₄ glass-ceramics were successfully obtained by one-step heat treatment. The results showed that Er³⁺ ions can enrich around ZnGa₂O₄ crystal to reduce the crystallization activation energy and promote the growth of ZnGa₂O₄ crystal. Cr³⁺ ions may successfully occupy the Ga³⁺ sites in the ZnGa₂O₄ lattice but will increase crystallization activation energy and inhibit the growth of the ZnGa₂O₄ crystal. Before and after crystallization, the coordination-field intensity of Cr³⁺ ions increased from 2.17 to 2.86, resulting in the peak position of its emission spectra moving from 850 to 688 nm. By excitation at 378 nm, the precursor glass co-doped with Er³⁺ and Cr³⁺ ions only showed the characteristic emission peaks belonging to Er³⁺ ions. After heat treatment, the characteristic emission peaks belonging to Er³⁺ and Cr³⁺ ions existed simultaneously, and the emission color changed from green to yellow. By excitation at 980 nm, there were only characteristic emission peaks belonging to Er³⁺ ions of the Er³⁺/Cr³⁺ co-doped glasses before and after heat treatment. The results showed that the Er³⁺ and/or Cr³⁺ doped ZnGa₂O₄ glass-ceramics have adjustable luminescence ability and show potential application value in the field of luminescence display.     

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.     

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.     

Unusual concentration induced antithermal quenching of the Eu2+ emission at 490 nm in Sr4Al14O25:Eu2+ for near ultraviolet excited white LEDs

Thermal quenching of phosphor is an important challenge for its practical application in phosphor-converted white light-emitting diodes (pc-WLEDs) and it usually becomes aggravated with the increase of activator concentration. Conversely, this work finds the thermal quenching of Eu²⁺ emission at 490 nm in Sr₄Al₁₄O₂₅:Eu²⁺ does not follow this in the temperature range of 300 to 480 K, and the rate of it is even slowed down as the concentration of Eu²⁺ increases. However, at the same time, the experiment on three heating-cooling cycles of Sr₄Al₁₄O₂₅:Eu²⁺ reveals that the thermal degradation of Eu²⁺ emission becomes improved. Once Eu²⁺ ions are doped into Sr₄Al₁₄O₂₅, they will prefer substituting for the 10- and 7-coordinated strontium sites Sr1 and Sr2, respectively. The emission centers Eu1 and Eu2, therefore, appear. The abnormal phenomenon is perhaps partly due to the enhanced energy transfer from the emission center Eu1 at 407 nm to the one Eu2 at 490 nm. It is also found interesting that the introduction of AlN can enhance the emission of Sr₄Al₁₄O₂₅:Eu²⁺ without leading to the deterioration of thermal degradation. In the end, a prototype of pc-WLED was fabricated with Sr₄Al₁₄O₂₅:Eu²⁺ to demonstrate the application of white lighting. This work is not only beneficial to the understanding of the relationship between concentration and thermal quenching, but also conducive to the design of the heavily doped phosphor for WLEDs with better resistance to thermal quenching.     

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     

Tunable luminescence properties and efficient energy transfer in Eu,Mn co-doped Ba2MgP4O13

A series of Ba₂Mg_1−xMn_xP₄O₁₃ (x = 0-1.0) and Ba_1.94Eu_0.06Mg_1−xMn_xP₄O₁₃ (x = 0-0.15) phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), the photoluminescence spectra, and the decay curves are investigated. XRD analysis shows that the maximum tolerable substitution of Mn²⁺ for Mg is about 50 mol% in Ba₂MgP₄O₁₃. Mn²⁺-singly doped Ba₂MgP₄O₁₃ shows weak red-luminescence peaked at about 615 nm. The Eu²⁺/Mn²⁺ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 430 nm originating from Eu²⁺ and a broad red-emitting one peaked at 615 nm from Mn²⁺ ions. The luminescence of Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ in Ba₂MgP₄O₁₃. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. The emission colors could be tuned from the blue to the red-purple and eventually to the deep red. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism is supported by the decay lifetime data. The energy transfer efficiency and the critical distance are calculated and discussed. The temperature dependent luminescence spectra of the Eu²⁺/Mn²⁺ co-doped phosphor show a good thermal stability on quenching effect.     

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB₂O₄, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB₂O₄ host lattice are studied for various beta doses ranging from 0.1 to 10?Gy. The high-temperature peak of Eu activated sample located at 192?°C exhibited a linear dose response in the range of 0.1–10?Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB₂O₄ were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu³⁺ ions located at 576–710?nm assigned to the ⁵D₀→⁷F_J (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ was reached Eu³⁺ concentration of 5?mol%; quenching occurred at higher concentrations. Strong emission peak for Eu³⁺ ions at 614?nm with transition ⁵D₀→⁷F₂ is observed. The CL experimental data indicate that ZnB₂O₄:Eu³⁺ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.     

Phase formation and spectral evolution of (Sr,Ba)2Si(O,N)4:Eu2+ phosphors

Sr_2‐xBa_xSi(O,N)₄:Eu²⁺ (SB_xSON:Eu²⁺) oxynitridosilicate phosphors were prepared via incorporation of N^3?, Eu²⁺, and Ba²⁺ ions into Sr₂SiO₄ (SSO) lattices. X‐ray diffraction patterns of the prepared powders revealed that SB_xSON:Eu²⁺ was a solid‐solution form of SSO. An increase in x values caused a phase transition and an expansion of the unit cell. The photoluminescence excitation (PLE) spectra of SB_xSON:Eu²⁺ were broad, covering the ultraviolet range to the visible range. Corresponding PL emission spectra strongly depended on the excitation wavelengths and consisted of two emission bands, one in the green‐blue region (A‐band) and the other in the red region (B‐band), which were assigned to Eu(I) and Eu(II), respectively. The B‐band resulted from a dramatic red‐shift of the green emission band assigned to Eu(II) of SSO:Eu²⁺, revealing that the nitridation process preferentially affected the Eu(II) sites. This behavior was explained by crystal field splitting, the fluorescence decay time, and thermal quenching. The Ba²⁺ substitution caused evolution of the PL spectra, and its effects on the spectra were discussed under consideration of ionic size and covalence.     

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.     

Structure and Luminescence Characteristics of Eu3+‐Activated Trigonal Layered Perovskite Ba2La2ZnW2O12

Eu³⁺‐doped tungstate Ba₂La₂ZnW₂O₁₂ phosphors with perovskite‐structure were prepared by the high temperature solid‐state reaction. The X‐ray powder diffraction (XRD) patterns and structure refinements indicate that the phosphors crystalized in the trigonal layer‐perovskite. The luminescence properties of the phosphors were investigated such as photoluminescence (PL) excitation and emission spectra, decay lifetimes, and color coordinates. It was found that the pure host shows self‐activated emission excited by the UV light. Moreover, Ba₂La₂ZnW₂O₁₂ also shows scintillation characteristics under the X‐ray irradiation. The near‐UV and blue light can efficiently excite Eu³⁺‐doped Ba₂La₂ZnW₂O₁₂ phosphors inducing the strong orange–red luminescence. The optimal Eu³⁺ doping concentration in this host is 40 mol%. The luminescence spectra and the luminescence color of the phosphors strongly depend on the doping levels and excitation wavelength. The different luminescence features were discussed on the base of crystal structure. Eu³⁺ ions have two possible substitutions on A or B sites in this trigonal layered perovskite. The phosphor could act as a candidate for the potential application in near‐UV excited white‐LEDs lighting.     

Investigation of Eu2+ luminescence in barium tetraphosphate Ba3P4O13 polycrystalline ceramics

In this paper, Ba₃P₄O₁₃:Eu²⁺ phosphor was synthesized by a solid-state reaction. The photoluminescence (PL) emission spectrum and luminescence decay kinetics confirm that the doped Eu²⁺ ions can occupy two different Ba²⁺ sites. The PL excitation spectrum shows a broad band matching well with the emission of near-UV chip. Ba₃P₄O₁₃:Eu²⁺ is a promising phosphor for near-UV chip excited white LEDs. The doped Eu³⁺ ions can also be reduced to Eu²⁺ ions in air atmosphere at high temperature. Charge compensation mechanism is applied to explain this kind of abnormal reduction.