Single colour luminescence In R3+/Yb3+/W6+(R=Tm,Ho, Er)-Doped ZrO2 Nanoparticles

ABSTRACT

Under 975?nm excitation, the Tm³⁺/Yb³⁺/W⁶⁺, Ho³⁺/Yb³⁺/W⁶⁺, and Er³⁺/Yb³⁺/W⁶⁺ doped ZrO₂ nanoparticles can emit single-colour up-conversion luminescence with high purity. The colour-purity of the three samples are 82%, 93% and 97%, respectively. The strong single-colour up-conversion emission is due to the Yb³⁺-[WO₄]^2? dimer. The energy transfers of GSA(|²F_7/2, ¹A₁>→|²F_5/2, ¹A₁>) and ESA(|²F_5/2, ¹A₁>→|²F_7/2, ¹T₁/¹T₂>) play a key role in the up-conversion population processes. The research will be helpful for luminescence labelling, luminescence imaging and colour display domains.     

Synthesis and luminescence properties of Yb3+–Er3+ co-doped LaOCl nanobelts via electrospinning combined with chlorination technique

LaOCl:Yb³⁺, Er³⁺ nanobelts were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Yb³⁺, Er³⁺ nanobelts were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that width of LaOCl:Yb³⁺, Er³⁺ nanobelts was 6.12 ± 0.18 μm under the 95% confidence level, and the thickness was 113 nm. Transmission electron microscope observation showed that as-obtained LaOCl:Yb³⁺, Er³⁺ nanobelts were composed of nanoparticles. LaOCl:Yb³⁺, Er³⁺ nanobelts emitted strong green and red up-conversion emission centring at 523, 551 and 667 nm, respectively, attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_l5/2 transitions of Er³⁺ under the excitation of a 980-nm diode laser (DL) excitation. Moreover, the near-infrared characteristic emission of LaOCl:Yb³⁺, Er³⁺ nanobelts was achieved under the excitation of a 532-nm laser. Commission Internationale de L'Eclairage analysis demonstrated that colour-tuned luminescence can be obtained by changing doping concentration of Yb³⁺ and Er³⁺, which could be applied in the fields of optical telecommunication and optoelectronic devices. The up-conversion luminescent mechanism and the formation mechanism of LaOCl:Yb³⁺, Er³⁺ nanobelts were also proposed.     

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.     

Synthesis and luminescence properties of Yb3+–Er3+ co-doped LaOCl nanostructures

LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Yb³⁺, Er³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameters of LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers, respectively, were 117.87 ± 15.48 and 141.09 ± 17.10 nm under the 95 % confidence level. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Yb³⁺, Er³⁺ nanostructures exhibited strong green and red UC emission centering at 526, 548, and 671 nm, respectively, attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_l5/2 transitions of Er³⁺ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the addition of Yb³⁺ ions, and the optimized molar ratio of Yb³⁺ to Er³⁺ was 10:1 in the as-prepared nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Yb³⁺, Er³⁺ nanostructures were achieved under the excitation of a 532-nm laser. CIE analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Yb³⁺ (and/or Er³⁺) ions and morphologies of nanomaterials, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism and the formation mechanisms of LaOCl:Yb³⁺, Er³⁺ nanofibers and hollow nanofibers were also proposed.     

Luminescence of GaS:Er<Superscript>3+</Superscript> and GaS:Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> layered crystals

Data are presented on the 300-K photoluminescence in GaS crystals doped with Er³⁺ or codoped with Er³⁺ and Yb³⁺. IR excitation (λ_ex = 976 nm) gives rise to anti-Stokes luminescence in GaS:Er³⁺ (0.1 at %) and GaS:Er³⁺,Yb³⁺ (0.1 + 0.1 at %) and leads to an increased intensity of the emission due to the ⁴ I _11/2 → ⁴ I _15/2 transitions. The anti-Stokes luminescence is shown to result from consecutive absorption of two photons by one Er³⁺ ion, and the increased intensity of Er³⁺ luminescence in GaS: Er³⁺,Yb³⁺ is due to energy transfer from Yb³⁺ to Er³⁺.     

Efficient up-conversion emission and energy transfer in LaAlO3 doped with Er3+, Ho3+, and Yb3+ ions

The spectroscopic properties of LaAlO₃ polycrystals doped with Er³⁺, Ho³⁺ and Yb³⁺ ions have been investigated. Very efficient up-conversion emission occurs upon IR excitation. The strongest luminescence has been observed for a sample doped with Er³⁺, Ho³⁺, and Yb³⁺ ions simultaneously and annealed at 1500 °C. An efficient energy transfer to Yb³⁺ ions is observed when Er³⁺ or Ho³⁺ ions are excited. The energy transfer mechanisms are proposed.     

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.     

Upconversion luminescence of Ho sensitized by Yb in transparent glass ceramic embedding BaYF5 nanocrystals

Transparent SiO₂-Al₂O₃-BaCO₃-YF₃-BaF₂ glass ceramics co-doped with Yb³⁺/Ho³⁺ ions were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy observation revealed that BaYF₅ nanocrystals incorporated with Yb³⁺ and Ho³⁺ were precipitated homogeneously among the oxide glass matrix. Three upconversion emission bands centered at 483 nm, 545 nm and 645 nm, corresponding to the ⁵F₃ → ⁵I₈, ⁵S₂, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively, were detected under 976 nm excitation, ascribing to the efficient energy transfer from Yb³⁺ to Ho³⁺. The red emission is prevailing in the precursor glass, while the green one turns to be dominant in the glass ceramic.     

Synthesis and two-color emission properties of BaGd2(MoO4)4:Eu3+,Er3+,Yb3+ phosphors

Eu³⁺, Er³⁺ and Yb³⁺ co-doped BaGd₂(MoO₄)₄ two-color emission phosphor was synthesized by the high temperature solid-state method. The structure of the sample was characterized by XRD, and its luminescence properties were investigated in detail. Under the excitation of 395 nm ultraviolet light, the BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ phosphor emitted an intense red light at 595 and 614 nm, which can be attributed to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺, respectively. The phosphor will also show bright green light under 980 nm infrared light excitation. The green emission peaks centred at 529 and 552 nm, were attributed to ⁴H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺, respectively. It indicated that the two-color emission can be achieved from the same BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ host system based on the different pumping source, 395 nm UV light and 980 nm infrared light, respectively. The obtained results showed that this kind of phosphor may be potential in the field of multi-color fluorescence imaging and anti-counterfeiting.     

Frequency upconversion properties of Er3+/Yb3+-codoped lead–germanium–bismuth oxide glasses

The frequency upconversion properties of Er³⁺/Yb³⁺-codoped heavy metal oxide lead–germanium–bismuth oxide glasses under 975 nm excitation are investigated. Intense green and red emission bands centered at 536, 556 and 672 nm, corresponding to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively, were simultaneously observed at room temperature. The influences of PbO on upconversion intensity for the green (536 and 556 nm) and red (672 nm) emissions were compared and discussed. The optimized rare earth doping ratio of Er³⁺ and Yb³⁺ is 1:5 for these glasses, which results in the stronger upconversion fluorescence intensities. The dependence of intensities of upconversion emission on excitation power and possible upconversion mechanisms were evaluated and analyzed. The structure of glass has been investigated by means of infrared (IR) spectral analysis. The results indicate that the Er³⁺/Yb³⁺-codoped heavy metal oxide lead–germanium–bismuth oxide glasses may be a potential materials for developing upconversion fiber optic devices.     

Synthesis and luminescence properties of Yb3+, Tm3+ and Ho3+ co-doped SrGd2(WO4)2(MoO4)2 nano-crystal

Novel up-conversion luminescent SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals were synthesized by hydrothermal method. The composition ratio of rare earth had been investigated. It indicated that when C_Yb³⁺ = 10 mol% and C_Yb³⁺/C_Tm³⁺/C_Ho³⁺ = 10:1.5:2, the emission intensities were the highest. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and up-conversion luminescence spectra were used to characterize SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals and they showed that the sample had high degree of crystallinity, the sample was tetragonal system, and the grain size of the sample was about 56 nm. Three emission peaks, including blue emission peak, green emission peak and red emission peak were observed at 477, 543 and 651 nm corresponding to ¹G₄ → ³H₆ and ¹G₄ → ³F₄ transitions of Tm³⁺, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively. All the emission peaks were observed by excitation of 980 nm semiconductor laser. The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process, green emission at 543 nm and red emission at 651 nm was a two-photon absorption process. The quantum yields of the sample were near 3.2%.     

Blue up-conversion emission of Yb3+-doped langbeinite salts

Yb³⁺-doped langbeinite salts were prepared by the solid solution method. X-ray diffraction patterns and vibrational spectroscopy confirmed that all obtained phases are highly pure, iso-structural and they crystallize in the cubic system with the space group P2₁3. The emission luminescence comes from the ²F_5/2 → ²F_7/2 transition of Yb³⁺ ions. Moreover, intense blue cooperative emission was observed at 476 nm under excitation in the near infrared at 975 nm.     

Intense 2.0 µm emission from Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Na<Subscript>5</Subscript>Lu<Subscript>9</Subscript>F<Subscript>32</Subscript> single crystal excited by 980 nm

This paper reported on optical spectra of Na₅Lu₉F₃₂ single crystals co-doped with ~?0.91 mol% Ho³⁺ and various Yb³⁺ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho³⁺/Yb³⁺ co-doped Na₅Lu₉F₃₂ and the energy transfer process from Yb³⁺ to Ho³⁺ ion. Compared with the Ho³⁺ singly doped Na₅Lu₉F₃₂ crystal, the Ho³⁺/Yb³⁺ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb³⁺ to Ho³⁺ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb³⁺ concentration when the concentration of Ho³⁺ ions is fixed at ~?0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23?×?10^?20 cm² according to the measured emission spectrum. The energy transfer efficiency from Yb³⁺:²F_5/2 to Ho³⁺:⁵I₆ for the crystal was estimated up to 90.8% indicating that Yb³⁺ ions can efficiently sensitize the Ho³⁺ ions.     

Upconversion photoluminescence in GeO2-PbO glass codoped with Nd3+ and Yb3+

Frequency upconversion (UC) photoluminescence (PL) in GeO₂-PbO glass codoped with trivalent ions of neodymium (Nd³⁺) and ytterbium (Yb³⁺) is reported. A diode laser operating at 977.7 nm, in resonance with the ytterbium transition ²F_7/2 → ²F_5/2, was the excitation source. Four PL spectral lines, corresponding to the Nd³⁺ transitions ⁴G_9/2 → ⁴I_9/2 (at 500 nm), ⁴G_7/2 → ⁴I_9/2 (at 550 nm), [⁴G_5/2; ²G_7/2] → ⁴I_11/2 (at 595 nm) and ⁴G_7/2 → ⁴I_13/2 (at 660 nm), were observed and characterized. The quadratic dependence of the PL intensities versus the laser power indicates that two laser photons participate in the UC process. The temperature dependence of the PL emissions from 300 to 390 K was also investigated to identify the contribution of phonons for the UC process. The dependence of the UC intensity with the Yb³⁺ concentration and the time behavior of the UC signal indicated the presence of two energy transfer (ET) pathways involving Nd³⁺-Yb³⁺ pairs and Yb³⁺-Nd³⁺-Yb³⁺ triads. Rate-equations for the population densities of the rare-earth energy levels were used to describe the dynamics of the UC emission and to determine the ET rates.     

Hydrothermal synthesis and infrared to visible up-conversion luminescence of Ho3+/Yb3+ co-doped Bi2WO6 nanoparticles

In this paper, Ho³⁺/Yb³⁺ co-doped Bi₂WO₆ (Ho³⁺/Yb³⁺-Bi₂WO₆) nanoparticles were successfully synthesized by a facile hydrothermal method followed by a heat treatment process. X-ray diffraction, field emission-scanning electron microscopy, energy dispersive spectroscopy and up-conversion luminescence spectra were used to characterize the as-synthesized Ho³⁺/Yb³⁺-Bi₂WO₆. The effects of Yb³⁺ concentration on up-conversion luminescence properties were investigated. Under 980?nm laser excitation, two emission peaks centered at 546?nm and 655?nm corresponding to the ⁵F₄, ⁵S₂ and ⁵F₅ transitions, respectively, to the ⁵I₈ ground state were observed. Power studies revealed that a two-photon process was involved in the up-conversion emissions and the probable up-conversion emission mechanisms were discussed according to the energy transfer process. This study confirms that Bi₂WO₆ could be a potential host to achieve desired up-conversion luminescence and might be potentially applied in the fields of photocatalysis and solar cells.     

NaScMo<Subscript>2</Subscript>O<Subscript>8</Subscript>:RE<Superscript>3+</Superscript> (RE = Tb,Eu, Tb/Eu,Yb/Er,Yb/Ho) phosphors: hydrothermal synthesis,energy transfer and multicolor tunable luminescence

NaScMo₂O₈:RE³⁺ (RE = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho) phosphors were successfully synthesized by surfactant-free hydrothermal method and post-calcination treatment. The energy transfer (ET) of MoO₄ ^2? → Tb³⁺ → Eu³⁺ was proved by photoluminescence spectra and decay features. Multicolor emissions (green → yellow → red) were obtained by adjusting the ratio of Tb³⁺/Eu³⁺ upon excitation into the MoO₄ ^2? at 292 nm. The ET of Tb³⁺ → Eu³⁺ was demonstrated to be a resonant type via a dipole–dipole mechanism, and the crystal distance (R _c) was calculated by the quenching concentration method. Under 980 nm excitation, the emission of NaScMo₂O₈:RE³⁺ (RE = Yb/Er, Yb/Ho) showed strong green (Yb³⁺/Er³⁺: ⁴S_3/2, ²H_11/2 → ⁴I_15/2; Yb³⁺/Ho³⁺: ⁵S₂ → ⁵I₈) luminescence, respectively. Moreover, the doping concentration of the Yb³⁺ has been optimized under a fixed concentration of Er³⁺ and Ho³⁺, respectively. The NaScMo₂O₈:RE³⁺ phosphors have potential applications for color displays and light-emitting devices due to a variety of luminous colors.     

A novel precursor route for Y2Mo4O15:Yb3+,Ho3+ phosphor and investigation of up-conversion luminescence

Hydrothermal reaction of Y(NO₃)₃·6H₂O and (NH₄)₆Mo₇O₂₄·4H₂O at 180 °C for 24 h was performed in this work via systematically varying the solution pH (4–10) and Mo/Y molar ratio (R, 2–5), which produced a NH₄Y(MoO₄)₂·0.19H₂O new compound that yielded phase-pure Y₂Mo₄O₁₅ upon calcination at 500–700 °C. The pH/R window for the compound to crystallize was determined to be 6–7/3 and 6–9/4–5. The products were characterized in detail by XRD, FTIR, elemental analysis, SEM, TEM, STEM and TG to understand chemical composition and the courses of phase/morphology evolution. Applying the above synthesis strategy successfully produced Y₂Mo₄O₁₅:xYb³⁺,yHo³⁺ phosphors that exhibit strong deep-red (630–670 nm, ⁵F₅ → ⁵I₈ transition) and weak green (530–560 nm, ⁵F₄/⁵S₂ → ⁵I₈) emissions under 978 nm laser pumping, where the optimal Yb³⁺ and Ho³⁺ contents were determined to be x = 0.20 for y = 0.01 and y = 0.03 for x = 0.10, respectively. Spectral analysis indicated that the up-conversion luminescence occurred via a two-photon process, with the red/green intensity ratio and also the emission color dependent on Yb³⁺ and Ho³⁺ contents, which were explained by considering ground state excitation, energy transfer, non-radiative relaxation and cross relaxation.     

The charge transfer excitation of trivalent rare earth ions Sm3+, Eu3+, Gd3+, Ho3+, Er3+ and Yb3+ emission in BaFC1 crystals

The charge transfer type excitation spectra of trivalent rare earth ions Sm³⁺, Eu³⁺, Gd³⁺, Ho³⁺, Er³⁺ and Yb³⁺ emission in BaFC1 crystals have been studied. The charge transfer type emissions of Ho³⁺, Er³⁺ and Yb³⁺ in BaFC1 have also been observed in addition to that of Eu³⁺. The energy of charge transfer band of these RE³⁺ ions were estimated experimentally and also calculated by Jørgensen's refined electron spin-pairing energy theory. Both the experimental and calculated values coincide well. The reductive enthalpy changes ΔH⁰_III−II of these RE ions were evaluated. Comparison of the variation of energy of the CT band maximum with that of the enthalpy change ΔH⁰_III−II shows a close agreement.     

Synthesis of Yb<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> co-doped β-NaYF<Subscript>4</Subscript> nanoparticles by sol–gel method and the multi-color upconversion luminescence properties

Well-crystalline β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles were synthesized by sol–gel method using isopropyl alcohol [(CH₃)₂CHOH] as a complexing agent. The samples were characterized by X-ray diffraction, scanning electron microscopic analysis and fluorescence spectrum analysis methods. Under the excitation of 980 nm laser diode (LD), the samples displayed bright upconversion luminescence (UCL), which was generated from the energy level transition of Ho³⁺ and Tm³⁺ ions. With the increase of Tm³⁺, Ho³⁺ and Yb³⁺-doping concentration, the UCL intensity of blue, green and red light emission of the samples varied. Calculation of the CIE color coordinate of the β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles revealed that with the adjustment of Tm³⁺, Ho³⁺ and Yb³⁺ doping concentration and the excitation power of 980 nm LD, the multi-color UCL can be realized. Approximately single red light output with the CIE color coordinate of x?=?0.545, y?=?0.306 and white light output with the CIE color coordinate of x?=?0.325, y?=?0.320 can be obtained in the synthesized β-NaYF₄: Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles.     

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.