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.     

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⁺).     

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.     

Design and achieving mechanism of upconversion white emission based on Yb/Tm/Er tri-doped KY3F10 nanocrystals

KY₃F₁₀:Yb³⁺/Tm³⁺/Er³⁺ upconversion nanocrystals are synthesized via a simple hydrothermal procedure. The nanocrystals emit the near equal energy white light with high brightness and favorable color balance when excited using a 980 nm continuous wave diode laser. The research of upconversion mechanism indicates that in addition to the energy transfer processes from Yb³⁺ to Tm³⁺ and Er³⁺, respectively, there exists a new process ¹G₄ (Tm³⁺) + ⁴I_11/2 (Er³⁺) → ³H₄ (Tm³⁺) + ⁴S_3/2 (Er³⁺).     

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.     

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.     

Significant reduction of upconversion emission in CaTiO3: Yb, Er inverse opals

Inverse opal photonic crystals of Yb³⁺, Er³⁺ co-doped CaTiO₃ (CaTiO₃: Yb, Er) were prepared using self-assembled polystyrene templates combined with the infiltration of sol-gel precursor. The influence of the photonic band gap on upconversion emission of Er³⁺ has been investigated in the CaTiO₃: Yb, Er inverse opals. Significant reduction of the upconversion emission was detected if the photonic band-gap overlaps with the Er³⁺ ions emission band.     

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.     

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.     

Er:YAl3(BO3)4 glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y_1 − xEr_xAl₃(BO₃)₄ multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er^{3+ 4}I_13/2 energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 μs and 200 μs, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl₃(BO₃)₄ compounds are promising for low loss waveguides.     

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.     

White upconverted luminescence of Ho/Yb/Tm tri-doped Gd2Mo3O9 phosphors

Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors were synthesized by the high-temperature solid-state method. Under 980 nm near-infrared excitation, the white-light emission can be observed, which is consists of the blue, green, and red UC emissions. The green and red emission at 547 nm and 660 nm originated from the transition of Ho³⁺ (⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈) and the blue emission at 475 nm attributed to the transition of Tm³⁺ (⁵G₄ → ⁵H₆). In this experiment, we selected the optimum concentration ratio of the three rare earths for the bright white emission. The Commission internationale de L’Eclairage (CIE) coordinates for the samples were calculated, and chromaticity coordinates were very close to white light regions. We find that the calculated CIE color coordinates of the Yb³⁺/Tm³⁺/Ho³⁺ tri-doped Gd₂Mo₃O₉ phosphors changed with the incident pump power from 400 mW/cm² to 1000 mW/cm². The upconversion luminescence mechanism of the samples was discussed on its spectral. The white light may be proved to be a candidate material for applications in various fields.     

Polarized spectroscopic properties of Ho ions in NaLa(MoO4)2 crystal

A Ho³⁺-doped NaLa(MoO₄)₂ single crystal was grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The spontaneous emission probabilities, radiative lifetimes, and fluorescence branching ratios of the typical fluorescence multiplets of Ho³⁺ ions were calculated. The polarized stimulated emission and gain cross-sections of the ⁵I₇ → ⁵I₈ transition were obtained. The results show that the Ho³⁺:NaLa(MoO₄)₂ crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0 μm.     

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.     

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.     

Effect of vapor transport equilibration and Mg doped on the luminescence of Er:LiNbO3

Luminescence properties of the congruent and vapor transport equilibration (VTE) treated Er:LiNbO₃ and Er:Mg:LiNbO₃ crystals were recorded at room temperature. It is observed that VTE treatment could enhance the emission intensity of Er³⁺ ions and doping with MgO would weaken it in the visible spectra. As a result, the luminescence intensity of Er³⁺ ions in the VTE treated Er:Mg:LiNbO₃ crystal increased up to 2.2 times than that in the congruent Er:LiNbO₃ crystal. In addition, both VTE treatment and doping with MgO result in some changes of the relative emission intensity of some peaks in the visible emission spectra. In the infrared emission spectra, the luminescence peak at 1540 nm of Er³⁺ ions shifts towards the larger wavelength when the Er:LiNbO₃ crystals were treated using VTE or doped with MgO. The changes in crystalline environment of Er³⁺ ions due to VTE treatment or doping with Mg²⁺ play a key role in these phenomena.     

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.     

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.     

Growth and spectral properties of Er:NaGd(WO4)2 crystal

A high optical quality Er³⁺-doped NaGd(WO₄)₂ single crystal with dimensions of ∅18 × 50 mm³ has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er³⁺ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm.     

Concentration effect of Nd ion on the spectroscopic properties of Er/Nd co-doped LiYF4 single crystal

High quality Er³⁺/Nd³⁺:LiYF₄ single crystals were grown by a Bridgman method. Their spectroscopic properties were studied to understand the Nd³⁺ concentration effect upon excitation of an 800 nm laser diode. The intensest 2.7 μm emission was observed in the LiYF₄ crystal codoped with 0.99 mol% Er³⁺ and 0.62 mol% Nd³⁺. Meanwhile, the emission intensity for the green up-conversion and 1.5 μm downconversion of Er³⁺ decreased with increasing of the Nd³⁺ concentration. The modified Inokuti–Hirayama model was used to analyze the decay curves of the 1.06 (Nd³⁺) and 1.5 (Er³⁺) μm emissions. The results indicated that the energy transfer process (Er³⁺:⁴I_13/2 + Nd³⁺:⁴I_9/2 → Er³⁺:⁴I_15/2 + Nd³⁺:⁴I_15/2) is mainly due to the electric dipole–dipole interaction. The energy transfer efficiencies between Nd³⁺ and Er³⁺ ions were calculated. All results suggested that the Er³⁺/Nd³⁺:LiYF₄ single crystals may have potential applications in mid-infrared lasers.