Preparation and upconversion property of TeO2:Er/Yb nanoparticles

Different crystal structure of TeO₂ nanoparticles were used as the host materials to prepare the Er³⁺/Yb³⁺ ions co-doped upconversion luminescent materials. The TeO₂ nanoparticles mainly kept the original morphology and phase after having been co-doped the Er³⁺/Yb³⁺ ions. All the as-prepared TeO₂:Er³⁺/Yb³⁺ nanoparticles showed the green emissions (525 nm, 545 nm) and red emission (667 nm) under 980 nm excitation. The green emissions at 525 nm, 545 nm and red emission at 667 nm were attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions, respectively. For the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, three-photon process involved in the green (²H_11/2 → ⁴I_15/2) emission, while two-photon process involved in the green (⁴S_3/2→⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. For the β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles, two-photon process involved in the green (²H_11/2 → ⁴I_15/2), green (⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_15/2) emissions. It suggested that the crystal structure of TeO₂ nanoparticles had an effect on transition processes of the Er³⁺/Yb³⁺ ions. The emission intensities of the α-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles and β-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles were much stronger than those of the (α + β)-TeO₂:Er³⁺/Yb³⁺ (3/10 mol%) nanoparticles.     

Erbium (Er) containing perfluorosulfonic polymer film with high photoluminescence quantum yield

Novel erbium (Er³⁺) containing perfluorosulfonic polymer Nafion films were prepared by spinning-coating and dripping method. The Er³⁺ ions were bonded to Nafion by the coordination to Er³⁺ of sulphonic groups. The refractive index of the film with a thickness of 2 μm is 1.3631 at 1315 nm. The thermal and photoluminescence properties of the films were investigated by the thermogravimetric analysis (TGA) and photoluminescence spectra. It was found that the films have high thermal stability. In the photoluminescence investigation, the films heated at 300 °C have typical emission around 1535 nm due to the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ and longer luminescence lifetimes. The highest NIR PL quantum efficiency was found to be 0.4%, which is about 20 times higher than the usual erbium organic complexes with the hydrogen-containing ligands.     

Hydrothermal synthesis and luminescence properties of octahedral LiYbF4: Er microcrystals

LiYbF₄: Er³⁺ octahedral microcrystals have been successfully prepared through a facile hydrothermal method assisted with EDTA (ethylenediaminetetraacetic acid). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric and differential scanning calorimeters (TG-DSC), photoluminescence (PL) spectra are used to characterize the samples. Under 976 nm excitation, the upconversion (UC) luminescence emission spectra of LiYbF₄: Er³⁺ microcrystals show the characteristic Er³⁺ emissions. The results show that the infrared light emissions at 792 nm of ⁴I_9/2 → ⁴I_15/2 are dominantly strong unusually, while the green emissions at 526 and 545 nm assigned to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2, respectively, and the red emission at 667 nm of ⁴F_9/2→⁴I_15/2 are relatively weaker. Most importantly, the samples show more efficient luminescence with further heat treatment.     

Infrared to visible upconversion luminescence in Er/Yb co-doped CeO2 inverse opal

Infrared to visible upconversion luminescence has been investigated in Er³⁺/Yb³⁺ co-doped CeO₂ inverse opal. Under the excitation of 980 nm diode lasers, visible emissions centered at 525, 547, 561, 660 and 680 nm are observed, which are assigned to the Er³⁺ transitions of ²H_11/2 → ⁴I_15/2 (525 nm), ⁴S_3/2 → ⁴I_15/2 (547, 561 nm), ⁴F_9/2 → ⁴I_15/2 (660 and 680 nm), respectively. The effect of photonic band gap on the upconversion luminescence intensity was also obtained. Additionally, the upconversion luminescence mechanism was studied. The dependence of Er³⁺ upconversion emission intensity on pump power reveals that it is a two-photon excitation process.     

Growth of silver nano-particle embedded in tellurite glass: Interaction between localized surface plasmon resonance and Er ions

In this paper we show a systematic study of the growth of silver nano-particles (NPs) embedded in an Erbium-doped tellurite glass with annealing time, aiming to a photoluminescence enhancement. The results indicate an improved or quenching of the photoluminescence due to an energy transfer mechanism in the coupling between NP’s electric dipoles and Er⁺³ transitions (⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 and ⁴I_13/2 → ⁴I_15/2).     

Sol-gel synthesis and green upconversion luminescence in BaGd2(MoO4)4:Yb,Er phosphors

Yb³⁺/Er³⁺ codoped BaGd₂(MoO₄)₄ phosphor powders were prepared by the Sol-gel method and the upconversion luminescence properties were investigated in detail. Under 980 nm semiconductor laser excitation, BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor exhibits green upconversion luminescence with peaks at 530 and 550 nm, which are due to the transitions of Er³⁺ (²H_11/2) → Er³⁺ (⁴I_15/2) and Er³⁺ (⁴S_3/2) → Er³⁺ (⁴I_15/2), respectively. Both of the two green emission lines are produced by populating Er³⁺ ions to the excited state through a two-photon process. By monitoring the intensities of the green upconversion luminescence, the optimum conditions for the Sol-gel synthesis were determined when the molar ratio of citric acid to total chelate metal cations was 2:1 and the sintering temperature was at 1073 K. The concentration quenching effect for Er³⁺ was found at the optimum doping concentration of 6 mol%, and the critical distance for the neighboring Er³⁺ was determined to be about 21.5 Å.     

Bright white upconversion luminescence from Er-Tm-Yb doped CaSnO3 powders

Bright white upconversion luminescence from Er³⁺-Tm³⁺-Yb³⁺ doped CaSnO₃ powders is obtained under the diode laser excitation of 980 nm. It is composed of three primary colors of red, green and blue emissions, which originate from the transitions of ⁴F_9/2 → ⁴I_15/2, (²H_11/2, ⁴S_3/2) → ⁴I_15/2 of Er³⁺ ions and ¹G₄ → ³H₆ of Tm³⁺ ions, respectively. The efficient upconversion emission is attributed to the energy transfer between Yb³⁺ and Er³⁺ or Tm³⁺ions. Moreover, it is observed that Tm³⁺ acts as the quenching center for the green upconversion luminescence from Er³⁺ ions, and the sensitizer for the red and blue luminescence when the Tm³⁺ doping content is less than 0.3 mol%. This is interpreted in terms of the efficient energy transfer between Tm³⁺ and Er³⁺ ions. The calculated color coordinates fall within the white region in the standard 1931 CIE chromaticity diagram, indicating the potential applications of Er³⁺-Tm³⁺-Yb³⁺ doped CaSnO₃ in the field of displaying and lasers, etc.     

Er related 1.53 μm emission from Er-Si-codoped ZnO multilayer film prepared by rf-sputtering

The near-infrared emission from Er and Si codoped ZnO film, synthesized by cosputtering from separated Er, Si, and ZnO targets, has been investigated. By building the multilayer film structure, controlling the Er concentration, and optimizing the annealing condition, the intensity of Er³⁺ related 1.53 μm photoluminescence (PL), which originates from the transition of Er³⁺: ⁴I_13/2 → ⁴I_15/2, can be modulated. It is shown that the maximum intensities of Er³⁺ related 1.53 μm PL are obtained when the Si:ZnO/Er:Si:ZnO/Si:ZnO sandwiched multilayer film and the alternate Er:ZnO/Si:ZnO multilayer film were annealed at 1000 °C and 950 °C, respectively. The Er³⁺ related 1.54 μm PL intensity of the multilayer film is higher than that of the Er:ZnO monolayer film. This can be attributed to the presence of the silicon nanocrystals that could act as sensitizers of Er³⁺ ions in the multilayer film. The PL of the sandwiched multilayer film and the alternate multilayer film were measured under different temperatures (15-300 K). The sandwiched multilayer film exhibits a nonmonotonic temperature dependence as well as the alternate multilayer film, which differs from that of Er-doped ZnO as previously reported.     

Characteristics of nanocrystalline AlN:Er films co-deposited by using AlN, Er, and SiO2 targets

We report the characteristics of AlN:Er films that were co-deposited by using AlN, Er, and SiO₂ targets. The PL emission spectra show strong green emissions of Er³⁺ ions in AlN:Er films annealed at an optimal temperature of 750 °C, which is attributed to the intra-4f Er³⁺ transitions of ²H_11/2 → ⁴I_15/2 and ⁴F_7/2 → ⁴I_15/2. This optimal temperature can activate Er species as an efficient visible luminescence center. High-resolution transmission electron microscopy (HREM) observations showed that the AlN:Er film annealed at 750 °C exhibits the microstructure of AlN nanocrystallites embedded in the amorphous matrix. The occurrence of strong Er³⁺ emissions in the amorphous-nanocrystalline AlN:Er films by thermal annealing might contribute to an increased number of excitation Er³⁺ centers and the presence of oxygen related to Er³⁺ excitation and recombination processes. A distinct visible bluish green emission is also confirmed from the EL device with an amorphous-nanocrystalline AlN:Er active layer.     

Upconversion emission from Tm:Yb and Tm:Er:Yb doped Y2SiO5 powders prepared by combustion synthesis

Tm³⁺:Er³⁺:Yb³⁺ doped Y₂SiO₅ powders were prepared by combustion synthesis with estimated as-prepared weight (wt.) % concentrations of 0.25:0.0:2.0, 0.25:0.5:2.0 and 0.25:1.0:2.0, respectively. Blue (Tm³⁺: ¹G₄ → ³H₆), green (Er³⁺: ⁴S_3/2, ²H_11/2 → ⁴I_15/2) and red (Er³⁺: ⁴F_9/2 → ⁴I_15/2) upconversion (UC) emissions were observed under 975 nm infrared diode laser excitation. The UC process took place via energy transfer from Yb³⁺ to Er³⁺ and Tm³⁺ ions. The CIE chromaticity coordinates of Tm³⁺:Er³⁺:Yb³⁺ doped Y₂SiO₅ powders were investigated as a function of the diode laser power and Er³⁺ concentration.     

Transparent glass ceramic containing Er:CaF2 nano-crystals prepared by sol-gel method

Er³⁺ doped SiO₂-CaF₂ transparent glass ceramic was prepared by sol-gel method. The microstructural evolution of the samples was studied with X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared spectra (IR). After heat-treatment at 900 °C, the Si-OH bonds and other organic groups were basically eliminated. The CaF₂ crystallites in the sample heat-treated at 900 °C are 10-20 nm in size, distributed homogeneously among the amorphous silica matrix. The efficient upconversion emission for Er^3+.4F_9/2 → ⁴I_15/2 transition was recorded under 980 nm excitation, which could be ascribed to the incorporation of Er³⁺ ions into the CaF₂ nano-crystals with low phonon energy.     

Upconversion in Er-doped Gd2O3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd₂O₃ nanocrystals doped with different concentrations of Er³⁺ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions was observed with increasing Er³⁺ concentration in the Gd₂O₃ nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er³⁺ concentration was increased, the intensity of the red (⁴F_9/2 → ⁴I_15/2) emission was observed to increase more rapidly in comparison to the green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.     

Sol-gel preparation of near-infrared broadband emitting Er-doped SiO2-Ta2O5 nanocomposite films

This article reports a study on the preparation, densification process, and structural and optical properties of SiO₂-Ta₂O₅ nanocomposite films obtained by the sol-gel process. The films were doped with Er³⁺, and the Si:Ta molar ratio was 90:10. Values of refractive index, thickness and vibrational modes in terms of the number of layers and thermal annealing time are described for the films. The densification process is accompanied by OH group elimination, increase in the refractive index, and changes in film thickness. Full densification of the film is acquired after 90 min of annealing at 900 °C. The onset of crystallization and devitrification, with the growth of Ta₂O₅ nanocrystals occurs with film densification, evidenced by high-resolution transmission electron microscopy. The Er³⁺-doped nanocomposite annealed at 900 °C consists of Ta₂O₅ nanoparticles, with sizes around 2 nm, dispersed in the SiO₂ amorphous phase. The main emission peak of the film is detected at around 1532 nm, which can be assigned to the ⁴I_13/2 → ⁴I_15/2 transition of the Er³⁺ ions present in the nanocomposites. This band has a full width at half medium of 64 nm, and the lifetime measured for the ⁴I_13/2 levels is 5.4 ms, which is broader compared to those of other silicate systems. In conclusion, the films obtained in this work are excellent candidates for use as active planar waveguide.     

Synthesis and upconversion luminescence properties of Yb/Er codoped BaGd2(MoO4)4 powder

Synthesis and upconversion luminescence properties of the new BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor were reported in this paper. The phosphor powder was obtained by the traditional high temperature solid-state method, and its phase structure was characterized by the XRD pattern. Based on the upconversion luminescence properties studies, it is found that, under 980 nm semiconductor laser excitation, BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor exhibits intense green upconversion luminescence, which is ascribed to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transition of Er³⁺. While the observed much weaker red emission is due to the non-radiative relaxation process of ⁴S_3/2 → ⁴F_9/2 and ⁴F_9/2 → ⁴I_15/2 transition originating from the same Er³⁺. The concentration quenching effects for both Yb³⁺ and Er³⁺ were found, and the optimum doping concentrations of 0.5 mol% Yb³⁺ and 0.08 mol% Er³⁺ in the new BaGd₂(MoO₄)₄ Gd³⁺ host were established.     

Infrared-to-visible upconversion flurescence of Er/Yb-codoped bismuthate glasses

Er³⁺/Yb³⁺-codoped bismuthate glasses for developing potential upconversion lasers have been fabricated and characterized. The optimal Yb³⁺ doping content was investigated in the glasses with different Yb³⁺-Er³⁺ concentration ratios and the optimal Yb³⁺-Er³⁺ concentration ratio is 5:1. Under 975 nm excitation, intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation.     

The effect of In ion on the optical characteristics of Er in Er/Yb:LiNbO3 crystal

The effect of In³⁺ ion on the optical characteristics of Er³⁺ ion in Er/Yb:LiNbO₃ crystal under 980 nm excitation has been investigated. The Er and Yb contents in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES). A significant enhancement of 1.54 μm emission was observed for Er/Yb:LiNbO₃ crystal doped with 1 mol% In₂O₃. The studies on the UV-vis absorption and the OH⁻ absorption spectra indicate that the threshold concentration of In³⁺ ion decreases with the Er/Yb doping in Er/Yb/In:LiNbO₃ crystal. The 1 mol% In₂O₃ doping results in the reduction of absorption cross section in the UV-vis region, meaning the formation of Er³⁺ cluster sites. The enhancement of 1.54 μm emission is attributed to the larger probabilities of the cross relaxation processes ⁴S_3/2 + ⁴I_15/2 → ⁴I_9/2 + ⁴I_13/2 (Er), ⁴S_3/2 + ⁴I_15/2 → ⁴I_13/2 + ⁴I_9/2 (Er) and ⁴I_9/2 + ⁴I_15/2 → ⁴I_13/2 + ⁴I_13/2 (Er) induced by Er³⁺ cluster sites.     

New transparent Er-doped oxyfluoride tellurite glass ceramic with improved near infrared and up-conversion fluorescence properties

Transparent glass ceramics have been obtained by nucleation and growth of Y₂Te₆O₁₅ or Er₂Te₅O₁₃ cubic phase in a new Er³⁺-doped oxyfluoride tellurite glass. Effect of heat treatment on absorption spectra, luminescence and up-conversion properties in the oxyfluoride tellurite glass has been investigated. With heat treatment the ultraviolet absorption edge red shifted evidently for the oxyfluoride telluride glass. The near infrared emission that corresponds to Er³⁺:⁴I_13/2 → ⁴I_15/2 can be significantly enhanced after heat treatment. Under 980 nm LD pumping, red and green up-conversion intensity of Er³⁺ in the glass ceramic can be observed much stronger than that in the base glass.     

Influence of Ce on the luminescence properties of Er/Yb:YVO4 crystals

YVO₄ single crystals doped with Ce³⁺, Er³⁺ and Yb³⁺ ions were grown by the Czochralsski technology. The luminescence properties of Er³⁺/Yb³⁺:YVO₄ single crystals with different concentration of Ce³⁺ were studied, and the energy transfer mechanism between Er³⁺, Yb³⁺ and Ce³⁺ was discussed based on their energy level properties. The branching ratios of the ⁴I_11/2 → ⁴I_13/2 transition in different samples were calculated. The results indicate that codopants of Ce³⁺ greatly enhance the population rate of the ⁴I_13/2 level due to the fast resonant energy transfer between Er³⁺ and Ce³⁺, i.e., ⁴I_11/2(Er³⁺) + ²F_7/2(Ce³⁺) → ⁴I_13/2(Er³⁺) + ²F_5/2(Ce³⁺).     

Structural and optical properties of Er implanted AlN thin films: Green and infrared photoluminescence at room temperature

In this work erbium ions were implanted into AlN films grown on sapphire with fluence range: (0.5-2) × 10¹⁵ at/cm⁻², ion energy range: 150-350 keV and tilt angle: 0°, 10°, 20°, 30°. The optical and structural properties of the films are studied by means of photoluminescence and Raman spectroscopy in combination with Rutherford backscattering/channeling (RBS/C) measurements. The photoluminescence spectra of the Er³⁺ were recorded in the visible and infrared region between 9 and 300 K after thermal annealing treatments of the samples. The emission spectrum of the AlN:Er films consists of two series of green lines centered at 538 and 558 nm with typical Er³⁺ emission in the infrared at 1.54 μm. The green lines have been identified as Er³⁺ transitions from the ²H_11/2 and ⁴S_3/2 levels to the ⁴I_15/2 ground state. Different erbium centers in the matrix are suggested by the change of infrared photoluminescence relative intensity of some of the emission lines when different excitation wavelengths are used. The relative abundances of these centers can be varied by using different implantation parameters. The Raman and RBS/C measurements show good crystalline quality for all the studied films.     

Realization of modulating broadband emission from Er–Tm codoped calcium boroaluminate glasses by dual-wavelength pumping

Near-infrared photoluminescence (PL) of calcium boroaluminate (CABAL) glasses codoped with Er₂O₃ and Tm₂O₃ has been investigated by dual-wavelength pumping at 795 and 476 nm. Spectrum shape of broadband emission could be modulated by controlling the power ratio of two pumping lines (P₄₇₆/P₇₉₅). The result shows that the full width at half maximum can reach ∼500 nm in the wavelength range from 1.3 to 2.0 μm by controlling P₄₇₆/P₇₉₅ = 12. The PL spectra show four characteristic peaks located at 1.46, 1.53, 1.58 and 1.80 μm, corresponding to Tm³⁺: ³H₄ → ³F₄, Er³⁺: ⁴I_13/2 → ⁴I_15/2, Tm³⁺: ¹G₄ → ³F₂ and Tm³⁺: ³F₄ → ³H₆ emissions, respectively. The energy transfer (ET) (ET1: Er³⁺: ⁴I_13/2, Tm³⁺: ³F₄ → Er³⁺: ⁴I_15/2, Tm³⁺: ³H₄ and ET2: Er³⁺: ⁴I_13/2, Tm³⁺: ³H₆ → Er³⁺: ⁴I_15/2, Tm³⁺: ³F₄) between Er³⁺ and Tm³⁺ ions play important roles in the luminescence mechanisms. In addition, a new ET process (ET: Tm³⁺: ¹G₄, Er³⁺: ⁴F_9/2 → Tm³⁺: ³F₂, Er³⁺: ⁴F_7/2) was identified. The flat broadband emission with the bandwidth of ∼500 nm could be realized by changing P₄₇₆/P₇₉₅ as a result of the radiative transitions, Tm–Tm cross-relaxation (Tm³⁺: ³H₄, ³H₆ → Tm³⁺: ³F₄, ³F₄) and Er–Tm ET processes.