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.     

Effect of Li+ ion concentration on upconversion emission and temperature sensing behavior of La2O3:Er3+ phosphors

The effects of Li~+ co-doping concentration on the structure, upconversion luminescence and temperature sensing behavior of Er~(3+):La_2O_3 phosphors were investigated. X-ray diffraction and scanning electron microscopy observations reveal that Li~+ ion co-doping can change the lattice parameter of La_2O_3 host and increase the particle size of the samples. The optical investigation shows that co-doping of Li~+ ions can enhance the upconversion emission of Er~(3+) ions in La_2O_3 matrix effectively. Most importantly, the temperature sensing sensitivity of the samples is found to be dependent on Li~+ co-doping concentration,when the emission intensity ratio of the(~2H_(11/2)→~4 I_(15/2)) and(~4 S_(3/2)→~4 I_(15/2)) transitions of Er~(3+) is chosen as the thermometric index. Both of the optimum upconversion luminescence and temperature sensing sensitivity are obtained for 7 mol% Li~+ co-doped sample. When the Li~+ concentration is beyond 7 mol%,both the quenching in upconversion intensity and the degradation of temperature sensitivity are observed, which may be due to the serious distortion in local crystal field around Er~(3+) ions caused by the excess Li~+ ions.     

Er~(3+)-Yb~(3+)-Na~+:ZnWO_4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er³⁺/Yb³⁺/Na+:ZnWO₄ phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) analysis.The frequency upconversion(UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation.The effect of codoping in the Er³⁺:ZnWO₄ phosphors on the UC emission intensity was studied.The UC emission bands that are exhibited in the blue(490 nm),green(530,552 nm),red(668 nm) and NIR(800 nm) region correspond to the ⁴F_7/2→⁴I_15/2.²H_11/2,⁴S_3/2→⁴I_15/2,⁴F_9/2→⁴I_15/2 and ⁴I9/2→⁴I_15/2 transitions,respectively.The temperature sensing performance of the Er³⁺-Yb³⁺-Na+:ZnWO₄ phosphors was investigated based on the 2 H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 thermally coupled transitions of the Er³⁺ions.The photometric study was also carried out for the developed phosphors.     

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.     

Synthesis and upconversion luminescence properties of NaYF4：yb^3＋/Er^3＋ microspheres

Cubic NaYF4:yb3+(20%)/Er3+(1%) microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm exci-tation, ultraviolet (4G11/2→4I15/2), violet (2H9/2→4I15/2), grogn (4F7/2→4I15/2, 2H11/2→4I15/2, and 4S3/2→4I15/2), and red (4F9/2→4I15/2) upconversion fluorescence were observed. The number of laser photons absorbed in one upconversion excitation process, n, was determined to be 3.89, 1.61, 2.55, and 1.09 for the ultraviolet, violet, green, and red emissions, respectively. Obviously, n=3.89 indicated that a four-photon process was involved in populating the 4G11/2 state, and n=2.55 indicated that a three-photon process was involved in populating the 4F7/2/2H<11/2>4S3/2 levels. For the violet and red emissions, the population of the states 2H9/2 and 4F9/2 separately came from three-photon and two-photon proc-esses. The decrease of n was well explained by the mechanism of competition between linear decay and upconversion processes for the de-pletion of the intermediate excited states.     

Effect of BaF2 addition on luminescence properties of Er3+/Yb3+ co-doped phosphate glasses

Er~(3+)/Yb~(3+) co-doped phosphate glasses(P_2O_5-Al_2O_3-BaO-BaF_2-K_2O-Er_2O_3-Yb_2O_3) with varying BaF_2 content,were prepared by a conventional melt quenching technique and their spectroscopic properties were examined through the Raman, absorption, emission and decay measurements. Raman spectra(350-1400 cm~(-1)) of the Er~(3+)/Yb~(3+) co-doped phosphate glasses with varying BaF_2 content, were recorded upon laser excitation at 785 nm. Near infrared luminescence spectra were measured in the1400-1600 nm region under 970 nm diode laser excitation and characteristic band was observed at1533 nm corresponding to ~4Ⅰ_(13/2)→~4Ⅰ_(15/2) transition of Er~(3+) ion. The decay curves for the ~4Ⅰ_(13/2) level of Er~(3+)ion, were measured and the lifetime is found to decrease from 7.94 to 7.70 ms when BaF_2 content increases from 0 to 8 mol% and then increases up to 7.83 ms with further increase in BaF_2 content(12 mol%). The emission cross-section.lifetime and figure of merit for the ~4Ⅰ_(13/2)→~4Ⅰ_(15/2) transition of Er~(3+) ion were evaluated and compared to the other host matrices. The upconversion luminescence was measured and intense red emission was observed for all the studied samples.     

Upconversion luminescence of Y2O3：Er^3＋ ,Yb^3＋ nanoparticles prepared by a homogeneous precipitation method

Y2O3： Er^3＋, Yb^3＋ nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3：Er^3＋,Yb^3＋ nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to ^2H11/2,^4S3/2→^4I15/2 and ^4F9/2→^4I15/2 transitions of the ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were 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.     

Saturation effect of up-conversion luminescence from erbium-doped,silicatitania sol-gel powders

The intensity of the visible up-conversion luminescence could be limited by a saturation effect produced by increased pump power. Visible up-conversion luminescence was obtained in erbium doped,silica-titania sol gel powders under dynamical pumping at 1532 nm. The saturation effect was studied for erbium radiative transitions 2H9/2→4I15/2 (410 nm),2H11/2→4I15/2 (530 nm),4S3/2→4I15/2 (550 nm),2H9/2→4I13/2 (567 nm) and 4F9/2→4I15/2 (675 nm). The recorded up-conversion luminescence decreased when increasing ex...     

Physical,structural and optical studies on magnesium borate glasses doped with dysprosium ion

Intense visible emissions from dysprosium(Dy3+) ions doped glasses became prospective for diverse technological applications. In this paper, physical, optical and structural properties of magnesium borate glasses doped with varied concentrations of Dy_2 O_3 were examined. Such glasses were synthesised by melt quenching method and characterized at room temperature using several analytical techniques.Luminescence and absorption spectra(in the visible region) of as-quenched samples were used to evaluate the physical and optical properties. XRD pattern confims the amorphous state of as-quenched samples. The Fourier transform infrared(FTIR) spectra of glasses reveal various bonding vibrations assigned to different functional groups. UV-vis-NIR spectra disclose eight absorption bands accompanied by a band for hypersensitive transition positioned at 1260 nm(~6 H_(15/2)→~6 F_(11/2)). The values of direct and indirect optical energy band gap of the studied glasses are decreased with the increase of Dy~(3+) ion contents. The photoluminescence spectra of all glasses under the excitation of 380 nm display two prominent emission bands centred at 497 nm(~4 F_(9/2)→~6 H_(15/2), blue) and 587 nm(~4 F_(9/2) →~6 H_(13/2), green).The achieved intense luminescence from the proposed glass composition may be beneficial for solidstate laser applications.     

Enhanced ultraviolet upconversion in YF3：Yb^3＋/Tm^3＋ nanocrystals

Unusual intense infrared-to-ultraviolet upconversion luminescence was observed in YF3:Yb3+(20%)/Tm3+(1%) nanocrystals under 980 nm excitation. The intense ultraviolet emissions (1I6→3H6, 1I6→3F4, and 1D2→3H6) were affirmed arising from the excitation processes of five-photon and four-photon. In comparison with the bulk sample with the same chemical compositions, ultraviolet upconversion lumi-nescence of the nanocrystals was markedly enhanced. Spectral analysis indicated that the enhancement was attributed to the decrease of Judd-Ofelt parameter Ω2, which precluded the transition rate from 3F2 to 3F4, enhanced the energy transfer process and populated the 1D2 level: 3F2→3H6 (Tm3+): 3H4→1D2 (Tm3+).     

Spectroscopic investigations on Dy3+ ions doped zinc lead alumino borate glasses for photonic device applications

This paper presents the structural, optical absorption, photoluminescence (PL) and decay spectral properties of Dy~(3+)ions doped zinc lead alumino borate (ZPAB) glasses to elucidate their possible usage in photonic devices such as w-LEDs and lasers. A broad hump shown by the XRD spectrum recorded for an un-doped ZPAB glass confirms its non-crystalline nature. The Judd-Ofelt (J-O) intensity parameter evaluated from the measured oscillator strengths of the absorption spectral features were used to estimate various radiative parameters and also to understand the nature of bonding between Dy~(3+)ions and oxygen ligands. Under 350 nm excitation, the as-prepared glasses are exhibiting two emission bands~4F_(9/2)→~6H_(15/2)(blue),and~4F_(9/2)→~6H_(13/2)(yellow) at 483 and 575 nm,respectively. From the PL spectra,the Y/B ratio values, CIE chromaticity color coordinates and color correlated temperature (CCT) were evaluated. The experimental lifetimes measured from the decay profiles are decreasing with increase in Dy~(3+)ions concentration in these glasses which may be attributed to the cross-relaxation and nonradiative multiphonon relaxation process. Decay profiles observed for higher concentration were well fitted to Inokuti-Hirayama (I-H) model to understand the energy transfer process and subsequent decrease in experimental lifetimes. The higher values of radiative parameters, emission cross-sections,quantum efficiency, optical gain and gain band width suggest the suitability of 0.5 mol%of Dy~(3+) ions in these ZPAB glasses for the photonic device application.     

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.     

Synthesis and luminescence properties of Tb3+/Eu3+ co-doped GdAlO3 phosphors with enhanced red emission

The(Gd_(0.97-x)Eu_xTb_(0.03))AIO_3(x= 0.005-0.07) phosphors were synthesized by the co-precipitation method,using ammonium bicarbonate as a precipitant.The combined technologies of FT-IR,XRD,FESEM,PLE/PL and photo luminescence decay analysis were used to study the phase evolution,morphologies and luminescent properties.The phosphors with good dispersion exhibit strong vivid red emission located at 617 nm(~5 D_0-~7 F_2 transition of Eu~(3+)) under the optimal excitation wavelength of 275 nm(~4 f~8-4 f~75 d~1 transition of Tb~(3+),~8 S_(7/2)→6~I_J transition of Gd~(3+)).The presence of Gd~(3+) and Tb~(3+) excitation bands on the PLE spectra monitoring the Eu~(3+) emission directly gives an evidence of Tb~(3+) → Eu~(3+) and Gd~(3+) → Eu~(~(3+)) energy transfer,The emission intensity varies with the Eu~(3+) amount,and the quenching concentration is ～5 at% which is close to the calculated value.The quenching mechanism is determined to be the exchange reaction between Eu~(3+).The temperature-dependent PL analysis indicates that the best(Gd_(0.92)Eu_(0.05)Tb_(0.03))AlO_3 sample possesses good thermally stable properties.All the(Gd_(0.97-x)Eu_xTb_(0.03))AIO_3 phosphors in this work have similar CIE chromaticity coordinates and color temperatures,which are(0.65 ± 0.02,0.35 ± 0.02) and ～2558 K,respectively.Fluorescence decay analysis shows that the lifetime for～617 nm emission decreases with the content of Eu~(3+) and temperature increasing.Owing to the Tb~(3+)→ Eu~(3+) energy transfer,the luminescent properties of the(Gd_(0.92)Eu_(0.05)Tb_(0.03))AlO_3 phosphors are superior to the single Eu~(~(3+)) doped sample(Gd_(0.95)Eu_(0.05))AlO_3.As a result,the prepared phosphors may be widely used in solid-state display and light emitting devices.     

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.     

White light-emitting Ba0.05Sr0.95WO4:Tm3+ Dy3+ phosphors

Tm~(3+) and Dy~(3+) co-doped Ba_(0.05)Sr_(0.95)WO_4 phosphors were synthesized by a low temperature combustion method. The structures of the samples were SrWO_4 phase and were identified by X-ray diffraction. The surface topographies of Ba_(0.05)Sr_(0.91)WO_4:0.01 Tm~(3+) 0.03 Dy~(3+) were tested by scanning electron microscopy. The particles are ellipsoid, and their average diameter is approximately 0.5 μm. The emission spectra of Ba_(0.05)Sr_(0.95)WO_4:Tm~(3+) show a peak at 454 nm which belongs to the ~3 H_6→~1 D_2 transition of Tm~(3+), and the optimum doping concentration of Tm~(3+) ions was 0.01. The emission spectra of Ba_(0.05)Sr_(0.95)WO_4:Dy~(3+) consist of the ~4 F_(9/2)→~6 H_(13/2) dominant transition located at 573 nm, the weaker ~4 F_(9/_2→~6 H_(15/2) transition located at 478 and 485 nm. and the weakest ~4 F_(9/2)→~6 H_(11/2) transition located at660 nm, and the optimum doping concentration of Dy~(3+) ions was 0.05. A white light is achieved from Tm~(3+) and Dy~(3+) co-doped Ba_(0.05)Sr_(0.95)MoO_4 crystals excited at 352-366 nm. With the doping concentration of Tm~(3+) fixed at 0.01, the luminescence of Ba_(0.05)Sr_(0.95)MoO_4:Tm~(3+)Dy~(3+) is closest to standard white-light emissions when the concentration of Dy~(3+) is 0.03; the chromaticity coordinates are(0.321,0.347), and the color temperature is 6000 K.     

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.     

Upconversion multicolor tuning of NaY(WO4)2:Tb3+ with Eu3+ doping

A series of Tb~(3+) and Eu~(3+) co-doped NaY(WO_4)_2 phosphors were synthesized by hydrothermal reactions.The crystal structure,morphology,upconversion luminescent properties,the energy transfer from Tb~(3+) to Eu~(3+)ions and the ~5 D_4→ ~7 F_5 transition of the Tb~(3+) ion in NaY(WO_4)_2:Tb~(3+),Eu~(3+) phosphors were investigated in details.The results indicate that all the synthesized samples are of pure tetragonal phase NaY(WO_4)2.Furthermore,the micrometer-sized needle spheres and excellent dispersion of the particles are obtained by adding polyethylene glycol(PEG-2000) as the surfactant.Phosphors of NaY(WO_4)_2:Tb~(3+),Eu~(3+) exhibit the492 nm blue emission peak,546 nm green emission peak,595 nm orange emission peak and 616 nm red emission peak under 790 nm excitation.The energy transfer from Tb~(3+) to Eu~(3+) is a resonant transfer,in which electric dipole-dipole interaction plays a leading role.By adjusting the doping concentration of Eu~(3+) in NaY(WO_4)_2: 1.0 mol%Tb~(3+),xmol%Eu~(3+) phosphors,the emitting color of UC phosphors can be tuned from green to red.     

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...     

Synthesis and optical characterization of Eu2+,Tb3+-codoped Sr3Y(PO4)3 green phosphors

A series of Eu~(2+),Tb~(3+)-codoped Sr_3 Y(PO_4)_3(SYP) green phosphors were synthesized by hightemperature solid-state reaction. Several techniques, such as X-ray diffraction, UV-vis spectrum,and photoluminescence spectrum, were used to investigate the obtained phosphors. The present study investigates in detail photoluminescence excitation and emission properties, energy transfer between the two dopants, and effects of doping ions on optical band gap. SYP:0.05 Eu2+ phosphor shows an intense and broad excitation band ranging from 220 to 400 nm and exhibits a bright green emission band with CIE chromaticity coordinates(0.189, 0.359) under 350 nm excitation. Green emission of SYP:0.03 Tb3+ is intensified by codoping with Eu~(2+), and energy transfer mechanism between them is demonstrated to be a dipole-dipole interaction. Upon 350 nm excitation, SYP:Eu~(2+),Tb~(3+) phosphors exhibits two dominating bands peaking at 466 and 545 nm, which are assigned to 4 f~65 d~1→4 f~7 transition of Eu~(2+) ions and ~5 D_4→~7 F_5 transition of Tb~(3+) ions, respectively. Optimal doping concentrations of Eu~(2+) and Tb~(3+) in the SYP host are 5 mol% and 15 mol%, respectively. Results indicate that SYP:Eu~(2+),Tb~(3+) phosphors are potentially used as green-emitting phosphors for white light-emitting diodes.