Spectroscopic and laser properties of Er3+-doped monoclinic BaY2F8 single crystals

The luminescence and absorption properties of Ba(Y_1−x Er _x )₂F₈ (x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er³⁺-ion decay kinetics of luminescent transitions from three initial laser states, the⁴S_3/2,⁴F._9/2 and⁴I_11/2 manifolds, were measured. The crystal-field splitting schemes for allJ-manifolds which are involved in (J →J′)-luminescence transitions and stimulated emission parameters of Er³⁺ -ions in BaY₂F₈ were determined. A comparison of laser powers and efficiencies of BaY₂F₈ and Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and LiYF₄ single crystals doped with Er³⁺-ions shows the similar performance of these materials.

     

Upconverted 5d-4f luminescence from Er and Nd ions doped into fluoride hosts excited by ArF and KrF excimer lasers

We report on observation of upconverted VUV luminescence due to 5d-4f radiative transitions in Er³⁺ and Nd³⁺ ions doped into some fluoride crystals, under excitation by ArF and KrF excimer lasers, respectively. Only spin-forbidden 5d-4f luminescence of Er³⁺ (at 165 nm) was detected from the LiYF₄:Er³⁺ crystal whereas both spin-forbidden (at 169 nm) and spin-allowed (at 160.5 nm) components are observed from the BaY₂F₈:Er³⁺ crystal, the latter being much weaker than in the case of one-photon excitation. Nd³⁺ 5d-4f luminescence at 180 and 173 nm has been detected from the LiYF₄:Nd³⁺ and LaF₃:Nd³⁺ crystals, respectively. The shift of short-wavelength edge of 5d-4f emission spectra towards longer wavelengths is observed under temperature increase from 15 to 293 K. The observed effects in the spectra of Er³⁺ and Nd³⁺ doped crystals were interpreted as a result of reabsorption of 5d-4f luminescence escaping from the bulk of the crystals.     

Efficiency of the generation and self-addition of laser line frequencies upon the diode pumping of Er:BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Features of the generation of laser lines upon the diode pumping of Er:BaY₂F₈ crystals are studied. Blue, violet, and UV laser lines are most efficiently generated via the nonlinear frequency self-addition of 541 and 553 nm lines of Er³⁺ radiation with the corresponding IR line of Er³⁺ for Er:BaY₂F₈ crystals pumped by a laser diode with a wavelength of 972 nm.     

VUV luminescence of Er<Superscript>3+</Superscript> ions in LiYF<Subscript>4</Subscript> and BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Vacuum ultraviolet luminescence of Er³⁺ ions in LiYF4 and BaY₂F₈ crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er³⁺ ions are observed. It is shown that from the LiYF₄:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY₂F₈:Er crystal.     

Green up-conversion of Er3+ in KGd(WO4)2 crystals. Effects of sample orientation and erbium concentration

Pumping with infrared light resonant to the energy position of ⁴ I _11/2 and ⁴ I _9/2 multiplets respectively has excited green up-conversion of Er³⁺ in KGd(WO₄)₂ single crystal. At room temperature the maximum green-emission intensity is achieved by pumping with light polarized parallel to the C₂ symmetry axis of the crystal (//p) at 981 and 801.5 nm, while pumping with light parallel to the principal m axis (//m) has maximum up-conversion at 978.2, 806 and 800 nm. The emission is weakly polarized. The maximum of the emission peaks at 547.8 nm if the light is analyzed parallel to the C₂ axis or at 552.4 nm for light perpendicular to it. The largest emission intensity was achieved with an erbium concentration about 3×10²⁰ cm^-3. A schematic model of the up-conversion process is suggested. Received: 4 July 2000 / Published online: 22 November 2000     

1313nm脉冲泵浦下掺Er3+光纤中多波长可见光的产生

本文报道了以1313nmNd:YLF激光脉冲泵浦掺饵(Er³⁺)单模GeO₂/SiO₂光纤而产生多波长可见光的实验,在该光纤中观察到(463～510)nm间的多波长放大自发辐射过程,此过程对应于Er³⁺离子的²G_7/2等几个激发态到⁴I_13/2亚稳态的跃迁.其激发过程是分步的四光子吸收过程,同时,掺饵光纤的红外发射峰1530nm(⁴I_13/2-⁴I_15/2)与1313nm泵浦光之间的三波混频过程也对这一区间的连续多峰的光谱结构有贡献.实验中还观察到540nm附近的绿光辐射.     

The effect of Y co-doping on the persistent up-conversion luminescence of the ZrO2:Yb,Er nanomaterials

The effect of the defects due to the charge compensation obtained with the yttrium co-doping to the ZrO₂:Yb³⁺,Er³⁺ up-converting phosphors was studied. The materials were prepared with the combustion method. The materials purity was analyzed with the FT-IR spectroscopy. The crystal structure was studied with the X-ray powder diffraction and the crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence was excited at room temperature with an IR-laser at 970 nm. The up-conversion luminescence spectra showed red (650-685 nm) and green emission (520-560 nm) due to the ⁴F_9/2→⁴I_15/2 and (²H_11/2,⁴S_3/2)→⁴I_15/2 transitions of Er³⁺, respectively. Persistent up-conversion luminescence was observed both in the Yb³⁺,Er³⁺ and Y³⁺,Yb³⁺,Er³⁺ doped materials.     

Optical transitions of Pr3+ and Er3+ ions in LiYF4

The optical absorption, emission, and excitation spectra of Pr³⁺ and Er³⁺ ions in LiYF₄ have been measured and energy level schemes established which agree with previous work. The temperature dependence of the emission lifetimes were investigated and analyzed using the Huang-Rhys and Struck-Fonger treatments of multiphonon decay. The non-radiative processes in LiYF₄: Er³⁺ were shown to follow the same “gap law” behavior as Er³⁺ in LaF₃ and MnF₂. Theoretical fits to the Huang-Rhys model allowed the construction of a configuration coordinate diagram for the Er³⁺ system. The non-exponential temperature dependence of the ¹D₂ lifetime in Pr³⁺ can be understood as a non-radiative transition from higher levels.     

Upconversion emission in CaTiO3:Er3+ nanocrystals

CaTiO₃:Er³⁺ (5%) nanocrystals were obtained by sol–gel method under acidic conditions. The sizes of nanocrystals were 40 nm. Strong green anti-Stokes emission was observed after excitation of the ⁴I_9/2 and ⁴I_11/2 level. The emission is due to excited state absorption (ESA) and energy transfer upconversion (ETU).     

Doubly doped BaY2F8:Er,Nd VUV scintillator

Doubly doped BaY₂F₈:Er,Nd scintillation crystals were grown by modified micro-pulling-down method. The Er co-doping was chosen to enhance the energy transfer from the host lattice to the Nd³⁺ luminescence center via the 5d-levels of Er³⁺, which can be enabled by the overlap of Er³⁺ 5d-4f emission spectrum with the Nd³⁺ 4f-5d absorption. The energy transfer was clearly evidenced in the BaY₂F₈:Er,Nd. The processes are complicated by energy migration to killer centres and/or cross-relaxation processes. The luminescence and energy transfer mechanism are discussed.     

Site-selective spectroscopy of Er3+:Ti:LiNbO3 waveguides

Starting from previous investigations in LiNbO₃ bulk crystals, we studied the optical properties of Er³⁺ ions in Ti:LiNbO₃ channel waveguides and investigated the waveguide-specific lattice environment of the Er³⁺ ions (“sites”) caused by the doping method used and the presence of a large number of Ti⁴⁺ ions. For that purpose the method of combined excitation–emission spectroscopy was applied for the first time to waveguides at low temperatures. Comparing the spectroscopic results obtained for the green, red, and near-IR luminescence (λ≈550, ≈650 and ≈980 nm) under direct (450 nm), 2-step (980 nm), and 3-step (1.5 μm) laser excitation, we found several distinguishable Er³⁺ sites which in terms of energy levels and relative numbers are similar to those in bulk material, but exhibit significantly different up-conversion efficiencies and strongly inhomogeneously broadened transitions. Moreover, we were able to distinguish isolated and cluster Er³⁺ sites by their characteristic excitation and emission transition energies and studied the respective excitation/relaxation channels. The cluster sites are most efficient in the up-conversion process, especially under 3-step excitation. Using accepted microscopic models for Er³⁺ and Ti⁴⁺ incorporation into the LiNbO₃ crystal lattice, the site distribution and up-conversion mechanisms are elucidated and their consequences for laser applications in different spectral regions are discussed. Received: 16 November 2000 / Published online: 21 March 2001     

Photoluminescence characteristics of energy transfer between Er and Bi in Gd2O3: Er, Bi

The phosphors, Bi³⁺- activated Gd₂O₃:Er³⁺, were prepared by sol-gel combustion method, and their photoluminescent properties were investigated under ultraviolet light excitation. The emission spectrum exhibited sharp peaks at about 520, 535, 545, 550 and 559 nm due to (²H_11/2, ⁴S_3/2)→⁴I_15/2 transitions of Er³⁺ ions. The luminescent intensity was remarkably improved by the incorporation of Bi³⁺ ions under 340 nm light excitation, which suggested very efficient energy transfer from Bi³⁺ ions to Er³⁺ions. The introducing of Bi³⁺ ions broadened the excitation band of the phosphor, of which a new strong peak occurred ranging from 320 to 360 nm due to the 6s²→6s6p transition of Bi³⁺ ions. There is significant energy overlap between the emission band of Bi³⁺ ions and the excitation band of Er³⁺ ions. Under 340 nm light excitation, Bi³⁺ absorbed most of the energy and transferred it to Er³⁺. The energy transfer probability from Bi³⁺ to Er³⁺ is strongly dependent on the Bi³⁺ ion concentration. Also, the sensitization effectiveness was studied and discussed in this paper.     

The UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

共沉淀法制备Y2SiO5∶Er3+ ,Yb3+ ,Tm3+及其上转换发光性能研究

采用化学共沉淀法制备了系列Y_1.98-2xYb_2x Er_0.02SiO₅(0.00≤x≤0.15)以及Y_1.736Yb_0.24Er_0.02Tm_0.004SiO₅上转换发光材料,比较了室温下Y_1.98-2xYb_2x Er_0.02 SiO₅ (x=0.00,0.08)样品在400—1600 nm范围内的吸收光谱,测量了所有样品在976 nm OPO激光器激发下的上转换发射光谱,以及Er³⁺离子⁴S_3/2(⁴F_9/2)→⁴I_15/2,Tm³⁺离子¹G₄→³H₆荧光衰减曲线和不同激发功率下的上转换蓝光发射强度,从而分析讨论了Er³⁺,Tm³⁺在Y₂SiO₅中的上转换发光机理.研究结果表明:在1250 ℃相对较低的温度下合成了X2型单斜晶系Y₂SiO₅ ∶Ln³⁺(Ln³⁺=Er³⁺,Yb³⁺,Tm³⁺),Yb³⁺的敏化显著增强了样品在976 nm附近的吸收能力,并大幅度加宽了该处的吸收带.分析上转换发射光谱发现:上转换绿光和红光强度都随着Yb³⁺浓度的增加先增强后减弱,但红光的猝灭浓度较高,归因于Er³⁺→Yb³⁺反向能量传递ETU4和Yb³⁺→Er³⁺正向能量传递ETU3过程的发生;上转换蓝光发射是三光子吸收过程,是通过Yb³⁺,Tm³⁺之间三次声子辅助的能量转移方式实现的. 关键词： 上转换 共沉淀 2SiO₅∶Er³⁺')" href="#">Y₂SiO₅∶Er³⁺ 3+')" href="#">Yb³⁺ 3+')" href="#">Tm³⁺     

Infrared-to-visible frequency upconversion in SrAl2O4 powders containing Er3+ and Yb3+

The phenomenon of frequency upconversion (UC) is observed in Er³⁺:Yb³⁺:SrAl₂O₄ powders prepared by combustion synthesis. Strong UC emission at the green (bands peaked at 521, 538, 547, and 562 nm) and weak UC emission at the red (bands peaked at 659 and 682 nm) corresponding to 4f–4f transitions of Er³⁺ were observed when the samples were irradiated with near-infrared laser excitation at ～980 nm. Saturation of UC emission is observed for concentrations of 1.5 wt.% of Er³⁺ and 1.5 wt.% of Yb³⁺. The green-to-red intensity ratio, on the other hand, increases linearly with Er³⁺ concentration (Er³⁺ concentration varying from 0.5 to 1.5 wt.%) while keeping Yb³⁺ concentration fixed (at 1.5 wt.%). The green UC decay time was measured and Er³⁺–Er³⁺ interaction was suggested as a possible mechanism to explain the luminescence quenching effect observed.     

Towards new lasers in Ti:Er:LiNbO3 waveguides: a study of the excited Er3+ states

Detailed excited state absorption measurements under pumping at 980 nm and 1.5 μm together with conventional absorption and emission spectroscopy is employed to investigate optical transitions of Er³⁺ in Ti:LiNbO₃ channel-waveguides. The experimental data were evaluated using the Judd–Ofelt method giving parameters close to those in the bulk. The good agreement between theoretical prediction and measurements allows us to calculate cross section, lifetimes, and branching ratios. Based on these results we developed and tested a model which is able to predict the conditions for which laser operation at 550 nm and 2.7 μm will be possible under 980 nm pumping. Received: 9 December 1998 / Revised version: 8 January 1999 / Published online: 24 March 1999     

Optical spectroscopy and diode-pumped laser characteristics of codoped Tm-Ho : YLF and Tm-Ho : BaYF : a comparative analysis

Single crystals of monoclinic BaY₂F₈ and tetragonal LiYF₄ codoped with the same Tm³⁺ and Ho³⁺ concentrations were successfully grown by the Czochralski method. Here we present a comparative analysis of the two hosts including spectroscopic characterization and cw diode-pumped laser experiments in the 2-μm wavelength region at room temperature. The main differences between the two hosts are a lower slope efficiency associated with a much wider tuning range (2005–2094 nm) of BaY₂F₈ with respect to LiYF₄. Received: 29 July 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/2214-333, E-mail: toncelli@df.unipi.it     

Optical properties and upconversions in Er doped Li:TeO2 glass

A NIR excitation of Er³⁺ doped Lithium modified tellurite (Li:TeO₂) glass results in antistokes fluorescent emission near 380, 530, 551 and 654 nm (ultraviolet, green and red regions) in addition to NIR Stokes emission. The antistokes emissions are ascribed to transition from the excited ⁴G_11/2, ⁴S_3/2(²H_11/2) and ⁴F_9/2 levels in Er³⁺. The excitation involves three and two incident photons. On excitation with the green laser line at 532 nm also leads to similar emissions. The mechanisms involved in these processes are discussed on the basis of the known energy level diagram and the upconversion efficiency has been calculated. Lifetime of the ⁴S_3/2 level has been measured. The temperature dependence of the upconversion process has also been investigated.     

Visible luminescence of nanocrystalline AlN:Er thin film by co-deposition of AlN,Er, and SiO2

We report a visible luminescence of Er³⁺ ions in an amorphous-nanocrystalline AlN:Er thin film prepared by co-deposition using AlN, Er, and SiO₂ targets. A PL emission spectrum of Er³⁺ in the AlN:Er film annealed at 750 °C showed a strong bluish green emission of Er³⁺ in the amorphous-nanocrystalline AlN:Er thin film, which is attributed to the intra-4fEr³⁺ transitions of ²H_11/2 → ⁴I_15/2 and ⁴F_7/2 → ⁴I_15/2. It was found that crystallite diameters were between 3 and 5 nm by high-resolution transmission electron microscopy. The occurrence of the strong Er³⁺ emission in the annealed AlN:Er thin film with a mixture of amorphous and nanocrystalline phases may be contributed to an increase in the number of excitation Er³⁺ centers and a presence of oxygen related to Er³⁺ excitation and recombination process in the AlN:Er thin film.     

Spectroscopic and laser properties of Er3+-doped monoclinic BaY2F8 single crystals

The luminescence and absorption properties of Ba(Y_1–x Er _x )₂F₈ (x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er³⁺-ion decay kinetics of luminescent transitions from three initial laser states, the⁴S_3/2,⁴F._9/2 and⁴I_11/2 manifolds, were measured. The crystal-field splitting schemes for allJ-manifolds which are involved in (J J)-luminescence transitions and stimulated emission parameters of Er³⁺ -ions in BaY₂F₈ were determined. A comparison of laser powers and efficiencies of BaY₂F₈ and Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and LiYF₄ single crystals doped with Er³⁺-ions shows the similar performance of these materials.