Growth and Luminescent Properties of NaGd(WO4)2:Yb3+ Crystals

Data are presented on the spectroscopic properties of Yb³⁺-activated NaGd(WO₄)₂, a disordered scheelite-like tungstate potentially attractive as a gain medium. NaGd(WO₄)₂:Yb³⁺ crystals are grown by the Czochralski technique. The polarized absorption and luminescence spectra and the luminescence decay kinetics of oriented samples with different Yb³⁺ concentrations are studied at 300 K. The gain coefficients are calculated for different populations of the upper lasing level 2F _5/2 of the Yb³⁺ ion.     

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⁺).     

Spectroscopic properties of Yb3+-doped PbWO4 single crystal

Yb³⁺-doped PbWO₄ single crystal was grown using modified vertical Bridgman method. X-ray diffraction (XRD) analysis, optical absorption spectra, X-ray excited luminescence (XEL), fluorescence of ²F_5/2→²F_7/2 and its lifetime at room temperature were investigated. PWO:Yb³⁺ shows the broad absorption of Yb³⁺ (850–1050 nm) and efficient emission (950–1100 nm). Annealing exerts a distinct influence on the PWO:Yb³⁺ crystal, e.g. disappearance of color and annihilation of the absorption in the region around 450–750 nm, meanwhile the absorption of Yb³⁺ ions was enhanced by the annealing treatment. A novel luminescence band on the X-ray excited luminescence spectra of PWO:Yb³⁺ centered at about 500 nm was observed overlapped on that of PWO host.     

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⁺.     

Luminescent properties of Yb<Superscript>3+</Superscript>-doped hexagonal Ln<Subscript>3</Subscript>BWO<Subscript>9</Subscript> (Ln = Gd,Y)

We report the synthesis and spectroscopic characterization of polycrystalline Yb³⁺-doped (1, 2, and 5 at %) Ln₃BWO₉ (Ln = Gd and Y) borotungstates as candidate gain media for diode-pumped near-IR and visible solid-state lasers. Unpolarized luminescence and absorption spectra for the Yb^{3+ 2} F _7/2→² F _5/2 transition are measured at T = 77 and 300 K, the lifetime of the ² F _5/2 excited state is determined, and the emission cross section of the stimulated Yb^{3+ 2} F _5/2→² F _7/2 transition in these compounds is evaluated. Offering a combination of nonlinear optical and lasing properties, the Ln₃BWO₉ (Ln = Gd, Y) hexagonal borotung-states can be used as bifunctional media for diode-pumped lasers with nonlinear laser frequency self-conversion.     

Spectroscopy of Yb3+ in Cubic ZrO2 Crystals

The absorption and luminescence spectra of Yb³⁺ ions in yttria-stabilized zirconia crystals are studied. The site-selective luminescence spectra of a ZrO₂–12 mol % Y₂O₃–0.3 mol % Yb₂O₃ crystal are obtained under excitation at different wavelengths within the absorption band. For this crystal, Yb³⁺ luminescence spectra are also measured with 3-ms and 5-s delays relative to the excitation pulse. The results are interpreted under the assumption that the crystals contain three distinct types of optical centers.     

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.     

Near-infrared luminescence and energy transfer in CaMoO4: Ho3+, Yb3+ phosphor

Down-conversion (DC) is a promising avenue to break Shockley–Queisser detailed balance limit, and efficient DC from one ultraviolet visible photon to two near-infrared (NIR) photons is realized in the Ho³⁺ –Yb³⁺ co-doped CaMoO₄ system. The scheelite samples have been synthesized via solid-state reaction method. Upon blue light excitation (447 nm), Ho³⁺ transfers its energy to Yb³⁺ via resonant cross-relaxation process, bringing about NIR luminescence. The visible emissions decrease as a function of Yb³⁺ contents, while NIR emission at 996 nm first increases and then decreases due to CQ at Yb³⁺ contents beyond 15 mol %. The lifetime of Ho³⁺: ⁵F₄, ⁵S₂ → ⁵I₈ with various Yb³⁺ contents is calculated as 114, 85, 73, 70, 64, 59 and 55 μs, respectively. The maximum energy transfer efficiency and the corresponding DC quantum efficiency are estimated to be 48 and 148 %. The phosphor may be a potential candidate for application in enhancing the performance of crystalline silicon solar cells.     

Enhanced G4 emission in NaLaF4: Pr, Yb and charge transfer in NaLaF4: Ce, Yb studied by fourier transform luminescence spectroscopy

A high resolution luminescence study of NaLaF₄: 1%Pr³⁺, 5%Yb³⁺ and NaLaF₄: 1%Ce³⁺, 5%Yb³⁺ in the UV to NIR spectral range using a InGaAs detector and a fourier transform interferometer is reported. Although the Pr³⁺(³P₀ → ¹G₄), Yb³⁺(²F_7/2 → ²F_5/2) energy transfer step takes place, significant Pr³⁺¹G₄ emission around 993, 1330 and 1850 nm is observed. No experimental proof for the second energy transfer step in the down-conversion process between Pr³⁺ and Yb³⁺ can be given. In the case of NaLaF₄: Ce³⁺, Yb³⁺ it is concluded that the observed Yb³⁺ emission upon Ce³⁺ 5d excitation is the result of a charge transfer process instead of down-conversion.     

New,thermally stable Gd<Subscript>11</Subscript>(GeO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>O<Subscript>10</Subscript>-based upconversion phosphors

A series of Gd_11–x–y Yb _x Er _y GeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er^{3+ 2}H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B _en) in Gd_11–x–y Yb _x Er _y GeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B _en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.     

NIR-excited NIR and visible luminescent properties of amphipathic YVO<Subscript>4</Subscript>: Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> nanoparticles

This article reports the luminescence properties of amphipathic YVO₄:Er³⁺/Yb³⁺ nanoparticles (average grain size ca. 20 nm) obtained by an oleate-aided hydrothermal process. Depending on the upconversion (UPC) and downconversion (DWC) processes, they show luminescence in the visible and near-infrared (NIR) regions, respectively, by 980-nm excitation. The sample doped with Er³⁺:2.5 mol% and Yb³⁺:10 mol% showed the highest luminescence intensity in both the visible and NIR regions as a result of efficient energy transfer from Yb³⁺ to Er³⁺ ions. The hydrothermal treatment greatly enhanced both the DWC and UPC luminescence efficiencies. This is due to the reduction in the concentration of surface defects and ligands, accompanied by grain growth. NIR Fluorescence microscopy revealed for the first time that DWC luminescence is sufficiently intense for application of these nanocrystals as a NIR bioprobe.     

Fluoride and tellurite glasses for thin-film IR viewers

We have studied optical characteristics of Er³⁺-, Ho³⁺-, and Yb³⁺-doped ZBLAN and TWL glasses. Their luminescence was excited at wavelengths of 975, 378, and 449 nm. The 975-nm radiation excited the Yb³⁺ (² F _7/2 → ² F _5/2), and the excitation energy was then transferred to the Er³⁺ and Ho³⁺. The short-wavelength excitation led to cross-relaxation processes: (⁴ F _7/2, ² F _7/2) → (⁴ I _11/2, ² F _5/2) for the Er³⁺-Yb³⁺ pair (378 nm) and (⁵ F ₃, ² F _7/2) → (⁵ I ₅, ² F _5/2) for the Ho³⁺-Yb³⁺ (449 nm). At the three excitation wavelengths, we observed green luminescence in the range 525–550 nm. Using the glasses studied here, we prepared thin colorless lacquer films potentially attractive for hidden information recording and hidden labeling of various objects and materials.     

Visible to infrared energy conversion in Pr3+–Yb3+ co-doped fluoroindate glasses

Processes involving visible to infrared energy conversion are presented for Pr³⁺–Yb³⁺ co-doped fluoroindate glasses. The emission in the visible and infrared regions, the luminescence decay time of the Pr³⁺:³P₀ → ³H₄ (482 nm), Pr³⁺:¹D₂ → ³H₆ (800 nm), Yb³⁺:²F_5/2 → ²F_7/2 (1044 nm) transitions and the photoluminescence excitation spectra were measured in Pr³⁺ samples and in Pr³⁺–Yb³⁺ samples as a function of the Yb³⁺ concentration. In addition, energy transfer efficiencies were estimated from Pr³⁺:³P₀ and Pr³⁺:¹D₂ levels to Yb³⁺:²F_7/2 level. Down-Conversion (DC) emission is observed due to a combination of two different processes: 1-a one-step cross relaxation (Pr³⁺:³P₀ → ¹G₄; Yb³⁺:²F_7/2 → ²F_5/2) resulting in one photon emitted by Pr³⁺ (¹G₄ → ³H₅) and one photon emitted by Yb³⁺ (²F_7/2 → ²F_5/2); 2-a resonant two-step first order energy transfer, where the first part of energy is transferred to Yb³⁺ neighbor through cross relaxation (Pr³⁺:³P₀ → ¹G₄; Yb³⁺:²F_7/2 → ²F_5/2) followed by a second energy transfer step (Pr³⁺:¹G₄ → ³H₄; Yb³⁺:²F_7/2 → ²F_5/2). A third process leading to one IR photon emission to each visible photon absorbed involves cross relaxation energy transfer (Pr³⁺:¹D₂ → ³F₄; Yb³⁺:²F_7/2 → ²F_5/2).     

Yb<Superscript>3+</Superscript>-Activated inorganic aprotic liquids for diode-pumped lasers

This paper presents experimental data on the solubility of Yb(III) compounds in POCl₃–MCl _x , SOCl₂–MCl _x , and SO₂Cl₂–GaCl₃ binary aprotic solvents (where MClx is a Lewis acid). We have measured the absorption and luminescence spectra of Yb³⁺ in the solutions thus prepared. Liquid POCl₃–MCl₄–Yb³⁺ (M = Zr or Sn), SOCl₂–GaCl₃–Yb³⁺, and SO₂Cl₂–GaCl₃–Yb³⁺ gain media with [Yb³⁺] > 0.2 mol/L and an Yb³⁺ luminescence quantum yield η > 0.5 for diode-pumped lasers have been prepared for the first time.     

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.     

Yellow lighting upconversion from Yb3+/Ho3+ co-doped CaMoO4

Yellow upconversion (UC) luminescence is observed in Ho³⁺/Yb³⁺ co-doped CaMoO₄ synthesized by complex citrate-gel method. Under 980 nm excitation, Ho³⁺/Yb³⁺ co-doped CaMoO₄ exhibited yellow emission based on green emission near 543 nm generated by ⁴F₄, ⁵S₂ → ⁵I8 transition and strong red emission around 656 nm generated by ⁵F₅ → ⁵I₈ transition, which are assigned to the intra 4f transitions of Ho³⁺ ions. The optimum doping concentration of Ho³⁺ and Yb³⁺ was investigated for highest upconversion luminescence. Based on pump power dependence, upconversion mechanism of Ho³⁺/Yb³⁺ co-doped CaMoO₄ was studied in detail.     

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.     

The influence of Yb doping on the upconversion luminescence of Pr in aluminum oxide based powders prepared by combustion synthesis

The effect of ytterbium (Yb³⁺) doping on the upconversion (UC) emission of praseodymium (Pr³⁺) doped in aluminum oxide based powders prepared by combustion synthesis is reported for near-infrared excitation (λ = 980 nm). Our experimental results show that the crystalline structure and the UC emission changes with the Yb³⁺ concentration. The sample containing only Pr³⁺ (1.0 wt.%) did not show any UC signal and the UC emission profiles of the samples containing Pr³⁺ (1.0 wt.%) and Yb³⁺ (0.5, 2.0 wt.%) are quite different. The sample containing 0.5 wt.% of Yb³⁺ has five emission lines in the visible range associated to Pr³⁺ 4f–4f transitions, ³P₀ → ³H₄ (497 nm), ³P₀ → ³H₅ (525 and 550 nm), ³P₀ → ³H₆ (620 nm) and ³P₀ → ³F₂ (650 nm). We believe that the UC process has its origin in energy transfer from Yb³⁺ ions to Pr³⁺ ions in Pr_0.83Al_11.83O₁₉ phase. The sample containing 2.0 wt.% of Yb³⁺ has only one emission line in the visible range peaked at 507 nm which we believe has its origin in cooperative UC emission due to excited Yb³⁺ pairs in YbAlO₃ phase. The samples containing Yb³⁺ also present UC emission lines in the near-infrared which are assigned to intrinsic lattice defects.     

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.     

Upconversion Luminescence of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystals Doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> Ions

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd₂O₃) doped with Er³⁺ and Yb³⁺ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red (⁴F_9/2 → ⁴I_15/2 transition in Er3+ ion) and green (⁴S_3/2 → ⁴I_15/2 transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn²⁺ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.