UC/DC luminescence of Ho~(3+) doped pyrochlore structured La_(2(1–x))Yb_(2x)TiO_5 phosphor synthesized by sol-gel method

Ho~(3+) doped La_(2(1–x))Yb_(2x)TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho~(3+) activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band(CTB) between Ho~(3+) ions and the nearest neighboring O~(2–) ions at 250–280 nm and four sharp bands associated to f-f transitions of Ho~(3+) ions at 350–500 nm. Under the blue light excitation at 461 nm, Ho~(3+) ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm(blue, ~5F_3→I_8) and 663 nm(red, ~5F_5→~5I_8) in the up-conversion(UC) spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho~(3+) alone, whereas they were much different from the down-conversion(DC) luminescent samples. When x=7.5 mol.%–17.5 mol.%, the UC emission spectra of them dominated at 546 nm(green, ~5S_2, ~5F_4→~5I_8) and enhanced significantly with the dose of Yb~(3+) ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.     

Visible-light emission properties of α-TeO_2:Ho~(3+)/Yb~(3+)/Eu~(3+) nanoparticles via both up-and down-conversion modes

In this study,α-TeO_2:Ho~(3+)/Yb~(3+),α-TeO_2:Eu~(3+) and α-TeO_2:Ho~(3+)/Yb~(3+)/Eu~(3+) nanoparticles were prepared via a simple hydrothermal process.The up- and down-conversion properties of the as-prepared nanoparticles were tested at room temperature under a near-infrared photo source(980 nm) and UV-vis photo source,respectively.The results indicated that α-TeO_2 NPs were a kind of outstanding host material for both up- and down-conversion luminescence.The α-TeO_2:Ho~(3+)/Yb~(3+) nanoparticles showed sharp up-conversion emission at 545 and 660 nm under 980 nm excitation,ascribed to the ~5S_2→~5I_8 and ~5F_5→~5I_8(Ho~(3+)) transitions,and weaker down-conversion emission at 545 nm under 455 nm excitation,ascribed to the ~5S_2→~5I_8(Ro~(3+)) transitions.The α-TeO_2:Eu~(3+)nanoparticles showed strong down-conversion emission at 592 and 615 nm under 395 nm excitation,attributed to the ~5D_0→~7F_1 and~5D_0→~7F_2(Eu~(3+)) transitions.Possessing the advantages of these two luminescent materials,the as-prepared tri-doped samples ofα-TeO_2:0.5Ho~(3+)/10Yb~(3+)/3Eu~(3+)(mol.%) nanoparticles could successfully emit visible light via both up- and down-conversion modes.     

Enhanced 1.8 μm emission in Er~(3+)/Tm~(3+) co-doped lead silicate glasses under different excitations for near infrared laser

A detailed study of the fluorescence emission properties and energy transfer mechanism in Er~(3+)/Tm~(3+) co-doped lead silicate glasses was reported. Enhanced near infrared 1.8 μm and visible up-conversion emissions were investigated under 808 and 980 nm excitations, respectively. The energy transfer mechanism between Er~(3+) and Tm~(3+) was analyzed according to the absorption spectra, the emission spectra and the level structures of Er~(3+) and Tm~(3+). The energy transfer efficiency between Er~(3+) and Tm~(3+) reached 68.1% in the Er~(3+)/Tm~(3+) co-doped lead silicate glasses when pumped by 808 nm laser diode. Based on the absorption spectra, the Judd-Ofelt parameters, spontaneous emission probability, absorption and emission cross sections, gain coefficients were calculated and analyzed. It was found that the calculated emission cross section and the maximum gain coefficient around 1.8 μm were 4.9×10~(–21)cm~2 and 1.12 cm~(–1), respectively. These results indicated that the Er~(3+)/Tm~(3+) co-doped lead-silicate glasses had potential application in near infrared lasers.     

Photoluminescence properties of Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5Y_9F_(32)single crystal with high thermal stability for white light-emitting diodes

A novel Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes.The fluorescence spectra of various Sm~(3+)ion concentrations and fixed 0.4 mol% Tm~(3+) and 0.5 mol% Tb~(3+) were measured and studied systematically excited by near-ultraviolet light of 355 nm.The Sm3+ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands.A near pure white light emission with color coordinates(0.3295,0.3057) and color temperature(5657 K) can be obtained when the concentrations of Tm~(3+),Tb~(3+) and Sm~(3+) ions are 0.4 mol%,0.5 mol%and 0.8 mol%,respectively.Furthermore,the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%.The tri-doped Na_5 Y_9 F_(32) single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by～3% with the increase of temperature from 280 to 450 K.The present results demonstrate that the Tm~(3+)/Tb~(3+)/Sm~(3+)tri-doped Na_5 Y_9 F_(32) single crystal may provide a promising candidate for white light-emitting diodes,luminescent materials and fluorescent display devices.     

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.     

Combustion synthesis and enhanced 1.5 μm emission in Y_2O_3:Er~(3+) powders codoped with La~(3+) ions

Er~(3+) and La~(3+) codoped Y_2O_3 nanocrystalline powders were synthesized by gel combustion method and characterized with thermal analysis, X-ray diffraction(XRD), transmission electron microscopy(TEM), high-resolution TEM(HRTEM) techniques and fluorescence spectroscopy. After being calcined at 1200 oC, the(Y_(1–x) La_x)_2O_3:Er~(3+) powders were confirmed to be cubic Y_2O_3 phase with the crystalline grain size in the range of 20–40 nm. The Er~(3+) emission at 1.53 μm from the ~4I_(13/2)→~4I_(15/2) transition was observed, which was found to be enhanced by introducing La~(3+) ions. Such enhancement could be attributed to the adjustment of Er~(3+) ions' local environment by the codoping of La~(3+) ions, leading to the increased ground state absorption cross section of Er~(3+) ions.     

Photoluminescence properties of YAG:Ce~(3+),Pr~(3+) nano-sized phosphors synthesized by a modified co-precipitation method

Monophasic Ce~(3+) and Pr~(3+) co-doped yttrium aluminum garnet(YAG:Ce~(3+),Pr~(3+)) nanoparticles with good dispersity and uniform grain sizes in the range of 50–80 nm were prepared by a two-step route, which consisted of a modified co-precipitation preparation of mixed metal hydroxide hydrate intermediates at low temperature of about 40 oC and a subsequent calcination conversion of the synthesized intermediates to crystalline nanoparticle products at about 1000 oC. The influences of both the lanthanide ion(Ce~(3+) and Pr~(3+)) doping concentration and different doping(Ce~(3+)/Pr~(3+)) ratio on the photoluminescence intensity were systematically investigated. The synthesized (Ce_(0.6)Pr_(0.4))_(0.04)Y_(2.96)Al_5O_(12) nanoparticles were near spherical nanoclusters with good dispersity and uniform sizes in the range of 50–80 nm for about 85% of the particles. The strongest photoluminescence intensity was observed for the (Ce_(0.6)Pr_(0.4))_(0.04)Y_(2.96)Al_5O_(12) nanoparticle products.     

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.     

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.     

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)).     

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.     

Optical properties and Judd–Ofelt analysis of Nd2O3 nanocrystals embedded in polymethyl methacrylate

PMMA matrices were doped with nano-crystalline neodymium oxides synthesized by thermal decomposition process. X-ray diffraction and high-resolution transmission electron microscopy measurements were carried out to investigate the structure, phase, and the morphology of the Nd_2O_3 nanocrystals and those embedded in the PMMA matrix. The average grain sizes were estimated 35 ± 6 nm and 46 ± 4 nm for non-annealed and annealed Nd_2O_3 particles, respectively. The grain size distributions(GSD) were calculated from the diffraction peaks of the annealed and non-annealed Nd_2O_3 powders and doped PMMA samples. The mass density, refractive index. UV-Visible absorption spectra were measured and the data were analyzed using the Judd-Ofelt approach to determine the oscillator strengths, the spontaneous emission probabilities and the branching ratios as a function of the nano-crystalline Nd_2O_3 content in the range of 0.1 wt.%-20 wt.% of MMA. Luminescence spectra upon 808 nm diode laser excitation were carried out in the wavelength range of 850-1550 nm at room temperature. The photoluminescence study has shown that the reasonably sharp emission peaks were observed upon heat treatment at 800 ℃ for 24 h for all concentrations of Nd_2O_3 nanopowders in PMMA. The infrared laser transition of Nd~(3+) ions at about 1.06 μm due to the ~4F_(3/2)→~4I_(11/2) transition was analyzed and discussed in Nd_2O_3 system for their possible applications in the photonic technology.     

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.     

Crystal growth and spectral characterizations of Ho~(3+)-doped Li_3Ba_2La_3(MoO_4)_8 crystal

A large Ho~(3+):Li_3Ba_2La_3(MoO_4)_8 crystal with high optical quality and well-developed appearance was grown by the flux method. The main spectral properties of the crystal, including the absorption spectra, fluorescence spectra and fluorescence decay curves were recorded at room temperature. The Judd-Ofelt(J-O) theory was applied to calculate the oscillator strength parameters Ω_t(t=2, 4, 6), spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes of Ho~(3+) ions undergoing transitions from ground state ~5I_8 to the excited states. The stimulated emission cross-section for the ~5I_7→~5I_8 transition was estimated to be 1.32×10~(–20) cm~2 at 2045 nm by Fuchtbauer-Ladenburg(F-L) equation and the quantum efficiency of the ~5I_7 level was calculated to be 89%.     

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.     

Remarkable red-shift of upconversion luminescence and anti-ferromagnetic coupling in NaLuF_4:Yb~(3+)/Tm~(3+)/Gd~(3+)/Sm~(3+) bifunctional microcrystals

Lanthanide doped bifunctional materials are potentially important for developing multifunctional devices. Here, NaLuF_4:Yb~(3+)/Tm~(3+)/Gd~(3+)/Sm~(3+) optical-magnetic bifunctional microcrystals were successfully synthesized by hydrothermal method, which could emit ~480 nm blue light from the ~1G_4→~3H_6 electronic transition and ~800 nm infrared light from the ~3H_4→~3H_6 electronic transition of Tm~(3+) ion, under the excitation of 980 nm infrared light. By doping Sm~(3+) ion into Na Lu F4:Yb~(3+)/Tm~(3+)/Gd~(3+), the infrared emission peak centered at 800 nm would shift obviously to longer wavelength. This indicated that Sm~(3+) ion could efficiently tune the energy level gaps of Tm~(3+) ions in Na Lu F4 host which was demonstrated based on the crystal field theory. In addition, these NaLuF_4:Yb~(3+)/Tm~(3+)/Gd~(3+)/Sm~(3+) microcrystals presented unique ferromagnetic property instead of usually reported paramagnetic property. Importantly, the ferromagnetic property decreased with increasing the concentration of Gd~(3+) ion. This was in good agreement with Swift's theoretical investigation that the coexistence of light rare earth(Gd~(3+)) and heavy rare earth(Yb~(3+)/Tm~(3+)) would lead to the anti-ferromagnetic coupling in the sub-lattices.     

Spectroscopic analysis of trivalent Nd~(3+)/Yb~(3+) ions codoped in PZS host glasses as a new laser material at 1.06 μm

This paper reports on the spectral results of Nd~(3+)/Yb~(3+) ions codoped 50P_2O_5-30ZnO-20SrO(PZS, in mol.%) glasses which were prepared by a melting technique. The glass transition temperature and spectroscopic properties of these glasses were estimated. From the absorption spectra, Judd-Ofelt(J-O) intensity parameters(Wk), were calculated. Using J-O intensity parameters, several radiative properties such as spontaneous transition probabilities(AR), radiative branching ratios(bR) and radiative lifetimes(tR) were determined for the exciting levels of the Nd~(3+) ions. The large value of the stimulated integrated cross-section and the lifetimes of Nd~(3+) level revealed the potential of the present glasses as a candidate for generating laser emission at 1.06 μ m as continuous wave laser action and exploited for optical device fabrication. A broad emission band from 950 to 1100 nm was detected when the Nd~(3+)/Yb~(3+) was co-doped in PZS glasses excited by 805 nm lighting diode(LD). The energy transfer process from Nd~(3+)→Yb~(3+) in co-doped phosphate glasses was described in this paper.     

Upconversion luminescence of Y_2Ti_2O_7:Er~(3+) under 1550 and 980 nm excitation

Er~(3+) doped Y_2Ti_2O_7 phosphors were prepared by the high temperature solid state reaction method at 1500℃.X-ray diffraction and luminescence spectra were used to characterize the properties of samples.Due to the layer distribution of Y~(3+) ions in the pyrochlore Y_2Ti_2O_7 crystal,Er~(3+) ions,replacing Y~(3+) in Y_2Ti_2O_7 crystal,could realize high-concentration doping by suppressing energy migration between layers to minimize concentration quenching.Investigation on the upconversion characteristic of Y_2Ti_2O_7:Er~(3+)showed that the optimal doping concentration of Er~(3+) was up to 28 mol.%.Y_2Ti_2O_7:0.28 Er~(3+) exhibited both dominating red emission under 980 and 1550 nm excitation.The brightness of Y_2Ti_2O_7:0.28Er~(3+) were 4 times(980 nm) and 7 times(1550 nm) higher than that of Y_2Ti_2O_7:0.05Er~(3+).And Y_2Ti_2O_7:Er~(3+) presented much better red emission color purity and stability under 1550 nm excitation.     

Optical studies of Y_3(Al,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors obtained by the Pechini method

The Y3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+)(YAGG) nano-phosphors with homogeneous particle-size distribution,low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method.Only slight aggregation of the crystallites occurs after post-annealing at 1100℃.The intense Ce~(3+)bands in the excitation spectra of the Ce~(3+),Cr~(3+),Nd~(3+)co-doped materials monitoring the Cr~(3+) emission at 690 nm indicate energy transfer from Ce~(3+) to Cr~(3+).Weak Nd~(3+) lines are observed,as well.In addition,the emission of Nd~(3+)at 1060 nm with excitation of Ce~(3+) and Cr~(3+) confirms the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.The short average luminescence decay times for the Ce~(3+) emission indicate the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.Eventually,the Y_3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors exhibit persistent luminescence originating from the 4f~3→4f~3 transitions of Nd~(3+) which matches well to the first biological window to be used in bioimaging applications.     

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium(Eu~(3+)) doped glasses of chemical compositions(55-x)B_2O_3:10 SiO_2:25 Y_2O_3:10CaO:xEu_2O_3,where x denotes mol% and ranges 0≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique, Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu_2O_3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence,X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt(JO) intensity parameters(Ω_λ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability(A_R),branching ratio(β_R), stimulated cross section emission(σ) and radiative lifetime(τ_R) for ~5D_0→~7 F_J(J = 0,1,2,3 and 4) transitions. The decay rate of ~5D_0 fluorescent level for all the glass samples was single exponential. Lifetimes of the ~5D_0 level were decreased with increasing concentrations of Eu~(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates(x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu~(3+) doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.