The influence of Zn2+ ion on the 1.5 μm laser properties of LiNbO3 crystal heavily doped with Er3+ ion

The spectral characteristics of 1.54 μm emission in a series of Zn/Er:LiNbO₃ crystals with heavy Er content and variable Zn content were reported. The inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of Er³⁺ ion in the crystal. The absorption and emission spectra of Zn/Er:LiNbO₃ crystals were measured. Based on Judd–Ofelt theory, the spectral parameters such as intensity parameters Ω_t (t=2, 4 and 6), transition strengths, radiative transition probabilities, radiative lifetime and fluorescence branching ratio have been obtained in Zn/Er:LiNbO₃ system. The emission cross section corresponding to ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ion was obtained according to Füchtbauer–Ladenburg theory. The gain cross section of Er:LiNbO₃ crystal codoped with 6 mol% Zn²⁺ ions were also discussed in this work.     

Photoluminescence of Er-doped Si-SiO2 and Al–Si-SiO2 sputtered thin films

Er-doped Si-SiO₂ and Al–Si-SiO₂ films have been deposited by rf-sputtering being annealed afterwards. Annealing behavior of the Er³⁺: ⁴I_13/2→⁴I_15/2 emission of Er-doped Si-SiO₂ yields a maximum intensity for annealing at 700–800 °C. ⁴I_13/2→⁴I_15/2 peak emission for Er-doped Al–Si-SiO₂ at 1525 nm is shifted from that for Er-doped Si-SiO₂ at 1530 nm and the bandwidth increases from 29 to 42 nm. ⁴I_13/2→⁴I_15/2 emission decays present a fast decaying component related to Er ions coupled to Si nanoparticles, defects, or other ions, and a slow decaying component related to isolated Er ions. Excitation wavelength dependence and excitation power dependence for the ⁴I_13/2→⁴I_15/2 emission correspond with energy transfer from Si nanoparticles. Populating of the ⁴I_11/2 level in Er-doped Si-SiO₂ involves branching and energy transfer upconversion involving two or more Er ions. Addition of Al reduces the populating of this level to an energy transfer upconversion involving two ions.     

Microwave sol–gel derived NaCaGd(MoO4)3:Er3+/Yb3+ phosphors and their upconversion photoluminescence properties

Ternary molybdate NaCaGd_1−x(MoO₄)₃:Er³⁺/Yb³⁺ phosphors with the proper doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0, 0.05, 0.1, 0.2 and Yb³⁺ = 0, 0.2, 0.45) were successfully synthesized by microwave sol–gel method for the first time. Well-crystallized particles formed after heat-treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 3–5 μm. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, which correspond to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions, and a very weak 655-nm emission band in the red region, which corresponds to the ⁴F_9/2 → ⁴I_15/2 transition. The optimal Yb³⁺:Er³⁺ ratio was obtained to be 9:1, as indicated by the composition-dependent quenching effect of Er³⁺ ions. The pump power dependence of upconversion emission intensity and Commission Internationale de L’Eclairage chromaticity coordinates of the phosphors were evaluated in detail.     

Intense 974 nm emission from ErxYb2−xSi2O7 films through efficient energy transfer up-conversion from Er3+ to Yb3+ for Si solar cell

The optical properties of the Er_xYb_2?xSi₂O₇ thin films were investigated by photoluminescence measurements and the intense 974 nm light emission was observed. The 974 nm emission was mainly from the transition ²F_5/2 to ²F_7/2 level of Yb³⁺ upon exploring energy-transfer via up-conversion at Er^{3+ 4}I_13/2 level. Under 972 nm excitation, the lifetime at Er^{3+ 4}I_13/2 level reaches up to 4 ms for film containing 2 at% Er³⁺, while decreases to about 20 μs as the film is pumped by 488 nm. This confirmed that the energy transfer up-conversion process was the dominant transition at Er^{3+ 4}I_13/2 level. This may be of interest to improve the solar cells′ efficiency by placing this film at the rear of cell, converting the near-infrared photons between 1480 nm and 1580 nm to just above the Si bandgap.     

Photoluminescence properties of Er-doped β-FeSi2 grown by ion implantation

Photoluminescence (PL) properties of Er-doped β-FeSi₂ (β-FeSi₂:Er) and Er-doped Si (Si:Er) grown by ion implantation were investigated. In PL measurements at 4.2 K, the β-FeSi₂:Er showed the 1.54 μm PL due to the intra-4f shell transition of ⁴I_13/2→⁴I_15/2 in Er³⁺ ions without a defect-related PL observed in Si:Er. In the dependence of the PL intensity on excitation photon flux density, the obtained optical excitation cross-section σ in β-FeSi₂:Er (σ=7×10⁻¹⁷ cm²) is smaller than that in Si:Er (σ=1×10^-15 cm²). In the time-resolved PL and the temperature dependence of the PL intensity, the 1.54 μm PL in β-FeSi₂:Er showed a longer lifetime and larger activation energies for non-radiative recombination (NR) processes than Si:Er. These results revealed that NR centers induced by ion implantation damage were suppressed in β-FeSi₂:Er, but the energy back transfer from Er³⁺ to β-FeSi₂ was larger than Si:Er.     

Dopant occupancy and optical properties of Er3+ in Er/Zn-codoped lithium niobate crystal

The effect of Zn²⁺ ion on the dopant occupancy and optical characteristic of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal is reported. The intense 1.54 μm and relatively weak green upconversion emissions are observed for Er (1 mol%)/Zn (6 mol%):LiNbO₃ crystal. The OH^? absorption and the time-resolved spectra show that the Zn²⁺ codoping decreases the threshold concentration of Er³⁺ ion in Er/Zn-codoped LiNbO₃ crystal. The experimental results here imply that the potential application of Er³⁺-doped LiNbO₃ crystal can be designed and optimized on the basis of the theoretical investigations.     

Comparative study of the spectroscopic properties of Yb3+/Er3+ codoped tellurite glasses modified with R2O (R=Li,Na and K)

Spectroscopic characterization of Yb³⁺/Er³⁺ codoped TeO₂–R₂O–ZnO–Ln₂O₃ glasses as a function of network modifiers (R=Li, Na and K) has been investigated. The Judd–Ofelt parameters (Ω_t), quantum efficiency in near infrared (1.55 μm) and visible up-conversion (546 and 660 nm) and quality factor spectroscopy (χ) were calculated. Three up-conversion emission bands centered at 525, 546 and 660 nm were observed as maxima for glasses containing potassium. The measured lifetime of ⁴I_13/2, ⁴F_9/2 and ⁴S_3/2 from Er³⁺ and ⁴F_5/2 from Yb³⁺ levels increased when potassium (K) replaced lithium (Li) and Na. The maximum emission cross-section (ECS) for ⁴I_13/2→⁴I_15/2 transition of Er³⁺ was calculated to be 1.02×10^?20 cm² for TeO₂–Li₂O–ZnO–Ln₂O₃ glasses. The energy transfer efficiency (ET) from Yb³⁺ to Er³⁺, (⁴F_5/2)+(⁴I_15/2)→(⁴F_7/2)+(⁴I_13/2), was calculated using the measured lifetimes of Yb³⁺ with and without the presence of acceptor (Er³⁺). The maximum calculated ET was 58% for 0.25 mol% of Er³⁺ and 3 mol% of Yb³⁺ for TeO₂–K₂O–ZnO–Ln₂O₃ glass composition.     

Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO₃ and Er/Yb:LiNbO₃ crystals were grown by the Czochralski technique. The laser characteristics of 1.54 μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ω_t (Ω₂=7.23×10^?20 cm², Ω₄=3.15×10^?20 cm² and Ω₆=1.43×10^?20 cm²) were obtained. The stimulated emission cross sections (σ_em) at 1.54 μm emission in Zn/Er/Yb:LiNbO₃ were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO₃ crystal was also investigated. Under 980 nm excitation, a lenghthening lifetime of 1.54 μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO₃ crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn²⁺ ion tridoping increases the probability of cross relaxation process between the two neighboring Er³⁺ ions.     

Spectroscopic analysis of Cr,Er:Gd3Ga5O12 crystals as candidates of potential xenon lamp pumped ~ 2.7 μm laser

A series of Cr,Er:Gd₃Ga₅O₁₂ crystals with high concentrations of Er^3 + were grown by Czochralski method. The absorption spectra, the up-conversion, near infrared (NIR) and mid-infrared (Mid-IR) luminescence spectra as well as the luminescence decay curves of Er: ⁴I_13/2 and ⁴I_11/2 levels were measured at room temperature. The spectroscopic properties of Cr,Er:Gd₃Ga₅O₁₂ crystals and Cr–Er energy transfer processes were investigated. The spectroscopy of the Er^3 +:⁴I_11/2 → ⁴I_13/2 transition was centralized to discuss, and the important optical parameters including luminescence lifetimes and the Cr–Er energy transfer efficiency are presented. Based on the comprehensive spectral analyses, 0.6 at.%Cr/50 at.%Er:GGG crystal is preferred as candidate of potential xenon lamp pumped ~ 2.7 μm laser in this work.     

Up-conversion luminescence and optical temperature-sensing properties of Er3+-doped perovskite Na0.5Bi0.5TiO3 nanocrystals

In this work we demonstrate the preparation of Er³⁺ doped perovskite ferroelectric Na_0.5Bi_0.5TiO₃ nanocrystals and their application in temperature sensing. The samples were synthesized via a facile hydrothermal method. Upconversion emission at 528 nm and 547 nm from two thermodynamically coupled excited states of Er³⁺ were recorded in the temperature from 80 K to 480 K under the excitation of a 980 nm diode laser. The emission intensity ratio (I₅₂₈/I₅₄₇) as a function of the temperature was investigated. A sensitivity of 0.0053 K⁻¹ is observed at 400 K, suggesting they are promising candidate for nanothermometers.     

Near-infrared broadband luminescence and energy transfer in Bi–Tm–Er co-doped lanthanum aluminosilicate glasses

The Bi–Tm–Er co-doped SiO₂–Al₂O₃–La₂O₃ (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission, were investigated by the optical absorption and photoluminescence spectra. A super broadband NIR emission extending from 0.95 to 1.6 μm with a full-width at half-maximum (FWHM) of 430 nm which covered the whole O, E, S, C and L bands, was observed in Bi–Tm–Er co-doped samples under 808 nm excitation, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm^{3+ 3}H₄→³F₄ transition (1450 nm) as well as Er^{3+ 4}I_13/2→⁴I_15/2 transition (1545 nm). In addition, a super broadband emission with amplitude relatively flat from 0.95 to 2.1 μm has been observed. The possible energy transfer between Bi-related centers, Tm³⁺ ions and Er³⁺ ions was proposed.     

Infrared to visible upconversion luminescence in Er3+/Yb3+ doped titanate glass prepared by containerless processing

Er³⁺ doped TiO₂–La₂O₃ glasses modified by ZrO₂ have been successfully fabricated by the containerless method with incorporated Yb³⁺ ions as sensitizers. Under the excitation of 980 and 808 nm diode lasers, visible emissions centered at 534, 554 and 674 nm are observed, which are assigned to the Er³⁺ transitions of ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2, respectively. The emission signals are so strong that they can be observed by naked eyes even at pumping power as low as 20 mW. Measurements of pump-power dependent intensity and time-resolved decay behavior of upconversion luminescence show that two-photon excited state absorption (ESA) and energy transfer (ET) between rare earth ions are the predominant mechanisms for upconversion emissions. Besides, the intensity of upconversion luminescence has been enhanced by increasing the concentration of ZrO₂ in these rare earth doped bulk titanate glasses.     

The growth and field evaporation of Er and deuterated Er films

The morphological structure of clean and deuterated Er films deposited on W substrates and their removal by field evaporation have been investigated as part of a program directed toward the development of deuterium ion sources for neutron generators. Annealed Er films up to ~ 20 monolayers in thickness deposited on W < 110 > substrates appear pseudomorphic. Thicker annealed films form a hexagonal close-packed < 0001 > orientated over-layer with the Pitsch–Schrader orientation relation. The pseudomorphic and hexagonal close-packed character of the films is retained up to the last atomic layer that forms the film-substrate interface. Deuterated Er films appear polycrystalline. At 77 K in Ar, annealed Er films field evaporate at 2.5 V/Å primarily as Er^2 + and deuterated Er films evaporate at ~ 2.4 V/Å primarily as ErD_x^2 +. Field evaporation of both clean and deuterated Er films shows signs of space charge induced field lowering when film thicknesses exceeding ~ 10 layers were field evaporated using 20 ns duration voltage pulses.     

Synthesis and luminescence properties of Gd6MoO12:Yb3+, Er3+ phosphor with enhanced photoluminescence by Li+ doping

Yb³⁺/Er³⁺ co-doped Gd₆MoO₁₂ and Yb³⁺/Er³⁺/Li⁺ tri-doped Gd₆MoO₁₂ phosphors were prepared by adjusting the annealing temperature via the high temperature solid-state method. Under the excitation of 980 nm semiconductor, the upconversion luminescence properties were investigated and discussed. In the experimental process, we get the optimum Yb³⁺ concentration and the concentration quench effect will happen while the concentration extends the given region. According to the Yb³⁺ concentration quenching effects, the critical distance between Yb³⁺ ions had been calculated. The measured UC luminescence exhibited a strong red emission near 660 nm and green emission at 530 nm and 550 nm, which are due to the transitions of Er³⁺(⁴F_9/2, ²H_11/2, ⁴S_3/2) → Er³⁺(⁴I_15/2). Then the effect of excitation power density in different regions on the upconversion mechanisms was investigated and the calculated results demonstrate that the green and red upconversion is a two-photon process. A possible mechanism was discussed. After Li⁺ ions mixing, the upconversion emission enhanced largely, and the optimum Li⁺ concentration was obtained while fixed the Yb³⁺ and Er³⁺ on the above optimum concentration. This enhancement owns to the decrease of the local symmetry around Er³⁺ after Li⁺ ions doping into the system. This result indicates that Li⁺ is a promising candidate for improving luminescence in some case.     

Positive influence of Tm3+ on effective Er3+: 3 μm emission in fluoride glass under 980 nm excitation

Er³⁺ and Tm³⁺ singly doped and codoped new fluoride glasses were prepared by traditional melt-quenching method. Efficient 3 μm emission was obtained under 980 nm laser excitation. It is worthy to notice that one of the two ions can be the sensitizer to the other one by depressing the Er³⁺: 1.5 μm emission through the energy transfer process from Er³⁺:⁴I_13/2 level to Tm³⁺:³F₄ level. On the basis of measured absorption spectra, the Judd-Ofelt intensity parameters and radiation emission probability were calculated to evaluate the spectroscopic properties. Additionally, the micro-parameters together with the phonon assistance of Er³⁺:⁴I_13/2 → Tm³⁺:³F₄ and Er³⁺:⁴I_11/2 → Tm³⁺:³H₅ processes were quantitatively analyzed by using Dexter model. The theoretical micro-parameters results meet well with the experiments which indicates that Er³⁺/Tm³⁺ codoped fluoride glass is a potential kind laser glass for 3 μm laser.     

Photoluminescence investigations of Li2SiO3:Ln (Ln=Er3+, Eu3+, Dy3+, Sm3+) phosphors

In this study, we report a comprehensive structural and photoluminescence (PL) study on lithium metasilicate (Li₂SiO₃) phosphor ceramics doped with four rare earth (RE) ions. X-ray diffraction (XRD) patterns show a dominant phase, characteristic of the orthorhombic structure Li₂SiO₃ compound and the presence of dopants has no effect on the basic crystal structure of the material. The first excited state Er³⁺ luminescence at 1.54 μm arises from a sharp atomic-like radiative transition between the ⁴I_13/2 state and the ⁴I_15/2 state (ground level) under a 532 nm line of an Ar ion laser excitation. Sm doped samples showed Sm³⁺ emission characteristics corresponding to the some ⁴G_5/2→⁶H_j (j=5/2,9/2,11/2) transitions indicating a strong crystal-field effect. PL spectra of Eu doped material exhibited peaks corresponding to the ⁵D₀→⁷F_j (j=0,1,2,3 and 4) transitions under 405 nm excitation. The dominant red color emission at 612 nm from the hypersensitive (⁵D₀→⁷F₂) transition of Eu³⁺ indicates the inversion antisymmetry crystal field around Eu³⁺ ion, which is favorable to improve the red color purity. Dy doped samples showed the Dy³⁺ emission characteristic due to the ⁴F_9/2→⁶H_13/2 transition. Their relative intensity ratios also suggested the presence of a symmetric environment around the metal ion. We suggest that lithium metasilicate has enough potential candidates to be a phosphor material.     

Preparation and photocatalytic degradation of erbium doped titanium dioxide nanorods

Photocatalytic degradation of methylene blue (MB) in water was examined using Er³⁺-doped TiO₂ (Er–TiO₂) nanorods prepared by a sol–gel derived electrospinning, calcination, and subsequent mechanical grinding. Different concentrations of Er dopant in the range of 0–1.0 mol% were synthesized to evaluate the effect of Er content on the photocatalytic activity of TiO₂. Among Er³⁺–TiO₂ catalysts, the 0.7 mol% Er³⁺–TiO₂ catalyst showed the highest MB degradation rate. The degradation kinetic constant (k) increased from 1.0 × 10^?3 min^?1 to 5.1 × 10^?3 min^?1 with the increase of Er³⁺ doping from 0 to 0.7 mol%, but decreased down to 2.1 × 10^?3 min^?1 when Er³⁺ content was 1.0 mol%. It can be concluded that the degradation of MB under UV radiation was more efficient with Er³⁺–TiO₂ catalyst than with pure TiO₂. The higher activity might be attributed to the transition of 4f electrons of Er³⁺ and red shifts of the optical absorption edge of TiO₂ by erbium ion doping.     

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).     

Erbium-doped lead silicate glass for near-infrared emission and temperature-dependent up-conversion applications

Erbium-doped lead silicate glass has been investigated for near-infrared emission and up-conversion applications. Near-infrared emission due to ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ is relatively broad (70.5 nm) and long-lived (3.7 ms). Also, up-conversion luminescence spectra of Er³⁺ ions in lead silicate glass have been examined as a function of temperature. The relative intensities of luminescence bands corresponding to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ were determined with temperature. The fluorescence intensity ratio and temperature sensitivity were calculated. The maximum sensitivity for Er³⁺ doped lead silicate glass is close to 26.4 × 10^?4 K^?1 at T = 590 K.     

Excited states dynamics of Er3+ in Sc2O3 ceramic

The spectral characteristics of Er³⁺ in Sc₂O₃ transparent ceramics are presented. The Er³⁺ visible spectra in the ceramics, prepared by solid-state synthesis, show only lines that could be assigned to C₂ sites. The Stark energy levels, cross-sections and emission kinetics of levels involved in the green upconversion emission under infrared excitation in the 800 nm range were determined. The green upconversion emission (²H_11/2, ⁴S_3/2)→⁴I_15/2 characteristics under excitation with a pulsed Ti:sapphire laser in (⁴I_15/2→⁴I_9/2) absorption were analyzed. The emission kinetics reveal a competition of two-step (⁴I_15/2→⁴I_9/2)+(⁴I_9/2→²H_9/2) excited state absorption (ESA) and (⁴I_11/2, ⁴I_15/2)→(⁴I_11/2, ⁴F_7/2) energy transfer upconversion (ETU) processes function on the excitation wavelength.