Fluorescence Properties of Eu^(3+) Doped in Na_5Lu_9F_(32) Single Crystals

Eu^(3+) ion doped cubic Na_5Lu_9F_(32) single crystals with high quality were synthesized by a modified Bridgman method by using a high 70-90 ℃/cm temperature gradient for cross solid-liquid interface. The optical spectroscopic investigations of the obtained single crystal were reported for the absorption, excitation and emission. The experimental results show that a strong red emission at 609 nm attributing to the ~5D_0→~7F_2 transition of Eu^(3+) doped Na_5Lu_9F_(32) single crystals can be obtained under the excitation of 394 nm light and reach the maximum when the Eu^(3+) doping concentration is 4 mol% in present research. The local covalent is enhanced and symmetry is reduced with the increase of Eu^(3+) concentrations inferring from the strength parameters Ω_2 and Ω_4 calculated by their measured emission spectra. The CIE chromaticity coordinates of the 4 mol% Eu^(3+) doped Na_5Lu_9F_(32) single crystals are calculated as(x=0.626, y=0.3736), which are close to the NTSC standard values for red(x=0.67, y=0.33). The experimental results reveal that the single crystal can be used as potential red phosphors under near ultraviolet(NUV) light excitation.

2.0-μm emission and energy transfer of Ho^(3+)/Yb^(3+) co-doped LiYF_4 single crystal excited by 980 nm

Ho3＋/yb3＋ co-doped LiYF4 single crystals with various Yb3＋ concentrations and ,-~ 0.98 mol% Ho3＋ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient （40 ~C/cm-50 ~C/cm） for the solid-liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3＋ single-doped LiYF4 crystal, the Ho3＋/yb3＋ co-doped tiYf4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3＋ to Ho3＋ and the optimum fluorescence emission around 2.0 p-m of Ho3＋ ions are investigated. The maximum emission cross section of the above sample at 2.0 p.m is calculated to be 1.08 × 10-20 cm2 for the LiYF4 single crystal of 1-mol% Ho3＋ and 6-mo1% Yb3＋ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3＋ to Ho3＋ ion in the sample co-doped by Ho3＋ （1 mol%） and Yb3＋ （8 tool%） demonstrates that the Yb3＋ ions can efficiently sensitize the Ho3＋ ions.

Spectroscopic Properties of Nd^(3+)-Doped Tellurite Glasses

The Nd^3＋-doped pared. The absorption and tellurite glasses were preemission spectra of Nd^3 ＋- doped tellurite glasses at room temperature were measured. The Judd-Ofelt parameters （Ω2, Ω4, Ω6） of the glasses were calculated from measured absorption spectra. The calculation results of luminescence properties （A, β, τrad, σ） of Nd^3＋ ions in the tellurite were glasses were given. Spectroscopic properties, concentration quenching in these kinds of the glasses were investigated. The results indicate that the tellurite glasses with composition of 70% TeO2, 20% ZnO, （ 10 - x ） % La2O3, x % Nd2O3 （ mol% ） show high emission cross section and low phonon energy. The fluorescent intensity and the emission cross section have a maxi- mum value at x = 0.5, namely, the optimum Nd^3 ＋ ion concentration in the tellurite glass is 0.5% （1.93 × 10^20 ions·cm^-3）. The fluorescence properties of Nd^3＋ measured are basically in accord with the calculated results.

Effect of Al^3＋ on Photoluminescence Properties of Eu^3＋-Doped BaZr（BO3）2 Phosphors

We discuss the influence of Al^3＋ on the charge transfer state （CTS） and the photoluminescence properties of BaZr（BO3）2：Eu. The results reveal that there is a red shift which is about 20nm for the charge transfer state when doping with Al^3＋ and indicate the formation of ‘free＇ electrons due to the change of microstructures. In addition, the influence or Al^3＋ doping on the PPR is analysed and a new explanation is raised based on the photo luminescent mechanism. It is the CTS intensity rather than the CTS energy that influences the peak-peak ratio.

Upconversion Luminescence Dynamics in Er^3＋/Yb^3＋ Codoped Nanocrystalline Yttria

The upconversion luminescence and dynamics in Er^3＋ /Yb^3＋ codoped nanocrystalline yttria （7-65 nm） are studied under 980-nm pulsed laser excitation, It is found that the red emission of ^4F9/2-^4I15/2 and the green emission of ^2H11/2/^4S3/2 in nanoparticles with lower concentration of Yb^3＋ result from a two-photon excitation, In nanocrystals with higher Yb^3＋ concentration, the red emissions from a two-photon excitation, while the green emissions from a three-photon excitation, The luminescence dynamics indicates that as the particle size decreases, both the rise and the decay time constants become shorter, As the size decreases to several nanometres, the rise process nearly disappears, suggesting that the upconversion luminescence originates mainly from self-excitation of Er^3＋, instead of the energy transfer of Yb^3＋→ Er^3＋.

Upconversion Luminescence from Ho3＋ and Yb3＋ Codoped α-NaYF4 Single Crystals

The Ho3＋/yb3＋ co-doped a-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient （70-90℃ /cm） of solid-liquid interface was adopted. Upconversion emissions at green -544 nm, red -657 and -751 nm were obtained under 980 nm laser diode excitation. The intensity at -544 nm was much stronger than those of -657 and -751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb3＋ concentration was about 8.08moi% when Ho3＋ concentration was hold at about 1.0mol%. The results showed that Ho3＋/yb3＋ doped α-NaYF4 single crystal was a possible candidate upconversion material for the green solid-state laser.

Growth and Optical Spectra of Tb^(3+)/Eu^(3+) Co-doped Cubic NaYF_4 Single Crystal for White Light Emitting Diode

High quality Tb^3＋/Eu^3＋ co-doped cubic NaYF 4 single crystal in the size of Φ1.0 cm×6.6 cm was grown by a modified Bridgman method using KF as assistant flux for NaF-YF 3 system under the condition of completely closed Pt crucible.A white light emission from the combination of the violet-blue,blue,green,orange,and red lights with chromaticity coordinates of x = 0.3107,y = 0.3274,correlated color temperature of T c = 6637 K,color rendering index of R a = 83,and color quality scale of Q a = 82 could be obtained from 1.51 mol%Tb^3＋ and 1.42 mol%Eu^3＋ co-doped cubic NaYF 4 single crystal when being excited by a 369 nm light.This indicates that Tb^3＋/Eu^3＋）co-doped cubic NaYF 4 single crystal has a potential application in white light emitting diode excited by ultraviolet light.

Enhanced emission at 2.85 μm of Ho^(3+)/Pr^(3+) co-doped α-Na YF_4 single crystal

The Ho^(3+)/Pr^(3+) co-doped Na YF4 single crystals with various Pr^(3+) concentrations and constant Ho^(3+) molar percentage of ~1% were grown by an improved Bridgman method.Compared with the Ho^(3+) single-doped Na YF4 crystal,an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation.The Judd-Ofelt strength parameters(?2,?4 and ?6) are calculated,the radiative transition probabilities(A),the fluorescence branching ratios(β) and the radiative lifetime(τrad) are obtained in the meantime.The energy transfer from Pr^(3+) to Ho^(3+) and the optimum fluorescence emission of Ho^(3+) ions around 2.85 μm are investigated.Moreover,the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10^(-20) cm2 for the Na YF4 single crystal with Ho^(3+) molar percentage of 1% and Pr^(3+) molar percentage of 0.5% according to the measured absorption spectrum.All results suggest that the Ho^(3+)/Pr^(3+) co-doped Na YF4 single crystal may have potential applications in mid-infrared lasers.

Growth and optical properties of Dy^(3+)/Eu^(3+) co-doped NaYF_4 single crystals with cubic lattice for white LED application

Dy3+/Eu3+ co-doped cubic lattice Na YF4 single crystal with high quality in the size of ~Φ1.0 cm×10.0 cm was grown by an improved Bridgman method using potassium fluoride(KF) as assistant flux. X-ray diffraction(XRD), absorption spectra, excitation spectra and emission spectra are measured to investigate the phase and luminescent properties of the crystal. The effects of excitation wavelength and concentrations of Dy3+ and Eu3+ ions on the luminescent characteristics are analyzed. The Na YF4 single crystal with the doping molar concentrations of 1.205% Dy3+ and 0.366% Eu3+ exhibits an excellent white light emission with chromaticity coordinates of x=0.321, y=0.332. It indicates that the Dy3+/Eu3+ co-doped cubic lattice Na YF4 single crystal can be a potential luminescent material for the ultraviolet(UV) light excited white light emitting diode(w-LED).

Luminescent properties of Tm^(3+)/ Ho^(3+) co-doped LiYF_4 crystals

Ho3+ with various concentrations and Tm3+ with molar concentration of 1.28% are co-doped in Li YF4(YLF) single crystals. The luminescent properties of the crystals are investigated through emission spectra, emission cross section and decay curves under the excitation of 808 nm. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission of Ho3+ around 2.05 μm are investigated. The emission intensity at 2.05 μm keeps increasing with the molar concentration of Ho3+ improved from 0.50% to 1.51% when the molar concentration of Tm3+ is kept at 1.28%. Moreover, for the co-doped crystals in which the molar concentrations of Tm3+ and Ho3+ are 1.28% and 1.51%, respectively, the maximum emission cross section reaches 0.760×10–20 cm2 and the maximum fluorescence lifetime is 21.98 ms. All the parameters suggest that these materials have more advantages in the future 2.0 μm laser applications.

Tm^(3+) and Nd^(3+) singly doped LiYF_4 single crystals with 3-5 μm mid-infrared luminescence

Mid-infrared（MIR） emissions of 2.4 and 3.5 μm from Tm3＋：LiYF4 single crystals attributed to3H4 →3H5 and3H5 →3F4 transitions as well as MIR emissions of 4.2,4.3,and 4.5 μm from Nd3＋：LiYF4 lasers attributed to4I15/2 →4I13/2,4I13/2 →4I11/2,and4I11/2 →4I9/2 transitions,respectively,are observed.LiYF4 single crystals possess high transmittance of over 85% in the 2.5-6 μm range.The large emission crosssections of Tm-doped crystals at 2.4 μm（1.9×10-20cm2） and Nd-doped crystals at 4.2 μm（0.84×10-20 cm2） as well as the high rare-earth doping concentrations,excellent optical transmission,and chemicalphysical properties of the resultant samples indicate that Nd3＋and Tm3＋singly doped crystals may be promising materials for application in MIR lasers.

Enhanced cooperative near-infrared quantum cutting in Pr～(3+)-Yb～(3+)co-doped phosphate glass

Pr3+and Yb3+co-doped phosphate glasses are prepared to study their optical properties.Excitation and emission spectra and decay curves are used to characterize their luminescence.We demonstrate that upon excitation of Pr3+ion with one high energy photon at 470 nm,two near-infrared(NIR)photons are emitted at 950-1100 nm(Yb3+:2F 5/2 →2F 7/2)through an efficient cooperative energy transfer(CET)from Pr3+to Yb3+.The maximum energy transfer efficiency(ETE)and the corresponding quantum efficiency approach up to 90.17%and 190.17%,respectively.The glass materials might find potential application for improving the efficiency of silicon-based solar cells.

Ce^(3+) -Gd^(3+) co-doped high efficiency oxide glasses and transfer efficiency from Gd^(3+) to Ce^(3+)

The rare earth Ce3+ ion doped SiO2-B2O3-BaO-Gd2O3 system is synthesized by high-temperature melting method. The density, transmission, excitation spectra and scintillating properties of the glasses are investigated. The results indicate that all the samples have good physical and scintillating properties. The emission peak wavelength of all samples is 390 nm under X-ray radiation. Gd3+ ions have a negative impact on scintillating properties when its concentration reaches a certain level. Gd3+ ions sensitize the luminescence of Ce3+ ions, and the ideal concentration is 15 mol% for Gd3+ ions. Also the decay characteristics of Ce3+ and Gd3+ ions are investigated. These samples have potential practical applications in high energy physics.

Spectral properties and energy transfer in Er^(3+)/Yb^(3+) codoped LiYF_4 crystal

Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3+ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3+/Yb3+ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3+ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3+ singly doped crystal to 23.01 ms for Er3+/Yb3+ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3+/Yb3+ co-doped crystals are analyzed, and the possible energy transfer processes from Yb3+ to Er3+ are proposed.

Broadband near-infrared luminescence and energy trans-fer in Bi singly-doped and Bi/Yb co-doped titanate glasses

Super-broadband near-infrared(NIR)emission from 1100 nm to 1600 nm is observed in Bi-doped titanate glasses at the excitation of 808 nm laser diode(LD).The effects of Bi content on the optical spectra are investigated.It is also found that the Bi-related emission intensity can be enhanced by Yb3+co-doping at the excitation of 980 nm LD.It should be ascribed to the energy transfer from Yb3+to active Bi ions.The energy transfer processes are studied based on the Inokuti-Hirayama(I-H)model,and the energy transfer of electric dipole-dipole interaction is confirmed to be dominant in Bi/Yb co-doped glasses.

Ce^(3+)ion-doped α-NaYF_4 single crystal for UV laser

A Ce^（3＋）tion-doped α-Na YF_4 single crystal of high quality is grown successfully by an improved flux Bridgman method under the conditions of taking the chemical raw composition of Na F：KF：YF_3：CeF_3 in the molar ratio of30∶18∶48∶4, where the KF is shown to be an effective assistant flux. The x ray diffraction, absorption spectra,excitation spectra, and emission spectra of the Ce^（3＋）t-doped α-Na YF_4 single crystal are measured to investigate the phase and optical properties of the single crystals. The absorption spectrum of the Ce^（3＋）t：α-Na YF_4 shows a strong band that peaks at the wavelength of 300 nm. The emission spectrum of the Ce^（3＋）t：α-Na YF_4 emits an intense ultraviolet（UV） band at the wavelength of 332 nm under the excitation of 300 nm light. Two separated luminous bands of 330 and 350 nm, which correspond to the transitions 5d → 2F25∕2and 5d → F7∕2, can be obtained by Gauss fitting. The strong emission intensity at the UV band and the excellent optical transmission in the range of UV wavelengths indicate that Ce^（3＋）t：α-Na YF_4 single crystals can be considered as a promising material for UV lasers.