Intense single-band red upconversion emission in BiOCl:Er~(3+) layered semiconductor via co-doping Ho~(3+)

Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions(RE~(3+)) doped upconversion(UC) materials is still desirable.In this work,the intense single-band red emission is achieved by co-doping only Ho~(3+)in the BiOCl:Er~(3+) under 1550 nm excitation.In the BiOCl layered host,co-doping Ho~(3+)can further enhance the red emission and simultaneously suppress the green emission of Er~(3+),and thus obviously improve the red-to-green(R/G) ratio.It is found that Ho~(3+)does not se rve as ene rgy trapping through the ~5 I_6 state as in traditional UC materials but acts as ET bridge(~4 S_(3/2),~2 H_(11/2)(Er~(3+))→~5 F_4,~5 S_2(Ho~(3+))→~4 F_(9/2)(Er3+)).The tuning mechanism of Ho3+is discussed in detail and further confirms through a comparative experiment.Our research gives an unusual perspective to tune the UC behavior of Er3+through co-doping Ho~(3+),which might be inspiring for achievement of single-band red UC emission.     

Growth and property enhancement of Er3+-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystal

Er~(3+)-modified 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3-0.32 PbTiO_3(PMN-32 PT) single crystals were grown by using the flux method. The growth mechanism of the crystal and influences of Er~(3+) ions on phase structure,electrical and optical properties were investigated. Results reveal that the crystals are still pure perovskite structure with Er3+ ions doping, but lattice enlarges slightly. The coercive electric field is increased from 4.83 to 6.37 kV/cm for [100]-oriented crystals comparing to undoped PMN-32 PT single crystals.Moreover, the crystal exhibits upconversion emission properties. Green(531 and 552 nm) and red(670 nm) emission bands are recorded under the excitation of 980 nm diode laser, which correspond to the ~2 H_(11/2)→~4 I_(15/2), ~4 S_(3/2)→~4 I_(15/2) and ~4 F_(9/2)→~4 I_(15/2) transitions of Er~(3+) ions. Our results show the feasibility of using this crystal in photoelectric multifunctional devices.     

A tunable yellow emission from three-band emission of singly doped single-phased phosphor BaY_2S_4：Ho~（3＋）

The establishment of an approach to design tunable yellow emission through singly doped single-phased phosphors to obtain white LED-based InGaN chip was reported. BaY2-xS4:xHo3+ phosphors were prepared by the high temperature solid state reaction and characterized by X-ray diffraction and photoluminescence spectra. Under the excitation of 465 nm,the emission spectra of these phosphors exhibited three sharp emission lines peaked at about 492,543 and 661 nm of Ho3+ corresponding to 5F3,5F4 (5S2) and 5F5→5I8 t...     

Energy transfer and cross-relaxation induced multicolor upconversion emissions in Er~(3+)/Tm~(3+)/Yb~(3+) doped double perovskite La_2ZnTiO_6 phosphors

Investigation on the bright and stable upconversion(UC) phosphors with multicolor emissions is fundamental and significant for the frontier applications of display and tempe rature probe.He re,dive rse emitting colors with blue,cyan and yellowish green,which are caused by the energy transfer and crossrelaxation processes,are obtained by altering Er~(3+),Tm~(3+)and Yb~(3+) concentrations in Er~(3+)singly,Er~(3+)-Tm~(3+)-Yb~(3+)co-and tri-doped double perovskite La_2 ZnTiO_6(LZT) phosphors synthesized by a simple solid-state reaction.In addition,excellent infrared emission at 801 nm located at "first biological windo w" is collected in Tm~(3+)-Yb~(3+)co-doped phosphors.Meanwhile,the temperature sensing properties based on the thermally coupled levels(~2 H_(11/2)/~4S_(3/2)) of Er~(3+) ions were analyzed from 298 to 573 K of LZT:0.15 Er~(3+)/0.10 Yb~(3+)phosphor,demonstrating that the maximal sensitivity value is about56×10-4 K~(1-) at 448 K.All these results imply that this kind of UC material has potential applications in display,bioimaging and optical device.     

Spectroscopic investigations on Yb~(3+) doped and Pr~(3+)/Yb~(3+) codoped tellurite glasses for photonic applications

In this work we repo rt on structural and spect roscopic properties of Yb3+doped and Pr~(3+)/Yb~(3+)co-doped TeO_2-Bi_2 O_3-ZnO-Li_2 O-Nb_2 O_5(TBZLN) tellurite glasses.Bending and stretching modes of TeO_2 and Te-OH bond(strong and weak) were analysed from the deconvolution of observed Raman and FT-IR spectra.Based on the absorption measurements,the energy bands of Yb~(3+)and Pr~(3+)ions are assigned.The spectroscopic properties for the radiative transitions of Yb~(3+)and Pr~(3+)ions were reported using McCumber and Judd-Ofelt theories.Visible emission bands originating from ~3 P_1 and ~3 P_0 to lower lying levels of Pr~(3+)were registered under 447 nm excitation.The emission band around 1334 nm assigned to the Pr~3:~1 G_4→~3 H_5 was observed when excited at 980 nm.The stimulated emission cross-section(σ_(emi)(λ))and effective linewidth(Δλ_(eff)) for the ~3 P_1→~3 H_6,~3 P_1→~3 H_5,~3 P_0→~3 H_6,~3 P_0→~3 F_2,~3 P_1→~3 F_3,~3 P_1→~3 F_4,~3 P_0→~3 F_4 and ~1 G_4→~3 H_5 transitions of Pr~(3+)are reported.Upconversion luminescence in Pr~(3+)/Yb~(3+)codoped glass upon 980 nm excitation was measured.Possible resonant transfer processes between Yb~(3+)and Pr~(3+)ions are presented and discussed.The chromaticity co-ordinates were also evaluated from the visible emission spectra showing that Pr~(3+)/Yb~(3+)co-doped glass may be suitable for the development of yellow-orange(λ_(exc)=447 nm) and near white light(λ_(exc)=980 nm) emitting devices in photonics.     

Luminescence properties of calcium tungstate activated by lanthanide(Ⅲ) ions

Calcium tungstate phosphors activated by the Ln3+ ions(Ln=Pr, Nd, Tb, Yb) were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy(SEM), X-ray powders diffraction(XRD) and infrared spectra(FT-IR). The samples were found to show luminescence properties(down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb3+/Yb3+ showed green DC and UC luminescence characteristic of Tb(III) ion in the range of 470–660 nm, corresponding to the 5D4→7F6,5,4,3,2 electronic transition. CaWO4 doped with Pr3+/Yb3+ showed week blue, green and red(DC and UC) luminescence of Pr(III) ion, in the wavelength region of 450–700 nm. Emission peaks were ascribed to the 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3+/Yb3+ phosphor emitted orange UC luminescence at 450–690 nm(2P3/2→4I15/2, 4G7/2→4I9/2,11/2,13/2) and strong near-infrared UC luminescence at 720–900 nm(4F7/2+4S3/2→4I9/2, 4F5/2+2H3/2→4I9/2, 4F3/2→4I9/2) which is the characteristic of Nd(III) ion.     

Upconversion luminescence of KGd（MoO_4）_2：Er~（3＋）,Yb~（3＋） powder prepared by Pechini method

Er3+ doped potassium gadolinium molybdate (KGM) phosphor with sensitizer Yb3+ ion was synthesized by the Pechini method using citric acid and ethylene glycol. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC), which indicated that ultrafine uniform crystallites of KGM:Er,Yb were obtained by sintering the precursors at above 650 ℃ for 5 h. Upconversion luminescence (UL) spectra of the samples ...     

White up-conversion luminescence and highly-sensitive optical temperature sensing in Na3La(VO4)2:Yb,Er,Tm,Ho phosphors

In this work,tunable white up-conversion luminescence was achieved in the Yb³⁺,Er³⁺,Tm³⁺,Ho³⁺ codoped Na₃La(VO₄)₂ phosphors under 980 nm excitation.The emissions of three primary colors are mainly attributed to the ²H_11/2/⁴S_3/2→⁴I_15/2 transitions of Er³⁺,¹G₄→³H₆ transition of Tm³⁺,and_5...     

A novel synthesis method and up-conversion properties of hexagonal-phase NaYF4:Er nano-crystals

A novel synthesis method for hexagonal(β)-phase NaYF4:Er nano-crystals(NCs)which showed up-conversion(UC)from infrared to visible spectral region was developed.The NaYF4:Er NCs were synthesized in oleic acid(OA)and 1-octadecene(ODE)with Y2(CO3)3· xH2O,Er2(CO3)3· xH2O,Na2CO3 and NH4F as precursors.This proposed method was simple and less toxic compared with generally used method so far.The XRD results showed that the molar ratio of OA/ODE and the temperature were key factors for phase control of NaYF4:Er NCs.The UC emission spectra were obtained with the emission wavelength at about 980 nm(4I11/2→4I15/2),800 nm(4I9/2→4I15/2),660 nm(4F9/2→4I15/2)and 540 nm(4S3/2→4I15/2)from Er3+ ions,by excitation wavelength of 1550 nm.The slope values,n,in the pump-power dependence,showed that the emission at 980 and 800 nm were generated by 2-step UC and at 660 nm and 540 nm were 3-step UC.The optical process for the UC excitation was discussed.     

Synthesis,structure and optical properties of novel thermally robust Dy~(3+)-doped Ca_9Sc(PO_4)_7 phosphors for NUV-excited white LEDs

The powder samples of Ca₉Sc(PO₄)₇:xDy^{^(3+})white emitting phosphors were prepared via a solid state reaction technique.The Ca₉Sc(PO₄)₇:Dy³⁺samples were researched by using the GSAS Rietveld refinement and X-ray diffraction(XRD) methods,and SEM images and elemental maps were recorded.Under 350 nm excitatio n,the emission spectra of Ca₉Sc(PO₄)₇:xDy³⁺samples have two obvious peaks and one weak peak at 484,572 and660 nm,corresponding to the characteristic electron transitions of(⁴F_9/2→ ⁶H_15/2,blue),(⁴F_9/2→ ⁶H_13/2,yellow) and(⁴F_9/2→ 6 H11/2,red),respectively.The concentration quenching effect,decay lifetime and thermal quenching of the as-synthesized Ca₉Sc(PO₄)₇:Dy³⁺samples were researched systematically.The Ca₉Sc(PO₄)₇:0.02 Dy³⁺phosphor possesses a good thermal stability,of which the emission intensity at 423 K can maintain 79% of the initial value(273 K).In addition,through the study of the chro maticity coordinates of the Ca₉Sc(PO₄)₇:0.02 Dy³⁺phosphor,it is found that it is located in the white region,and the Commission Internationalede L’Eclairage(CIE) chromaticity coordinates are(0.339,0.389),The above results show that Ca₉Sc(PO₄)₇:xDy³⁺phosphors can be excellent candidate material for applications in NUV-excited white LEDs.     

Synthesis and optical properties of novel double perovskite Ca_2MgTeO_6:Dy~(3+),Na~+ phosphors for white LEDs

Novel yellow-emitting phosphors of Dy~(3+)-doped double perovskite Ca_2 MgTeO_6 were synthesized by using a conventional high-temperature solid-state reaction.The phase purity,particle morphology,size distribution,elemental composition,luminescence properties,and luminescence decay curves of the resulting products were then analyzed in detail.The Ca2 MgTeO_6:Dy~(3+),Na~+ phosphors show three emission peaks after near-ultraviolet excitation at 350 nm,which correspond to ~4 F_(9/2)→~6 H_(11/2),~4 F_(9/2)→~6 H_(13/2),and ~4 F_(9/2)→~6 H_(13/2) transitions,respectively.Among them,the strongest peak is observed at 573 nm.The best doping content of Dy~(3+)in Ca_2 MgTeO_6:xDy~(3+),xNa~+ phosphors is x=5 mol%.The calculated critical distance of energy transfer between Dy~(3+) ions is 1.6 nm.Luminescence quenching is confirmed to be due to dipole-dipole interactions among Dy~(3+) ions.The phosphors show excellent thermal stability with high activation energy(0.27 eV).The Commission Internationale de l'Eclairage(CIE) chromaticity coordinates of the Ca_2 MgTeO_6 Dy~(3+),Na~+ phosphors are located in the yellow region.White light-emitting diodes(w-LEDs) were fabricated with a high color rendering index(R_a) of 88 and a good correlated color temperature(CCT) of 5440 K.All observed properties indicate that Ca_2 MgTeO_6:Dy~(3+),Na~+ phosphors have potential applications in display and photonic devices.     

Structural and optical properties of Dy~(3+):YAlO_3 phosphors for yellow light-emitting diode applications

The spectroscopic properties of a series of Dy~(3+) single-doped and Dy~(3+)/Nd~(3+),Dy~(3+)/Tb~(3+),and Dy~(3+)/Tm~(3+)co-doped YAlO_3(yttrium aluminum perovskite,YAP) phosphors were investigated and compared through the measurements of optical absorption,emission spectra,and fluorescence decay curves.For the Dy~(3+) ion single-doped samples,the intensity of each absorption band increases with an increment in Dy~(3+) ion doping concentration,and the identified strong absorption peak at 447 nm indicates that Dy~(3+):YAP phosphors are suitable to be pumped by a blue laser diode(LD).For all co-doped samples,absorption peaks of Dy~(3+) ion along with some of the absorption bands of Nd~(3+),Tb~(3+),and Tm~(3+) ions are observed.Under 351 and 447 nm excitation,a prominent emission peak at 572 nm was obtained in all the samples,corresponding to Dy~(3+):~4 F_(9/2)→~6 H_(13/2) transition.Here,2 at% Dy~(3+):YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping.Among the three kinds of Dy~(3+) co-doped phosphors,Dy~(3+)/Tb~(3+):YAP phosphor possesses the dominant yellow emission.The fluorescence decay curves show exponential behaviour and are fitted well.The Commission International de L'Eclairage(CIE)chromaticity coordinates were calculated following the respective emission spectra,and it is found that all the coordinates locate in the yellow region.The energy transfer(ET) processes were investigated and the concentration quenching mechanism was discussed.The obtained results suggest that Dy~(3+)-activated YAP phosphors are good candidates for yellow LED applications.     

Plasmonic enhancement of upconversion emission in Ag@NaYF4:Er3+/Yb3+ phosphor

In this article upconversion luminescence of silver nanoparticles(AgNPs) coated NaYF_4:Er~(3+)/Yb~(3+)phosphor nano-particles was investigated.The prepared samples were characterized through various techniques.The surface plasmon band is observed for prepared AgNPs by analyzing UV-vis measurements and is used to enhance the upconversion emission.From the upconversion measurement the emission bands are observed at 522,546,and 656 nm corresponding to the ~2 H_(11/2)→ 4~1_(15/2),~4 S_(3/2)→~4 I_(15/2)and ~4 F_(9/2)→~4 I_(15/2) levels,respectively.The upconversion emission intensity of the above bands is found to enhance for sample containing 1 mmol AgNPs.Decay time of ~4 S_(3/2) and 4~F_(9/2) levels is found to decrease on coating of AgNPs and hence intensity enhancement is assumed due to the surface plasmon resonance(SPR) effect.     

Color tunable and white light emitting via energy transfer in single-phase BiOCl:Er3+,Sm3+ phosphors for WLEDs

BiOCl crystal shows potential as efficient optical host due to its special layered structure. Here,the luminescence properties of the Er~(3+)/Sm~(3+) co-doped BiOCl phosphors as single-phase phosphors were reported. Upon near ultraviolet excitation(NUV, 380 nm corresponding the ~4 I_(15/2)→ ~4 G_(11/2) transition of Er~(3+) ions), the phosphors exhibit the efficient characteristic emissions of Er~(3+) and Sm~(3+) ions simultaneously. The energy transfer(ET) from Er~(3+) to Sm~(3+) ions in the layered crystals has been validated by the variation of emission intensities and decay lifetimes respectively, which is ascribed to be a dipoledipole interaction. By virtue of the ET behavior and increasing Sm~(3+) ion concentration, the enhancing emission intensity of Sm~(3+) and the tunability of emission color from yellowish-green(0.318, 0.420) to white(0.343, 0.347) are realized. The results of our work indicate that the Er~(3+)/Sm~(3+) co-doped BiOCI phosphor has a promising application serving as single component white emitting phosphors for NUV excited WLEDs.     

Effects of annealing temperature and neodymium concentration on structural and photoluminescence properties of Nd~(3+)-doped Y_2O_3-SiO_2 powders

We report the structural and photoluminescence(PL) properties of Nd~(3+)-doped Y_2 O_3-SiO_2 powders(Y_2 O_3-SiO_2:Nd~(3+)) as functions of annealing temperature and Nd~(3+) ion doping concentration.Y_2 O_3-SiO_2:Nd~(3+)powders were prepared using the high-energy ball-milling(HEBM) method,and their structural and PL properties were investigated using X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,and PL spectroscopy.The XRD results reveal a cubic phase without impurities,and the peak broadening decreases with an increase in annealing temperature due to the increase in the crystallite size.The PL emission intensity increases with an increase in annealing temperature.The highest PL emission intensity is observed for the 300-min milled mixture annealed at 1000℃ for 1 h with a Nd~(3+) concentration of 1 mol%.The PL peaks excited by 800 nm radiation were detected,centered at 1080 nm(~4 F_(3/2)→~4 I_(11/2)) and 1350 nm(~4 F_(3/2)→~4 I_(13/2)).     

Synthesis of well oil-dispersible BaYF5:Yb3+/Er3+ nanocrystals with green upconversion fluorescence

Nearly monodisperse, regular-shaped and well oil-dispersible tetragonal BaYF₅:0.2Yb³⁺/0.02Er³⁺ nanocrystals (NCs) were synthesized in water-ethanol-oleic acid-sodium oleate system. The as-obtained NCs exhibited bright upconversion (UC) fluorescence under the 980 nm excitation. Blue (²H_9/2-⁴I_15/2), green ((²H_11/2, ⁴S_3/2)-⁴I_15/2) and red (⁴F_9/2-⁴I_15/2) transitions were observed. The results indicated that the relative intensity of green to red increased gradually with increasing power density, which were seldom in the previous work. Therefore, the UC properties and mechanism were studied in detail.     

Structure,Upconversion and Fluorescence Properties of Er3+-Doped TeO2-TiO2-La2O3 Tellurite Glass

Tellurite glasses were generally applied in rare earth optical materials due to their excellent physical and chemical properties. In this study, novel tellurite glasses composed of TeO₂-TiO₂-La₂O₃ were prepared by conventional melting-quenching method. Some basic physical parameters such as density, refractive indices, transition temperature and crystalline temperature were measured. The structure was analyzed by Raman spectra. The absorption, upconversion and fluorescence spectra were measured by UV-Vis-NIR spectrophotometer and spectrofluorimeter. Under 980 nm laser excitation, upconversion luminescence centered at 531, 545 and 657 nm corresponding to the transition ⁴H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 respectively, were observed. The effects of TiO₂ concentration on structure and upconversion luminescence intensity were discussed. The result indicated that the upconversion intensity increased as the phonon concentration decreased. The fluorescence properties of Er³⁺ doped glass were also studied. The dominant peak centered at 1531 nm and full width at half maximum (FWHM) was 64 nm. The Er³⁺ stimulated emission cross-section was calculated on the basis of McCumber theory. The possible mechanism of upconvesion and fluorescence were proposed.     

Green up-conversion luminescence in Yb^3＋-Pr^3＋ co-doped BaRE2ZnO5（RE=Y,Gd）

Yb3＋and Pr3＋co-doped BaRE2 ZnO5（RE=Y,Gd） up-conversion（UC） phosphors were successfully synthesized by a modified sol-gel method.The processing parameters and optimal concentration of Pr3＋and Yb3＋were determined.The structures and luminescent properties of samples were characterized by X-ray diffraction（XRD） and photoluminescence spectra（PL）.With the excitation of 980 nm laser diode,UC spectra showed five prominent emission bands centered at 484,514,546,656 and 670 nm,which were attributed to the1I6 →3H4,3P1 →3H4,3P0 →3H5,3P0 →3F2 and3P0 →3F3 transitions of Pr3＋,respectively.In the light of the pump power dependence,the possible UC mechanism in Yb3＋and Pr3＋co-doped BaRE2 ZnO5（RE=Y,Gd） was proposed and discussed.     

Upconversion emission of SrYbF5：Er3＋nanosheets modified by Tm3＋ions

Through a hydrothermal route, the Er3＋and Tm3＋co-doped SrYbF5 nanosheets were synthesized. The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and luminescence spec-tra. Under the excitation of 980 nm laser irradiation, the upconversion emissions of Tm3＋ions centered at 474 nm （1G4→3H6）, 679 nm （3F2→3H6）, 699 nm （3F3→3H6）, 803 nm （3H4→3H6） and emissions of Er3＋ions centered at 522 nm （2H11/2→4I15/2）, 543 nm （4S3/2→4I15/2）, 654 nm （4F9/2→4I15/2） were observed. The upconversion emissions of Er3＋ions were adjusted by the concentration of Tm3＋ions. The energy transfer mechanisms among Er3＋-Yb3＋-Tm3＋in SrYbF5 nanosheets were discussed.     

Zirconium metal organic framework for design of tetragonal rare earth-doped zirconia nanoparticles

Zirconium metal–organic frameworks ZrOBDC (where BDC = C₆H₄(COOH)₂, terephthalic acid) doped and co-doped with rare earth ions Ln (ZrOBDC:Ln³⁺, where Ln³⁺ = Eu³⁺ and Tb³⁺ as well as Er³⁺ and Yb³⁺) were used as precursors for the design of tetragonal rare earth doped zirconia nanoparticles (t-ZrO₂:Ln³⁺ NPs) through annealing process. Preparation, characterization and luminescence properties of ZrOBDC:Ln³⁺ and ZrO₂:Ln³⁺ NPs were investigated. The as-obtained t-ZrO₂:Ln³⁺ NPs have high purity with an average size of 20–30 nm. The luminescence spectra of ZrOBDC:Tb³⁺ and ZrOBDC:Eu³⁺ display strong green and red emission at around 544 and 611 nm which correspond to ⁵D₄ → ⁷F₅ and ⁵D₀ → ⁷F₂ transitions of Tb³⁺ and Eu³⁺ ions, respectively. The green and red up-conversion emissions of ZrO₂:Er³⁺,Yb³⁺ NPs due to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions are observed under 976 nm laser excitation.