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 Li YF4 single crystals with various Yb3+concentrations and ～ 0.98 mol% Ho3+concentration are grown by the Bridgman method under the conditions of taking Li F 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 Li YF4 crystal,the Ho3+/Yb3+co-doped Li YF4 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 μm of Ho3+ions are investigated.The maximum emission cross section of the above sample at 2.0 μm is calculated to be 1.08×10-20cm2 for the Li YF4 single crystal of1-mol% Ho3+and 6-mol% Yb3+according to the measured absorption spectrum.The high energy transfer efficiency of88.9% from Yb3+to Ho3+ion in the sample co-doped by Ho3+(1 mol%) and Yb3+(8 mol%) demonstrates that the Yb3+ions can efficiently sensitize the Ho3+ions.     

Spectroscopic characterization of Yb:Sc₂O₃ transparent ceramics

Yb:Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm 1 . There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth (11 nm) and an emission cross-section of 1.8×10 20 cm 2 . The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb:Sc 2 O 3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb:Sc2O3 transparent ceramics are a promising material for short pulse lasers.     

Spectroscopic characterization of Yb:Sc2O3 transparent ceramics

Yb：Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm-1. There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth （11 nm） and an emission cross-section of 1.8×10^-20 cm^2. The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb：Sc2O3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb：Sc2O3 transparent ceramics are a promising material for short pulse lasers.     

Spectral properties of Ce3+ doped yttrium lanthanum oxide transparent ceramics

Ce3+-doped yttrium lanthanum oxide (Y0.9La0.1)2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce:(Y0.9La0.1)2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3+ ions at 230 nm and 400 nm, separately. It is found that Ce3+ ions can efficiently produce emission at 384 nm from (Y0.9La0.1)2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 (Re=Y, Lu, La) host materials.     

Fabrication and properties of tape-casting transparent Ho:Y_3Al_5O_(12) ceramic

High-quality holmium-doped Y3Al5O12(YAG) ceramic is fabricated in sequence by tape-casting and vacuum sintering. The average grain size of the Ho:YAG ceramic is around 20 μm with a fully dense microstructure. The inline transmittance of the sample is ～82% in visible and IR region. The fluorescence lifetime at 2088 nm is8.17 ms. The excellent properties of the Ho:YAG ceramic demonstrate the tape-casting is a novel candidate process for the fabrication of Ho:YAG-based thin-chip or composite ceramics.     

Energy transfer mechanism in Er3＋ doped fluoride glass sensitized by Tm3＋ or no3＋ for 2.7-μm emission

Enhanced 2.7 μm emission is obtained in Er3＋/Tma＋ and Era＋/Ho3＋ codoped ZBYA glasses. Absorp- tion and emission spectra are tested to characterize the 2.7 μm emission properties of Era＋/Tm3＋ and Era＋/Ho3＋ doped ZBYA glasses and a reasonable energy transfer mechanism of 2.7 μm emission between Er3＋ and Tm3＋Ho3＋） ion is proposed. Codoping of Tm3＋ or Ho3＋ significantly reduces the lifetime of the Era＋： 4I13/2 level due to the energy transfer of Er3＋：4I13/2 →Tm3＋：3F4 or Er3＋：4I13/2 →Ho3＋： 5I7. Thus, the 2.7μm emission is strengthened and the 1,5μm emission is decreased accordingly especially in the Era＋/Tma＋ sample. The upconversion effects between the Er3＋/Tm3＋ and Er3＋/Ho3＋ doped ZBYA glasses are different attribute to the different energy transfer efficiencies. Both of the two codoped samples possess nearly equal large emission cross section （16.6 × 10 -21 cm-2） around 2.7 μm. The results indicate that this Er3＋/Tm3＋ or Er3＋/Ho3＋ doped ZBYA glass has potential applications in 2.7 μm laser.     

Judd-Oflet analysis of spectrum and laser performance of Ho：YAP crystal end-pumped by 1.91μm Tm：YLF laser

The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.     

Nd^3＋, Yb^3＋ and Ho^3＋ Codoped Oxyfluoride Glass Ceramics with High Efficient Green Upconversion Luminescence

New oxyfluoride g/asses and glass ceramic codoped with Nd3 , Yb3 and Ho3 were prepared. The x-raydiffraction analysis revealed that the heat treatments of the oxyfluoride g/asses could cause the precipitationof (Nd^3 , Yb^3 , Ho^3 )-doped fluorite-type crystals. Very strong green up-conversion luminescence due to theHo3 : (^5F4, ^5S2)→ ^5I8 transition under 800-nm excitation was observed in these transparent glass ceramics.The intensity of the green up-conversion luminescence in a 1-mo1% YbF3-containing glass ceramic was found tobe about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho^3 up-conversion luminescence in the oxyfluoride g/ass ceramics is discussed.     

Spectroscopic properties in Er³⁺/Yb³⁺ Co-doped fluorophosphate glass

Using the technique of high-temperature melting, a new Er 3+ /Yb 3+ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er 3+ and Yb 3+ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd–Ofelt theory, the oscillator strength was computed. The lifetime of 4 I 13/2 level (τ m ) of Er 3+ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 μm. The large stimulated emission cross section of the Er 3+ was calculated by the McCumber theory. The spectroscopic properties of Er 3+ ion were compared with those in different glasses. The full width at half maximum and σ e are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.     

Acousto-optic Q-switched laser performances of Er3+:Yb3+:LuAl3（BO3）4 crystal at 1.5-1.6 μm

Diode-pumped acousto-optic Q-switched pulse laser at 1.5-1.6 μm is obtained in an Er3+:Yb3+:LuAl3 (BO3)4 crystal. Single-pulse laser operation with slope efficiency of 14% and threshold of approximately 100 mW is realized at an average absorbed pump power of 314 mW and repetition frequency of 20 kHz. Output pulse energy is 67 μJ. The effects of pulse repetition frequency, absorbed pump power, and duty cycle on the wavelength and pulse profile of the Q-switched Er3+:Yb3+:LuAl3(BO3)4 laser are also investigated.     

Investigation of up-conversion luminescence properties of RE/Yb co-doped Y2O3 transparent ceramic (RE=Er, Ho, Pr, and Tm)

RE/Yb co-doped Y₂O₃ transparent ceramics (RE=Er, Ho, Pr, Tm) were fabricated and characterized from the point of up-conversion luminescence. All the samples exhibit high transparence not only in near-infrared band (NIR) band but also in visible region, which ensures the output of the up-conversion luminescence. Under 980 nm excitation, green and red emissions were observed in Er, Yb:Y₂O₃ transparent ceramic, while green emission was detected in Ho, Yb and Pr, Yb co-doped Y₂O₃ transparent ceramics. In Tm, Yb co-doped Y₂O₃ ceramic, very intense blue up-conversion luminescence was detected. The dependence of up-conversion emission intensity on the pumping power was measured for each RE/Yb co-doped Y₂O₃ transparent ceramic, and the up-conversion mechanism was discussed in detail. Meanwhile, the energy transfer efficiency was calculated.     

Effect of Nd concentration on structural and optical properties of Nd:Y2O3 transparent ceramic

Y₂O₃ transparent ceramics with different Nd concentration (0.1-7.0at%) were fabricated using ZrO₂ as additive. All the samples exhibit high transparency over a broad spectral region. The elements (Y, O and Nd) are uniformly distributed in the ceramic body, and the average grain size increases with Nd content. Based on the absorption spectrum, the Judd-Ofelt intensity parameters are calculated (Ω₂=4.364×10⁻²⁰ cm², Ω₄=3.609×10⁻²⁰ cm² and Ω₆=2.919×10⁻²⁰ cm²). The absorption coefficients increase linearly with Nd³⁺ doping concentration. The absorption cross-section at 804 nm and stimulated emission cross-section at 1078 nm are calculated to be 1.54×10⁻²⁰ and 7.24×10⁻²⁰ cm², respectively. All the emission bands exhibit the highest emission intensities with 1.0at% Nd³⁺ ion content, while the lifetime decreases dramatically from 321.5 μs (0.1at% Nd) to 17.9 μs (7.0at% Nd). According to the emission spectra and measured lifetime, the optimum doping concentration of Nd³⁺ ion in Y₂O₃ transparent ceramic might be around 1.0at%.     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Photoluminescence properties and effects of dopant concentration in Bi2ZnB2O7:Tb phosphor

A novel green phosphor, Tb³⁺ doped Bi₂ZnB₂O₇ was synthesized by conventional solid state reaction method. The phase of synthesized materials was determined using the XRD, DTA/TG and FTIR. The photoluminescence characteristics were investigated using spectrofluorometer at room temperature. Bi₂ZnB₂O₇:Tb³⁺ phosphors excited by 270 nm and 485 nm wavelengths. The emission spectra were composed of three bands, in which the dominated emission of green luminescence Bi₂ZnB₂O₇:Tb³⁺ attributed to the transition ⁵D₄ → ⁷F₅ is centered at 546 nm. The dependence of the emission intensity on the Tb³⁺ concentration for the Bi_2−xTb_xZnB₂O₇ (0.01 ≤ x ≤ 0.15) was studied and observed that the optimum concentration of Tb³⁺ in phosphor was 13 mol% for the highest emission intensity at 546 nm.     

Spectral properties of Nd-doped Sr3Ga2Ge4O14 crystal

Neodymium doped strontium gallogermanate crystals were grown successfully by the Bridgman technique. The linear thermal expansion coefficients for the c- and a-axes were measured as 5.8 × 10⁻⁶ °C⁻¹ and 6.5 × 10⁻⁶ °C⁻¹. Absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the ⁴F_3/2 level was determined to be approximately 73.8% for this material. Compared with other Nd³⁺-doped laser crystals, Nd³⁺-doped Sr₃Ga₂Ge₄O₁₄ crystal displays special laser properties due to its disorder structure.     

Phosphorescent and thermoluminescent properties of SrAl2O4:Eu,Dy phosphors prepared by solid state reaction method

Long persistent SrAl₂O₄:Eu²⁺ phosphors co-doped with Dy³⁺ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl₂O₄ were observed in all the samples. The broad band emission spectra at 497 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ were observed and the emission is attributed to the 4f⁶5d¹ to 4f⁷ transition of Eu²⁺ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy³⁺ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence.     

Frequency measurements on far-infrared emissions from12C16O2-pumped methyl chloride and from12C18O2-pumped difluoromethane

The frequencies of 42 far-infrared laser lines have been measured by mixing with high-order harmonics of microwave frequencies in a Josephson junction. A total of 5 emissions between 334 and 1887 m have been measured from¹²C¹⁶O₂-pumped methyl chloride (CH₃Cl) and 37 emissions between 116 and 1092 m in¹²C¹⁸O₂-pumped difluoromethane (CH₂F₂). Additional data is given on the laser emission characteristics.Division of Electrical Science, National Physical Laboratory     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Multiplication of electronic excitations in nanophosphors Lu2O3:Eu and Lu2O3:Tb

Luminescence properties of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanocrystalline powders with the particle size varying from 46 to 6 nm were studied under excitation by synchrotron radiation in the photon energy range (up to ∼22.5 eV) covering the region where the processes of multiplication of electronic excitation occur. It was found that the excitation spectra of Tb³⁺ emission from all Lu₂O₃:Tb³⁺ nanopowders have similar behavior, whereas the shape of the excitation spectra of Eu³⁺ emission from Lu₂O₃:Eu³⁺ nanopowders strongly depends on the particle size. The difference in the behavior of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanophosphor systems was explained by different mechanisms of the energy transfer from the host to Eu³⁺ or Tb³⁺ ions (either the hole or electron recombination mechanism, respectively), which are differently influenced by losses of electronic excitations near the particle surface.