Fabrication and Upconversion Luminescent Properties of Er3+‐Doped and Er3+/Yb3+ Codoped La2O2CN2 Nanofibers

La₂O₂CN₂:Er³⁺and La₂O₂CN₂:Er³⁺/Yb³⁺ upconversion (UC) luminescence nanofibers were successfully fabricated via cyanamidation of the respective relevant La₂O₃:Er³⁺ and La₂O₃:Er³⁺/Yb³⁺ nanofibers which were obtained by calcining the electrospun composite nanofibers. The morphologies, structures, and properties of the nanofibers are investigated. The mean diameters of La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers are 179.46 ± 12.58 nm and 198.85 ± 17.07 nm, respectively. It is found that intense green and weak red emissions around 524, 542, and 658 nm corresponding to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_l5/2 energy levels transitions of Er³⁺ ions are observed for La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers under the excitation of a 980‐nm diode laser. Moreover, the emitting colors of La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers are all located in the green region. The upconversion luminescent mechanism and formation mechanism of the nanofibers are also proposed.     

Microwave Sol–Gel Synthesis of CaGd2(MoO4)4:Er3+/Yb3+ Phosphors and Their Upconversion Photoluminescence Properties

CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ phosphors with the doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2, and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by the microwave sol–gel method, and the crystal structure refinement and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after heat‐treatment at 900°C for 16 h, showed a well‐crystallized morphology. Under the excitation at 980 nm, CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited strong 525 and 550‐nm emission bands in the green region and a weak 655‐nm emission band in the red region. The Raman spectrum of undoped CaGd₂(MoO₄)₄ revealed about 15 narrow lines. The strongest band observed at 903 cm^?1 was assigned to the ν₁ symmetric stretching vibration of MoO₄ tetrahedrons. The spectra of the samples doped with Er and Yb obtained under 514.5 nm excitation were dominated by Er³⁺ luminescence preventing the recording Raman spectra of these samples. Concentration quenching of the erbium luminescence at ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions in the CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ crystal structure was established to be approximately at the 10 at.% doping level.     

Optimization of sensitizer concentration for upconversion photoluminescence of Yb3+/Er3+: La10W22O81 nanophosphor rods

Yb³⁺/Er³⁺codoped La₁₀W₂₂O₈₁ (LWO) nanophosphor rods have been successfully synthesized by a facile hydrothermal assisted solid state reaction method, and their upconversion photoluminescence properties were systematically studied. X-ray diffraction patterns revealed that the nanophosphors have an orthorhombic structure with space group Pbcn (60). A microflowers-like morphology with irregular hexagonal nanorods was observed using field emission scanning electron microscopy for the Yb³⁺(2 mol%)/Er³⁺(2 mol%):LWO nanophosphor. The shape and size of the nanophosphor and the elements along with their ionic states in the material were confirmed by TEM and XPS studies, respectively. A green upconversion emission was observed in the Er³⁺: LWO nanophosphors under 980 nm laser excitation. A significant improvement in upconversion emission has been observed in the Er³⁺: LWO nanophosphors by increasing the Er³⁺ ion concentration. A decrease in the upconversion emission occurred due to concentration quenching when the doping concentration of Er³⁺ ions was greater than 2 mol%. An optimized Er³⁺(2 mol%): LWO nanophosphor exhibited a strong near infrared emission at 1.53 μm by 980 nm excitation. The green upconversion emission of Er³⁺(2 mol%): LWO was remarkably enhanced by co-doping with Yb³⁺ ions under 980 nm excitation because of energy transfer from Yb³⁺ to Er³⁺. The naked eye observed this upconversion emission when co-doping with 2 mol% Yb³⁺. In order to obtain the high upconversion green emission, the optimized sensitizer concentration of Yb³⁺ ions was found to be 2 mol%. The upconversion emission trends were studied as a function of stimulating laser power for an optimized sample. Moreover, the NIR emission intensity has also been enhanced by co-doping with Yb³⁺ ions due to energy transfer from Yb³⁺ to Er³⁺. The energy transfer dynamics were systematically elucidated by energy level scheme. Colorimetric coordinates were determined for Er³⁺ and Yb³⁺/Er³⁺: LWO nanophosphors. The energy transfer mechanism was well explained and substantiated by several fluorescence dynamics of upconversion emission spectra and CIE coordinates. The results demonstrated that the co-doped Yb³⁺(2 mol%)/Er³⁺(2 mol%): LWO nanophosphor material is found to be a suitable candidate for the novel upconversion photonic devices.     

Blue Upconversion Emission in Germanate Glass Co-Doped with Yb3+/Tm3+ Ions

In the paper, the upconversion luminescence of 70GeO₂–30[Ga₂O₃–BaO–Na₂O] glass system co-doped with Yb³⁺/Tm³⁺ ions was investigated. Strong blue emission at 478 nm corresponding to the transition ¹G₄ → ³H₆ in thulium ions was measured under the excitation of 976-nm diode laser. The dependence of the upconversion emission upon the thulium ion concentration was studied to determine the optimal conditions of energy transfer between energy levels of active dopants. The most effective energy transfer Yb³⁺ → Tm³⁺ was obtained in glass co-doped with molar ratio of dopant 0.7 Yb₂O₃/0.07 Tm₂O₃. The increase in thulium concentration more than 0.07 mol% results in the reverse energy transfer from Tm³⁺ → Yb³⁺, which leads to rapid quenching of the luminescence line at the wavelength 478 nm. In germanate glass co-doped with 0.7Yb₂O₃/0.07Tm₂O₃, the longest lifetime of ¹G₄ level equal 278 μs was achieved. The presented results indicate that elaborated germanate glass co-doped with Yb³⁺/Tm³⁺ ions is a promising material that can be used to produce fiber lasers and superluminescent fiber sources generating radiation in the visible spectrum.     

A broadband-sensitive upconverter: Garnet-type Ca3Ga2Ge3O12 codoped with Er3+, Y3+, Li+, Ni2+, and Nb5+

We have developed a new broadband-sensitive photon upconversion (UC) material that can be used for transparent ceramic plates mounted on the rear faces of crystalline silicon solar cells. We selected the host material of a cubic crystal structure codoped with Er³⁺ and Ni²⁺ so that the Ni²⁺ dopants were fully activated to sensitize the Er³⁺ emitters. In garnet-type Ca₃Ga₂Ge₃O₁₂ with additional codopants of Nb⁵⁺ and Li⁺ for charge compensation, all the Ni²⁺ dopants occupied the six-coordinated Ga³⁺ sites, leading to highly efficient energy transfer from the Ni²⁺ to the Er³⁺. Formation of four-coordinated Ni²⁺ that quenches the UC emission of the Er³⁺ was prevented, because Ni²⁺ cannot substitute the four-coordinated Ge⁴⁺ much smaller than Ni²⁺. Consequently, energy dissipation from the Er³⁺ to the Ni²⁺ was well reduced compared with the previously developed Gd₃Ga₅O₁₂:Er,Ni,Nb in which the Ni²⁺ dopants partially occupied the four-coordinated Ga³⁺ sites. Additional introduction of Y³⁺ and Li⁺ enhanced optical transitions and improved the UC performance, owing to more enhanced lattice distortion, along with eliminating different phases. The optimal composition (Ca_0.6Er_0.1Y_0.1Li_0.2)₃(Ga_0.98Ni_0.01Nb_0.01)₂Ge₃O₁₂ exhibited a broadband sensitivity ranging from 1.1 μm (the absorption edge of silicon) to 1.6 μm for the UC emission at 0.98 μm.     

Upconversion luminescence properties of NaBi(MoO4)2:Ln3+, Yb3+ (Ln = Er,Ho) nanomaterials synthesized at room temperature

Studies on lanthanide ions doped upconversion nanomaterials are increasing exponentially due to their widespread applications in various fields such as diagnosis, therapy, bio-imaging, anti-counterfeiting, photocatalysis, solar cells and sensors, etc. Here, we are reporting upconversion luminescence properties of NaBi(MoO₄)₂:Ln³⁺, Yb³⁺ (Ln = Er, Ho) nanomaterials synthesized at room temperature by simple co-precipitation method. Diffraction and spectroscopic studies revealed that these nanomaterials are effectively doped with Ln³⁺ ions in the scheelite lattice. DR UV–vis spectra of these materials exhibit two broad bands in the range of 200–350 nm correspond to MoO₄²⁻ charge transfer, s-p transition of Bi³⁺ ions and sharp peaks due to f-f transition of Ln³⁺ ions. Upconversion luminescence properties of these nanomaterials are investigated under 980 nm excitation. Doping concentration of Er³⁺ and Yb³⁺ ions is optimized to obtain best upconversion photoluminescence in NaBi(MoO₄)₂ nanomaterials and is found to be 5, 10 mol % for Er³⁺, Yb³⁺, respectively. NaBi(MoO₄)₂ nanomaterials co-doped with Er³⁺, Yb³⁺ exhibit strong green upconversion luminescence, whereas Ho³⁺, Yb³⁺ co-doped materials show strong red emission. Power dependent photoluminescence studies demonstrate that emission intensity increases with increasing pump power. Fluorescence intensity ratio (FIR) and population redistribution ability (PRA) of ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ increases with increasing the Yb³⁺ concentration. Also, these values increase linearly with increasing the pump power up to 2 W. It reveal that these thermally coupled energy levels are effectively redistributed in co-doped samples due to local heating caused by Yb³⁺.     

Ultrasensitive optical thermometer based on abnormal thermal quenching Stark transitions operating beyond 1500 nm

Light with wavelength longer than 1500 nm has great potential to afford deep bio-tissue penetration due to its extremely weak photon scattering and undetectable autofluorescence in vivo. Here, in order to satisfy the requirements for thermometry during the tumor hyperthermia process, an ultrasensitive optical thermometer operating beyond 1500 nm is developed by employing the thermally coupled Stark sublevels of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition based on fluorescence intensity ratio (FIR) technology in Yb³⁺ and Er³⁺ codoped BaY₂O₄. Compared with the typical upconversion (UC) material β-NaYF₄: Yb³⁺/Er³⁺ and Y₂O₃: Yb³⁺/Er³⁺, BaY₂O₄: Yb³⁺/Er³⁺ shows more intense red Er³⁺: ⁴F_9/2 → ⁴I_15/2 transition and 1.5 μm near-infrared (NIR) Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition induced by its larger phonon energy and higher quenching concentration of Er³⁺. An equivalent four-level model is proposed to investigate the temperature characteristics of the NIR emission, from which four Stark transitions are separated from the raw spectra, named α, β, γ, and δ respectively. Then, the NIR thermal sensing performance have been developed by utilizing the FIR of I_β to I_α and I_γ to I_α. More importantly, an ultra-high sensitivity for optical thermometry has been obtained through the combination of transition β and γ, especially in the physiological temperature region. Furthermore, the detection depth of NIR light in bio-tissues is assessed by an ex vivo test, demonstrating that the maximal detection depth of NIR emission can reach to 8 mm without any influence on optical thermometry. These findings indicate that Yb³⁺ and Er³⁺ codoped BaY₂O₄ is a remarkable contender for optical thermometry in deep tissue with ultra-high sensitivity.     

Glass-forming regions and enhanced 2.7 μm emission by Er3+ heavily doping in TeO2–Ga2O3–R2O (or MO) glasses

Er³⁺-doped fiber lasers operating at 2.7 μm have attracted increasing interest because of their various important applications; however, the intrinsic self-terminating effect of Er³⁺ and the reliability of glass hosts hindered the development of Er³⁺-doped fiber lasers. Herein, the glass-forming regions of a series TeO₂–Ga₂O₃–R₂O (or MO) (R = Li, Na, and Rb; M = Mg, Sr, Ba, Pb, and Zn) glasses are predicted by the thermodynamic calculation method. On this basis, the physical and optical properties of TeO₂–Ga₂O₃–ZnO (TGZ) glass are investigated in detail as an example. Under the excitation of 980 nm laser diode, the fluorescence intensity at 2.7 μm reaches a maximum in the heavily Er³⁺-doped TGZ glass. By contrast, the accompanying near-infrared fluorescence at 1.5 μm and upconversion green emissions at 528 nm and 546 nm are all effectively weaken. Furthermore, the lifetime gap between the ⁴I_11/2 upper laser level and ⁴I_13/2 lower laser level is sharply narrowed from 2.81 ms to 0.59 ms, which is beneficial to overcome the population conversion bottleneck. All results demonstrate that these newly developed ternary tellurite glass systems are promising candidates for near-/mid-infrared laser glass fiber, fiber amplifiers, and fiber lasers.     

Intense upconversion luminescence and energy‐transfer mechanism of Ho3+/Yb3+ co‐doped SrLu2O4 phosphor

A series of novel SrLu₂O₄: x Ho³⁺, y Yb³⁺ phosphors (x=0.005‐0.05, y=0.1‐0.6) were synthesized by a simple solid‐state reaction method. The phase purity, morphology, and upconversion luminescence were measured by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The doping concentrations and sintering temperature were optimized to be x=0.01, y=0.5 and T=1400°C to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the SrLu₂O₄:Ho³⁺, Yb³⁺ phosphors exhibit intense green upconversion (UC) emission band centered at 541 nm (⁵F₄,⁵S₂→⁵I₈) and weak red emission peaked at 673 nm (⁵F₅→⁵I₈). Under different pump‐power excitation, the UC luminescence can be finely tuned from yellow‐green to green light region to some extent. Based on energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the analysis of pump‐power dependence and luminescence decay curves. The energy‐transfer mechanisms for green and red UC emissions can be determined to be two‐photon absorption processes. Compared with commercial NaYF₄:Er³⁺, Yb³⁺ and common Y₂O₃:Ho³⁺, Yb³⁺ phosphors, the SrLu_1.49Ho_0.01Yb_0.5O₄ sample shows good color monochromaticity and relatively high UC luminescence intensity. The results imply that SrLu₂O₄:Ho³⁺, Yb³⁺ can be a good candidate for green UC material in display fields.     

Optical temperature sensor based on upconversion luminescence of Er3+ doped GdTaO4 phosphors

For the development of optical temperature sensor, a series of GdTaO₄ phosphors with various Er³⁺-doping concentrations (0, 1, 5, 10, 25, 35, 50 mol%) were synthesized by a solid-state reaction method. The monoclinic crystalline structure of the prepared samples was determined by X-ray diffraction (XRD). Under excitations of 980 and 1550 nm lasers, the multi-photon-excited green and red upconversion (UC) luminescence emissions of Er³⁺ were studied, and the critical quenching concentration of Er³⁺-doped GdTaO₄ phosphor was derived to be 25 mol%. By changing the pump power of laser, it was found that the two-photon and three-photon population processes happened for the UC emissions of Er³⁺-doped GdTaO₄ phosphors excited by 980 and 1550 nm lasers, respectively. Furthermore, based on the change of thermo-responsive green UC luminescence intensity corresponding to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ with temperature, the optical temperature sensing properties of Er³⁺-doped GdTaO₄ phosphor were investigated under excitations of 980 and 1550 nm lasers by using the fluorescence intensity ratio (FIR) technique. It was obtained that the maximum absolute sensitivity (S_A) and relative sensitivity (S_R) of Er³⁺-doped GdTaO₄ phosphors are as high as 0.0041 K⁻¹ at 475 K and 0.0112 K⁻¹ at 293 K, respectively. These significant results suggest that the Er³⁺-doped GdTaO₄ phosphors are a promising candidate for optical temperature sensor.     

Upconverting luminescence based dual-modal temperature sensing for Yb3+/Er3+/Tm3+: YF3 nanocrystals embedded glass ceramic

Yb³⁺/Er³⁺/Tm³⁺ doped transparent glass ceramic containing orthorhombic YF₃ nanoparticles was successfully synthesized by a melt-quenching method. After glass crystallization, tremendously enhanced (about 5000 times) upconversion luminescence, obvious Start-splitting of emission bands as well as long upconversion lifetimes of Er³⁺/Tm³⁺ confirmed the incorporation of lanthanide activators into precipitated YF₃ crystalline environment with low phonon energy. Furthermore, temperature-dependent upconversion luminescence behaviors of glass ceramic were systematically investigated to explore its possible application as optical thermometric medium. Impressively, both fluorescence intensity ratio of Er³⁺: ²H_11/2 → ⁴I_15/2 transition to Er³⁺: ⁴S_3/2 → ⁴I_15/2 one and fluorescence intensity ratio of Tm³⁺: ³F_2,3 → ³H₆ transition to the combined Tm³⁺: ¹G₄ → ³F₄/Er³⁺: ⁴F_9/2 → ⁴I_15/2 ones were demonstrated to be applicable as temperature probes, enabling dual-modal temperature sensing. Finally, the thermal effect induced by the irradiation of 980 nm laser was found to be negligible in the glass ceramic sample, being beneficial to gain intense and precise probing signal and detect temperature accurately.     

Efficient near-infrared to visible and ultraviolet upconversion in polycrystalline BiOCl:Er3+/Yb3+ synthesized at low temperature

Er³⁺/Yb³⁺ co-doped BiOCl poly-crystals were synthesized by the conventional solid state method at 500 °C, which exhibited good crystalline and low phonon energy. Under 980 nm excitation, the samples showed intense red upconversion (UC) luminescence (Er³⁺: ⁴F_9/2→⁴I_15/2) as well as other four UC emission bands, including ultraviolet (UV) emission at 380 nm, violet emission at 411 nm, green UC emissions at 525 and 545 nm and near-infrared (NIR) emission between 800 and 850 nm, corresponding to the transitions of ⁴G_11/2, ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴I_9/2→⁴I_15/2 of Er³⁺, respectively. Interestingly, including the violet and green UC emissions, the red one originated a nearly three-photon process in this system, and a possible UC mechanism was proposed for the enhanced red emission.     

Evolution of Strong Red Upconversion Luminescence in Er3+‐Containing Oxy‐Fluoride Glass and Glass‐Ceramics

The Er³⁺ concentration dependencies of upconversion luminescence in oxy‐fluoride glass and glass‐ceramics containing PbF₂ nanocrystals were investigated. Strong red emission from the ⁴F_9/2 → ⁴I_15/2 transition was observed with the addition of ~0.8 mol% Er³⁺ ions, whereas ~10 mol% of Er³⁺ is required to achieve such emission in several other crystalline hosts. Intensities of red emission further increased with the formation of nanocrystals through heat treatment. The Er³⁺ ions enriched in glass and segregated preferentially inside the PbF₂ nanocrystals that decreased the distance among Er³⁺ ions and thereby facilitated energy transfer.     

A Novel Multifunctional Upconversion Phosphor: Yb3+/Er3+ Codoped La2S3

Yb³⁺/Er³⁺ codoped La₂S₃ upconversion (UC) phosphors have been synthesized using high‐temperature solid‐state method. Under 971‐nm excitation, the maximum luminescence power can reach 0.64 mW at the excitation power density of 16 W/cm² and an absolute power yield of 0.36% was determined by an absolute method at the excitation power density of 3 W/cm², and the quantum yield of La₂S₃:Yb³⁺, Er³⁺ (green ~0.18%, red ~0.03%, integration ~0.21) was comparable to that of NaYF₄:Yb³⁺, Er³⁺ nanocrystals (integration ~0.005–0.30). Frequency upconverted emissions from two thermally coupled excited states of Er³⁺ were recorded in the temperature range 100–900 K. The maximum sensitivity of temperature sensing is 0.0075 K^?1. As the excitation power density increases, the temperature of host materials rapidly rises and the top temperature can reach to 600 K. Given the intense UC emission, high sensitivity, as well as good photothermal stability, La₂S₃:Yb³⁺/Er³⁺ phosphor can become a promising composite material for photothermal ablation of cancer cells possessing the functions of temperature sensing and in vivo imaging.     

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er³⁺, Tm³⁺ and Yb³⁺ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm^{3+ 1}G₄→³H₆ transition, 531 and 547 nm (green) from the Er^{3+ 2}H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions, and 640 and 662 nm (red) from the Er^{3+ 4}F_9/2 → ⁴I_15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er₂O₃, 0.5 mol% Tm₂O₃ and 2.0 mol% Yb₂O₃, and this crystal is suitable for use in highly efficient white light emission devices.     

Color-tunable up-conversion luminescence of Zn(AlxGa1-x)2O4:Yb3+,Tm3+,Er3+ powders

Color-tunable up-conversion powder phosphors Zn(Al_xGa_1-x)₂O₄: Yb³⁺,Tm³⁺,Er³⁺ were synthesized via high temperature solid-state reaction. Also, the morphological and structural characterization, up-conversion luminescent properties were all investigated in this paper. In brief, under the excitation of a 980?nm laser, all powders have same emission peaks containing blue emission at 477?nm (attributed to ¹G₄→³H₆ transition of Tm³⁺ ions), green emission at 526?nm and 549?nm (attributed to ²H_11/2→ ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions respectively), red emission at about 659?nm and 694?nm (attributed to ⁴F_9/2→⁴I_15/2 transition of Er³⁺ ions and ³F₃→³H₆ transition of Tm³⁺ ions, respectively), which are not changed after the doping of Al³⁺ ions. However, the doping of Al³⁺ ions can enhance the up-conversion luminescent intensity and efficiency, while the emission color of as-prepared powder phosphors can be tunable by controlling the doping amount of Al³⁺ ions. Taking Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er as the cut-off value, the emissions have clear blue-shift firstly and then show obvious red-shift with the increasing doping of Al³⁺ ions. Stated thus, pink emission in ZnAl₂O₄:Yb,Tm,Er, purplish pink emission in ZnGa₂O₄:Yb,Tm,Er and Zn(Al_0.9Ga_0.1)₂O₄:Yb,Tm,Er, purple emission in Zn(Al_0.1Ga_0.9)₂O₄:Yb,Tm,Er and Zn(Al_0.3Ga_0.7)₂O₄:Yb,Tm,Er, purplish blue emission in Zn(Al_0.7Ga_0.3)₂O₄:Yb,Tm,Er, blue emission in Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er can be observed, which confirm the potential applications of as-prepared Zn(Al_xGa_1-x)₂O₄:Yb³⁺,Tm³⁺,Er³⁺ powder phosphors in luminous paint, infrared detection and so on.     

Bright red upconversion luminescence from Er3+ and Yb3+ co-doped ZnO-TiO2 composite phosphor powder

ZnO-TiO₂ composites co-doped with Er³⁺ and Yb³⁺ ions were successfully synthesized by powder-solution mixing method and their upconversion (UC) luminescence was evaluated. The effect of firing temperature, ZnO/TiO₂ mixing ratio, and dopant concentration ranges on structural and UC luminescence properties was investigated. The crystal structure of the product was studied and calculated in detail by means of X-ray diffraction (XRD). Also, the site preference of Er³⁺ and Yb³⁺ ions in the host material was considered and analyzed based on XRD results and UC luminescence characteristics. Brightest UC luminescence was observed in the ZnO-TiO₂:Er³⁺,Yb³⁺ phosphor fired at 1300 °C in which the system consisted of mixed phases; Zn₂TiO₄, TiO₂, RE₂Ti₂O₇ and RE₂TiO₅ (RE = Er³⁺ and/or Yb³⁺). Under the excitation of a 980 nm laser, the two emission bands were detected in the UC emission spectrum, weak green band centered at 544 and 559 nm, and strong red band centered at 657 and 675 nm wavelengths in accordance with ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively. The simple chemical formula equations, for explaining the site preference of Er³⁺ and Yb³⁺ ions in host crystal matrix, were generated by considering the Zn₂TiO₄ crystal structure, its crystal properties, and the effect of Er³⁺ and Yb³⁺ ions to the host crystal matrix. The UC emission intensity of the products was changed by varying ZnO/TiO₂ mixing ratios, and Er³⁺ and Yb³⁺ concentrations. The best suitable condition for emitting the brightest UC emission was 1ZnO:1TiO₂ doped with 3 mol% Er³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h.     

Preparation,Structure, and Up‐Conversion Luminescence of Yb3+/Er3+ Codoped SrIn2O4 Phosphors

SrIn₂O₄, which shows lower phonon energy than CaIn₂O₄, is not only a good photocatalyst but also can be an excellent up‐conversion (UC) host to exhibits UC luminescence. In this work, Yb³⁺ and/or Er³⁺ doped SrIn₂O₄ phosphors were synthesized, and their UC luminescence properties were studied and compared with those in the CaIn₂O₄ host. The structure of SrIn₂O₄: 0.01Er³⁺ and SrIn₂O₄: 0.1Yb³⁺/0.01Er³⁺ samples were refined by the Rietveld method and found to that SrIn₂O₄: 0.1Yb³⁺/0.01Er³⁺ showed increasing unit cell parameters and cell volume, indicating In³⁺ sites were substituted successfully by Yb³⁺ and/or Er³⁺ ions. From the UC luminescence spectra and diffuse reflection spectra, Er³⁺‐doped SrIn₂O₄ showed very weak luminescence due to ground state absorption of Er³⁺; Yb³⁺/Er³⁺ codoped SrIn₂O₄ presented strong green (550 nm) and red (663 nm) UC emissions which were assigned to energy transfer from Yb³⁺ transition ²F_7/2→²F_5/2 to the Er³⁺ transition ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2. Comparing with CaIn₂O₄, Yb³⁺/Er³⁺ codoped SrIn₂O₄ showed obvious advantages with higher UC luminescent intensity. The pumping powers study showed that UC emissions in Yb³⁺/Er³⁺ codoped SrIn₂O₄ were attributed to energy transfer of Yb³⁺→Er³⁺ with a two‐photon process. The possible UC luminescent mechanism of Yb³⁺/Er³⁺‐doped SrIn₂O₄ was discussed.     

Influence of Cr3+ on yellowish-green UC emission and energy transfer of Er3+/Cr3+/Yb3+ tri-doped zinc silicate glasses

In this paper, we study the influence of Cr³⁺ on yellowish-green upconversion (UC) emission and the energy transfer (ET) of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ (SZNL) zinc silicate glasses under excitation of the 980 nm laser diode (LD). The influence of Cr³⁺ on enhancing the red UC emission of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses under the excitation of 980nm LD was also investigated. The ET processes between Yb³⁺, Cr^3+, and Er³⁺, together with the combination of Yb³⁺-Cr³⁺-Er³⁺, which led to the green UC emission intensity of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses bands centered at ~546 nm have been significantly enhanced. By increasing the concentration of Cr³⁺ from 0 up to 5 mol.%, we can locate the Commission Internationale de l'éclairage (CIE) 1931 (x; y) chromaticity coordinates for UC emissions of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in the central position of the yellowish-green color region of CIE 1931 chromaticity diagram. Besides, the ET processes between the Yb³⁺, Cr³⁺, and Er³⁺ are also proposed and discussed.