Multi-site occupancies and dependent photoluminescence of Ca_(9)Mg_(1.5)(PO_(4))_(7):Eu^(2+) phosphors:A bifunctional platform for optical thermometer and plant growth lighting

Herein,we demonstrate an optical thermometer based on single Eu^(2+)doped Ca_(9)Mg_(1.5)(PO_4)_7 phosphors,which were prepared by traditional solid-state reaction technique under a reduction atmosphere.Considerations on the bond length obtained by the crystal structure refinement and the dependent photoluminescence performances allow to assign the two distinct emission bands to Eu^(2+)ions occupied Cal-Ca3 and Mg2 sites.Moreover,the blue and red emitting bands perfectly match with the photosynthetic action spectrum,which can enhance the indoor plant photosynthesis.The optimal doping content of Eu^(2+)ions in this Ca_(9)Mg_(1.5)(PO_(4))_(7)system is 3 mol%.The corresponding concentration quenching effect is verified as dipole-dipole interaction with the critical distance of 3.315 nm.Furthermore,by exploiting the fluorescence intensity technique,the optical thermal resistance properties of Ca_(9)Mg_(1.5)(PO_4)_7:Eu^(2+)are identified based on the temperature dependent emission spectra in a range of 303-523 K.In detail,the maximum absolute and relative sensitivity S_(a)and S_(r)of Ca_9Mg_(1.5)(PO_(4))_(7):Eu^(2+)thermometer are as high as 0.637%/K and 0.3155 K^(-1),respectively.Consequently,the Eu^(2+)doped Ca_(9)Mg_(1.5)(PO_(4))_(7)phosphors establish a bifunctional platfo rm for both optical the rmometer and plant growth lighting via multi-site occupancies.

Structure and luminescence properties of color-tunable phosphor Sr_(2)La_(3)(SiO_(4))_(3)F:Tb^(3+),Sm^(3+)

A series of single-phase and color-tunable phosphors Sr_(2)La_(3)(SiO_(4))_(3)F:0.15Tb^(3+),xSm^(3+)(SLSOF:0.15Tb^(3+),xSm^(3+)) was prepared using solid-state route.The X-ray diffraction(XRD) was used to characterize the phase of the as-prepared samples.The synthesized phosphors have apatite-type structure without other impurities.Sm^(3+) and Tb^(3+) ions substitute La^(3+) into the lattice and form a single-phase solid solution.The elements are evenly distributed in the sample according to the scanning electron microscopy(SEM) results.The crystal structure of the host phosphor was refined by the Rietveld method.The optical properties were studied in detail by investigation of the luminescence and diffuse spectra,fluorescence decay curves and energy transfer efficiency.The phosphor color can be changed from green(0.29,0.48) to yellow/orange and red(0.57,0.42) via adjusting the doping ratio of Sm^(3+).The SLSOF:0.15Tb^(3+),xSm^(3+)phosphors can emit typical multicolor light such as green,yellow,orange and red with gradually increasing Sm^(3+)doping concentration.All results indicate the occurrence of the energy transfer which results in the color-tunable properties of the phosphors.

Metal halide perovskite nanocrystals with enhanced photoluminescence and stability toward anti-counterfeiting highperformance flexible fibers

As a new type of light-collecting and luminescent material,all-inorganic cesium lead halide CsPbX_(3)(X=Cl,Br,I)perovskite nanocrystals(NCs)are expected to have a wide range of applications in the fields of photovoltaics,optoelectronics,and fluorescence anti-counterfeiting,etc.Therefore,improving the fluorescence performance and stability of CsPbX_(3)perovskite NCs to prompt their applications would promise both fundamental and practical significance for in-depth research in the field of halide perovskites.In this paper,we developed a modification strategy to introduce a halogen source,zinc bromide(ZnBr_(2))in hexane,to CsPbX_(3)perovskite that can be conducted under atmospheric conditions with reduced reaction cost and easier operation.The first work in this paper was to apply the modification strategy to CsPbI_(3)nanowires(NWs).Compared with the untreated NWs,the ZnBr_(2)/hexane modified CsPbI_(3)NWs exhibited better fluorescence properties.Subsequently,based on the study of perovskite NWs,we investigated perovskite nanocrystal-CsPbI_(3)nanorods(NRs)with different morphologies and sizes.It was found that the luminescence properties of nanorods(NRs)were superior.Later,we infiltrated the modified NRs into the aramid/polyphenylene sulfide(ACFs/PPS)composite paper yielded from our previous work to study its fluorescence performance for anti-counterfeiting.Their luminescence properties under ultraviolet light irradiation enable better performance in fluorescence anti-counterfeiting.The ZnBr_(2)/hexane modification strategy and the applications studied in this work will expand the scope of perovskite research,laying the foundation for the applications of fluorescent anti-counterfeiting,nano-photoelectric devices,and fluorescent composite materials.

Effective regulation of electronic structures and luminescence properties of LiGd_(9)(SiO_(4))6-x(GeO_(4))xO_(2):Dy^(3+)phosphors by tetrahedral substitution

A series of Dy^(3+)-activated phosphors with the general formula LiGd_(9)(SiO_(4))6-x(GeO_(4))xO_(2):Dy^(3+)(0≤x≤3)characterized by an apatite-type structure were successfully synthesized via a simple solid-state technique involving a partial substitution of[SiO_(4)]^(4-)with[GeO_(4)]^(4-)species.The effects of homovalent[GeO_(4)]^(4-)-[SiO_(4)]^(4-)substitution on the crystal structure,electronic structure,luminescence properties and thermal performance of LiGd_(9)(SiO_(4))6-x(GeO_(4))xO_(2):Dy^(3+)phosphors were studied in details.The phases and microstructure were performed by using X-ray diffraction(XRD)Rietveld refinement method and scanning electron microscopy(SEM)characterization.The substitution of smaller[SiO_(4)]^(4-)ions by larger[GeO_(4)]^(4-)ones makes their unit cell parameters increase gradually,and their band gaps decrease.The photoluminescence spectra of LiGd_(9)(SiO_(4))6-x(GeO_(4))xO_(2):Dy^(3+)(0≤x≤3)exhibit obvious emission peaks located at 477,573 and 675 nm within a visible wavelength region,resulting in an excellent white light.Furthermore,the I573nm/I477nm values of LiGd_(9)(SiO_(4))6-x(GeO_(4))xO_(2):Dy^(3+)(0≤x≤3)become larger with the partial substitution of[SiO_(4)]^(4-)by[GeO_(4)]^(4-),and their CIE chromaticity coordinates exhibit a yellow shift.

Synthesis and luminescence properties of apatite-type red-emitting Ba_(2)La_(8)(GeO_(4))_(6)O_(2):Eu^(3+)phosphors

A new kind of apatite-type red-emitting Ba_(2)La_(8)(GeO_(4))_(6)O_(2):Eu^(3+)phosphor was prepared by high temperature solid-state method.The Rietveld analysis based on the powder diffraction data shows that Ba_(2)La_(8)(GeO_(4))_(6)O_(2):Eu^(3+)phosphors possess a pure apatite phase without any impurity.The emission spectrum of Ba_(2)La_(8)(GeO_(4))_(6)O_(2):Eu^(3+)phosphor consists of two bands,an orange emission band from 500 to 600 nm and a red emission band from 600 to 680 nm.By varying the amount of the doped europium ions from 0.02 to 0.14 mol,it is found that the luminescent properties of this rare earth phosphor are the best when the concentration of europium ion is 0.08 mol.The optimum concentration is eventually proved to be 0.08 mol.The Eu^(3+)doping dependent luminescence quenching can be further ascribed to dipole-quadrupole interactions.The quantum yield of Ba_(2)La_(7.92)(GeO_(4))_(6)O_(2):0.08 Eu^(3+)is 37.23%.The CIE analysis confirms a reddish emission in the near ultraviolet(n-UV)excitation.All these above properties of the phosphor can help in contribution of promoting white light-emitting diode.

Recent progress on lanthanide complexes/clay minerals hybrid luminescent materials

The unique luminescent performance of lanthanide complexes/clay minerals hybrid materials has been fascinating many researchers for recent decades.It not only retains the excellent luminescent characteristics of lanthanide complexes but also improves the poor stability of the complexes.In this article,we introduce the luminescence mechanism of lanthanide complexes and point out the necessity of their combination with clay minerals.After the analysis of the structure and interlayer environment differences of 1:1-type and 2:1-type clay minerals,the intercalation methods(covalent grafting and ion exchange)appropriate for different clay minerals are summarized with examples.Based on the luminescence characteristics of the hybrid materials,the applications of these materials as luminescent probes in recognition of specific metal cations and molecules,detection of pH value,and temperature are reviewed.Finally,the current problems in the preparation of lanthanide complexes/clay minerals hybrid luminescent materials and shortcomings that need improvement in their performance are analyzed,and the application prospect is forecast.

Influence of dysprosium concentration on sensitivity of luminescent thermometers of phosphors Ca_(9)Tb(PO_(4))_(5)(SiO_(4))F_(2)

Tb^(3+),Dy^(3+)-co-doped Ca_(9)Tb_(x)Dy_(1-x)(PO_(4))_(5)(SiO_(4))F_(2) phosphors were prepared via high-temperature solidphase reaction method and the potential application in optical temperature measurements due to their color-tunable property was investigated in detail.The photoluminescence emission(PL) and photoluminescence excitation(PLE) spectra results show that the as-prepared phosphors exhibit both Tb^(3+) and Dy^(3+) emissions at 546 nm(^(5)D_(4)-^(7)F_(5) transition of Tb^(3+)) and 587 nm(^(4)F_(9/2)-^(6)H_(13/2) transition of Dy^(3+)) upon 376 nm excitation,respectively.In addition,the fluorescence decay analysis shows that the lifetime of the Tb3+emission rapidly decreases,which confirms the energy transfer existence between Dy^(3+) and Tb^(3+).Under 376 nm excitation,the temperature dependence of the fluorescence intensity ratios for the dualmission bands peaked at 546 and 587 nm was studied in the temperature range from 303 to 573 K.The results show that with the increase of Dy^(3+) concentration,the relative sensitivity first increases and then decreases,what’s more,the maximum relative sensitivity is 3.142×10^(-3)%/K for Ca_(9)Tb_(x)Dy_(1-x)(PO_(4))_(5)(SiO_(4))F_(2)(x=0.4).As a consequence,this preliminary study provides a novel method for exploring the novel thermo meters.

A novel blue-purple Ce^(3+) doped whitlockite phosphor:Synthesis,crystal structure,and photoluminescence properties

At present,the rare earth(RE) ions doped phosphors have attracted more and more attention because of their excellent properties.In this paper,a series of novel blue-purple β-Ca_(3)(PO_(4))_(2):Ce^(3+) phosphors were synthesized by a high temperature solid phase method.The X-ray diffraction(XRD),infrared spectrum,energy dispersive spectroscopy(EDS),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),photoluminescence excitation and emission spectra were used to investigate the crystal structure,composition and the luminescent properties of the resulting samples.The phosphor shows a strong absorption in the ultraviolet band.Under the excitation of 269 nm,the phosphor emits a strong purple fluorescence ranging from 360 to 520 nm.When Ce^(3+) doping content is 0.07 mol,the strongest luminescence intensity is reached,and the concentration quenching mechanism is dipole-dipole(d-d)interaction for Ce^(3+) based on Dexter theory.

Effect of anionic group[SiO_(4)]^(4-)/[PO_(4)]^(3-) on the luminescence properties of Dy^(3+)-doped tungstate structural compounds

Novel scheelite structures of Li_(2)Ca(WO_(4))_(2),Li_(2)Ca_(2)(WO_(4))(SiO_(4)),and LiCa_(2)(WO_(4))(PO_(4))fluorescent materials were successfully prepared using a high-temperature solid-phase process.The compounds were characterized by X-ray diffraction and energy dispersive spectroscopy.The tests revealed that the substitution of[WO_(4)]^(2-)by[SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron in tungstate had no significant influence on the crystal structure of the Li_(2)Ca(WO_(4))_(2).When Dy^(3+) ions were introduced as an activator at an optimum doping concentration of 0.08 mol%,all of the as-prepared phosphors generated yellow light emissions,and the emission peak was located close to 576 nm.Replacing[WO_(4)]^(2-) with [SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron significantly increased the luminescence of the Li_(2)Ca(WO_(4))_(2) phosphors.Among them,the LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor had the best luminescence properties,decay life(r=0.049 ms),and thermal stability(87.8%).In addition,the as-prepared yellow Li_(2)Ca(WO_(4))_(2):0.08Dy^(3+),Li_(2)Ca_(2)(WO_(4))(SiO_(4)):0.08Dy^(3+),and LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor can be used to fabricate white light emitting diode(LED)devices.

Construction of SiO2-TiO2/g-C3N4 composite photocatalyst for hydrogen production and pollutant degradation: Insight into the effect of SiO2

Using low-cost precipitated silica(SiO2) as the carrier,a ternary SiO2-TiO2/g-C3N4 composite photocatalyst was prepared via the sol-gel method associated with a wet-grinding process.The asprepared composite exhibits photocatalytic hydrogen production and pollutant degradation performance under solar-like irradiation.The effect of SiO2 carrier on the properties of the heterostructure between TiO2 and g-C3N4(CN) was systematically studied.It is found that SiO2 has important effects on promoting the interaction between TiO2 and CN.The particle size of TiO2 and CN was obviously reduced during the calcination process due to the effects of SiO2.Especially,the TiO2 particles exhibit monodispersed state with particle size below 10 nm(quantum dots),resulting in the improvement of the contact area and the interaction betweenTiO2 and CN,and leading to the formation of efficient TiO2/CN Zscheme heterostructure in SiO2-TiO2/CN.Besides,the introduction of SiO2 can increase the specific surface area and light absorption of SiO2-TiO2/CN,further promoting the photocatalytic reaction.As expected,the optimum SiO2-TiO2/CN composite exhibits 12.3,3.1 and 2.9 times higher photocatalytic hydrogen production rate than that of SiO2-TiO2,CN and TiO2/CN under solar-like irradiation,while the photocatalytic active component in SiO2-TiO2/CN is only about 60 wt%.Moreover,the rhodamine B degradation rate of SiO2-TiO2/CN is also higher than that of SiO2-TiO2,CN and TiO2/CN.

Color tunable Ba0.79Al10.9O17.14∶xEu phosphor prepared in air via valence state control

A series of luminescent Ba0.79Al10.9O17.14∶xEu (x=0.005-0.12) phosphors were prepared by high-temperature solid-state reaction in air atmosphere.The coexistence of Eu2+ and Eu3+ was observed and verified by photoluminescence (PL) and photoluminescence excitation (PLE) spectra,X-ray photoelectron spectra (XPS),and diffuse reflection spectra.The band emission peaking at 430 nm was assigned to 4F65D-4F7 transition of Eu2+,and another four emissions peaking at 589,619,655,and 704 nm were attributed to 4F-4F transitions of 5D0-7FJ(J=1,2,3,4) of Eu3+.The related mechanism of self-reduction was discussed in detail.The color of the Ba0.79Al10.9O17.14∶xEu phosphors could be shifted from blue (0.23,0.10) to red (0.42,0.27) by doping Li+ ions,and the temperature dependence properties were investigated.