Visible Upconversion Emission Research Articles

Luminescence properties of Y2WO6:Yb3+/Er3+ with enhanced red emission via upconversion

The Er3+/Yb3+ co-doped Y2WO6 phosphors were prepared via high temperature solid method for the first time. The structure was investigated with X-ray diffraction (XRD). The crystal morphology was observed through scanning electron microscopy (SEM). Under the excitation of 980 nm diode laser, visible up-conversion (UC) emissions were observed in green and red regions. The luminescence study reveals strong 4S3/2 to 4I15/2 transition at 545 nm and strong 4F9/2 to 4I15/2 transition at 657 nm. The relative intensities ratios of red (510–580 nm) to green (640–690 nm) emissions (RR/G) reduce when the samples co-doped with Yb3+ ions. The dependence of emission intensity on the pump power indicate that visible UC emissions are governed by two photons, meanwhile three photons process is also involved. For more details, the discussion is made in the energy level diagrams.

Tunability of green–red up-conversion emission of co-doped Ca3WO6:Yb3+/Er3+ powders

Color tuning of Ca3WO6:Er3+/Yb3+ phosphors were prepared via high temperature solid method in this paper. The structure was investigated with X-ray diffraction (XRD) and the crystal morphology was observed through scanning electron microscopy (SEM). Visible up-conversion (UC) emissions were observed in green and red regions under the excitation of 980 nm diode laser. The luminescence study reveals strong 4S3/2 to 4I15/2 transition at 550 nm and strong 4F9/2 to 4I15/2 transition at 661 nm, respectively. In addition, it also can be observed that the green band is quenched and the red emission enhanced as the Yb3+ concentration increases. In consequence, the CIE coordinates changed from (0.30, 0.65) in the green region to (0.61, 0.38) in the red region at different Er3+/Yb3+ concentration. Thus, the tuning properties of Ca3WO6:Er3+/Yb3+ phosphors suggest that they could be good candidates for applications in lighting.

Blue, green, red and near-infrared emissions via upconversion in α-sialon

Near-infrared to visible and near-infrared upconversion emission has been reported in Yb3+/Ln3+ (Ln3+=Er3+/Tm3+/Ho3+)-α-sialon ceramic prepared by hot press sintering technique. Under 980nm excitation, blue, green, red and near-infrared emissions are observed simultaneously as a result of the efficient energy transfer from Yb3+ to Er3+, Tm3+, and Ho3+ ions leading to a near-white light emission with CIE color coordinate of (0.38, 0.45). The two- and three-photon absorption processes are responsible for the observed upconversion emissions. The ceramic has moderately low phonon energy of 835cm−1. These novel properties make the material a promising candidate for upconversion applications.

RETRACTED: Near-infrared-to-visible upconverting luminescence of Er3+-doped CdSe nanocrystals grown by chemical bath

Abstract CdSe thin films were prepared by chemical bath and doped in situ with Er3+ ions. Three impurity levels were prepared by changing the relative volume of the salt solution containing Er3+ ions in the CdSe growing solution. Changes in the grain size (∼5.5–3.5 nm) and band gap energy (∼1.80–2.25 eV) were observed in the undoped and doped CdSe films, respectively. Photoluminescence studies displayed room temperature emission exhibiting NIR-to visible upconversion. The transition bands 4I13/2 → 4I15/2, 2I9/2 → 4I15/2 and 2F9/2 → 4F15/2 in the ∼700–850 nm region were investigated. Upconversion emissions were observed from the CdSeEr sample under light excitation (325 nm). The upconversion emission intensity ratio of these transitions is attributed to the variation of the local structure around Er3+ ions. These results confirm that visible upconversion emissions of Er3+ in the CdSeEr nanocrystals are mainly produced via two-photon excited-state absorption and energy transfer upconversion processes.

Enhanced luminescence properties of Nd3+ doped boro-tellurite glasses via silver additive

The improvement in the luminescence intensity of the rare earth doped glasses is a challenging issue. In this work, the effect of the silver nanoparticles on luminescence spectrum of Nd3+ doped boro-tellurite glasses is studied. The glasses are prepared by conventional melt-quenching technique and thermal processing to reduce the silver ions and nucleate metallic particles. The transmission electron microscopy is used to probe the formation and growth of the silver nanoparticles with an average size of about 18nm after 12h of continuous heat-treatments. The visible upconversion emissions are enhanced up to 3 times after 4h of heat-treatment, applying an excitation wavelength at 800nm. A 2.3-fold enhancement is also observed in near-infrared emission (centered at 1.06μm). The mechanisms and interactions between metal species and rare earth ions are discussed.

Enhanced green upconversion emission in Ho3+:Gd2O3 phosphor by codoping of Yb3+ ions

The present study explores the enhanced visible frequency upconversion emissions in the Ho3+-Yb3+ codoped Gd2O3 phosphors prepared by combustion technique. The green colour emission capability with relatively low red and NIR emissions has been confirmed under 980 nm continuous wave (CW) laser diode excitation. Three upconversion emission transitions (5F4, 5S2 →5I8, 5F5→ 5I8 and 5F4, 5S2 →5I7) has been confirmed due to presence of Ho3+ ions in Gd2O3 phosphors. By further codoping of Yb3+ ions in Ho3+:Gd2O3 phosphor, an improved upconversion emission has been reported due to the energy transfer between Yb3+ to Ho3+ ions. The observed results support that the prepared codoped phosphor can produce overall green colour emission and may be used in making green display devices and upconverters.

Visible and near-infrared upconversion in α-sialon ceramics

Intense near-infrared to visible and near-infrared upconversion emissions are realized in Er3+/Ho3+/Tm3+ doped α-sialon ceramics.

Near-Infrared to Visible Upconversion Emission Induced Photopolymerization: Polystyrene Shell Coated NaYF<sub>4</sub> Nanoparticles for Fluorescence Bioimaging and Nanothermometry

Near-Infrared to Visible Upconversion Emission Induced Photopolymerization: Polystyrene Shell Coated NaYF<sub>4</sub> Nanoparticles for Fluorescence Bioimaging and Nanothermometry

Enhanced 1.8 μm emission in Er3+/Tm3+ co-doped lead silicate glasses under different excitations for near infrared laser

A detailed study of the fluorescence emission properties and energy transfer mechanism in Er3+/Tm3+ co-doped lead silicate glasses was reported. Enhanced near infrared 1.8 μm and visible up-conversion emissions were investigated under 808 and 980 nm excitations, respectively. The energy transfer mechanism between Er3+ and Tm3+ was analyzed according to the absorption spectra, the emission spectra and the level structures of Er3+ and Tm3+. The energy transfer efficiency between Er3+ and Tm3+ reached 68.1% in the Er3+/Tm3+ co-doped lead silicate glasses when pumped by 808 nm laser diode. Based on the absorption spectra, the Judd-Ofelt parameters, spontaneous emission probability, absorption and emission cross sections, gain coefficients were calculated and analyzed. It was found that the calculated emission cross section and the maximum gain coefficient around 1.8 μm were 4.9×10−21 cm2 and 1.12 cm−1, respectively. These results indicated that the Er3+/Tm3+ co-doped lead-silicate glasses had potential application in near infrared lasers.

Structure refinement and up-conversion of Ho3 +/Er3 + Co-doped 12CaO·7Al2O3

Crystal structures, thermodynamics characters and optical properties of pure 12CaO·7Al2O3 (C12A7) and Ho3+/Er3+ co-doped C12A7 (C12A7-Ho3+/Er3+) derivatives have been studied using XRD, DSC/TG and Raman spectra analysis, respectively. Testing samples were sintered at 1173K from compacted precursor powders after co-precipitation. Effect of pH change on grain size of C12A7 was estimated via Scherrer's Equation. Activation energy of crystal growth for C12A7 polycrystals was measured according to Kissinger/Ozawa methods to be 238/258kJ·mol−1 respectively. Lattice constant (a) and Reference Intensity Ratio (RIR) of pure C12A7 were evaluated to be a=12.0122(2) Å and RIR=0.79 (5%). Fluorescence effects of Raman spectra around 1200–1400 and 2000–2500cm−1 and pure visible up-conversion emission of 520–540nm were observed from C12A7-Ho3+/Er3+ powders under 488nm laser diode and 793nm Xe lamp excitation, respectively. Three relaxations and cooperative transformation mechanisms of Ho3+/Er3+ ions were proposed to explain up-conversion of pure green light process.

Spectroscopic investigation of zinc tellurite glasses doped with Yb3 + and Er3 + ions

This paper presents a detailed spectroscopic investigation of zinc tellurite glasses with the compositions (0.80−x−y) TeO2+(0.20) ZnO+xEr2O3+yYb2O3 (x=0, y=0; x=0.004, y=0; x=0, y=0.05 and x=0.004, y=0.05 per moles). The samples were synthesized by the conventional melt quenching method. The optical absorption and emission measurements were conducted at room temperature to determine the spectral properties of lanthanides doped zinc tellurite glasses and, to study the energy transfer processes between dopant lanthanide ions. The band gap energies for both direct and indirect possible transitions and the Urbach energies were measured from the absorption spectra. The absorption spectra of the samples were analyzed by using the Judd-Ofelt approach. The effect of the ytterbium ions on the emission properties of erbium ions was investigated and the energy transfer processes between dopant ions were studied by measuring the up-conversion emission properties of the materials. The color quality parameters of obtained visible up-conversion emission were also determined as well as possibility of using the Er3+ glasses as erbium doped fiber amplifiers at 1.55μm in infrared emission region.

Visible up-conversion and near-infrared luminescence of Er3+/Yb3+ co-doped SbPO4-GeO2 glasses

Recent advances in glass chemistry have led to new multifunctional optical glasses of great technological importance. Glasses containing high amounts of antimony have been studied for use in nonlinear optics, near-infrared transmission, and as hosts for rare-earth ions in photonic devices. This work describes a luminescence study of Er3+ and Er3+/Yb3+ co-doping in a new SbPO4-GeO2 binary glass system. Near-infrared and visible up-conversion emissions were observed in the green and red regions, which are enhanced when the samples are co-doped with Yb3+. Near-infrared emissions have good quantum efficiency and full width half maximum of 61 nm. Visible up-conversion emissions are governed by two photons and described by excited state absorption, energy transfer and cross-relaxation processes.

Synthesis and Characteristic of the NaYF4/Fe3O4@SiO2@Tb(DBM)3 · 2H2O/SiO2 Luminomagnetic Microspheres with Core–Shell Structure

The structure and properties of the multifunctional nanoparticles were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Photoluminescence spectra and Vibrating sample magnetometer (VSM). The experimental results show that the microsphere has the magnetic core and silica shell bonded with terbium complex. These multifunctional nanoparticles exhibit strong visible emission and up-conversion emission, which is based on the use of up-converting nanoparticles (UCNPs) of the NaYF4:Yb3+, Er3+/Tm3+ type that can be excited with 980 nm laser light to give a green and red luminescence, moreover, nanoparticles possess magnetism with a saturation magnetization of 18.48 emu/g and paramagnetism at room temperature.

Improved Near-Infrared Up-Conversion Emission of Tm3+ Sensitized by Yb3+ and Ho3+ in LuF3 Nanocrystals.

In the present work, mono-disperse and uniform orthorhombic lutetium fluoride (LuF3) nanocrystals with an average size of about 35 nm have been successfully synthesized by a simple ionothermal method without any template. The infrared (IR) to visible up-conversion (UC) photoluminescence of LuF3 doped with Yb3+, Tm3+, and Ho3+ under 980 nm excitation was systemically studied. The intensity of near infrared (NIR) to visible up-conversion emission of Tm3+ was improved efficiently by adding Yb3+ and Ho3+ in LuF3, especially for the broad NIR emission band located at 812 nm. Meanwhile, compared to the Yb3+ and Tm3+ co-doped LuF3, the ratio of red to green emission in the Yb3+, TmS+, and HoS+ co-doped LuF3 changed greatly, and a bright yellowish-green emission was observed under 980 nm laser excitation. It shows that Yb3+, Tm3+ and Ho3+ co-doped LuF3 nanocrystals provided a potential application in vitro and in vivo bio-imaging, color displays and optical storage.

Effect of Ce3+ Concentration on the Luminescence Properties of Ce3+/Er3+Nb3+ Tri-Doped NaYF4 Nanocrystals.

In order to investigate the effect of Ce3+ concentration on the emission properties of ErS+/y3+ codoped NaYF4 nanocrystals, Ce3+/Er3+/Yb3+ tri-doped NaYF4 nanocrystals were prepared through a facile EDTA-assisted hydrothermal method. The upconversion .(UC) and the near infrared (NIR) emission properties of Er3+ ions were systematically investigated in the NaYF4:Ce3+/Er3+/Yb3+ nanocrystals. Under 980 nm excitation, with the increasing of Ce3+ concentration, the emission intensity of Er3+ at 1550 nm (4I13/2 --> 4I15/2) band increases initially and then decreases. The increase of the fluorescence intensity of 1550 nm is due to the energy transfer between Er+ and Ce3+ ions: Er3+:4(11/2)+Ce3+:2F5/2 --> Er3+:4I13/2 +Ce3+:2F7/2. But when Ce3+ doping concentration is 2.0%, the cross relaxation:Er3+:4I13/2+ Ce3+:2F5/2 --> Er3+:4I15/2+Ce3+:2F7/2 happens, which depopulates the 4113/2 level of Er3+ and results in the decrease of the emission intensity of Er3+ at 1550 nm band. Meanwhile, incorporation of Ce3+ dramatically decreases the visible UC emission intensity. A possible emission mechanism was proposed.

Broadband Near-Infrared Photoluminescence and Strong Visible Up-Conversion Emission in BaTiO3-(Na0.5Er0.5)TiO3 Lead-Free Piezoelectric Ceramics

For checking photoluminescence properties of BaTiO3-(Na0.5Er0.5)TiO3 lead-free piezoelectric ceramics, optical diffuse reflection spectra, visible up-conversion luminescence spectra, 1.55 μm near-infrared photoluminescence spectra, and optical temperature sensing performances under the excitation of 980 nm laser were investigated systematically. Broadband near-infrared (˜1.55 μm, FWHM˜90 nm) emission and strong visible up-conversion (˜550 nm) emission were observed under the 980 nm excitation in the ceramics at room temperature. Near-infrared emission and visible up-conversion emission became stronger with increasing (Na0.5Er0.5)TiO3 concentration below quenching point above which it will degrade. The optimal emission intensity was obtained when (Na0.5Er0.5)TiO3 content was 7 mol%. These ceramics with excellent ferro-/piezoelectric and photoluminescence properties may be useful for ultrasonic transducer, optical temperature sensor, optical amplifier, and other relative applications.

Emission in Gd6O5F8:Yb3+,Er3+ micro-particles for multimodal luminescence and temperature sensing upon 980 nm excitation.

Mono-dispersed Gd6O5F8:Yb3+/Er3+ micro-particles with different doping concentrations (Er3+: 0.1-1%) were synthesized by a facile hydrothermal route. The emission spectra, luminescent dynamic power-dependence and temperature sensing of up-conversion photoluminescence were investigated in detail. Under 980 nm excitation, the as-prepared samples exhibit intense red up-conversion and NIR emissions, which are influenced by the doping concentrations of Er3+ within Gd6O5F8. With increasing concentrations of Er3+ ions, the visible up-conversion emissions first increase and then decrease, but NIR down-conversion emissions display a distinct trend, in which one peak at 1010 nm is highly suppressed and another at 1530 nm is increased quickly. Furthermore, the 980 nm excited optical temperature sensing property of the synthesized sample is realized over a wide temperature range by monitoring the intensity of up-conversion luminescence. The study provides a novel strategy based on lanthanide oxy-fluoride micro-particles for multifunctional displays, lighting and temperature sensing in a single system.

Er3+-Tm3+-Yb3+:Gd2O3 upconverting phosphors for sensing and laser induced heating applications

This paper explores the near infrared (NIR) to visible frequency upconversion emissions in the Er3+−Tm3+−Yb3+ tri-doped Gd2O3 phosphors prepared by the combustion technique. The cubic phase formation and crystalline structure of the prepared materials has been examined with the help of X-ray diffraction study. The multicolour upconversion emission capability of the prepared materials has been confirmed under the excitation with 980-nm NIR laser source. The relative intensity variation corresponding to the transitions from the thermally coupled energy levels ( $^{2}\text{H}_{11/2}$ , $^{4}\text{S}_{3/2}$ ) to the ground level ( $^{4}\text{I}_{15/2}$ ) of Er3+ ions with pump power and temperature has been studied to investigate the optical temperature sensing ability of the prepared material. The maximum sensor sensitivity of the synthesized material reaches the value 0.0073 $\text{K}^{-1}$ at 443 K. The laser-induced heating capacity of the prepared material caused by laser excitation at different pump powers has been analyzed. The observed results support the utility of the prepared materials in optical temperature sensing and laser-induced heating along with additional capability for being used in making NIR to visible upconverter.

Unraveling Morphology and Phase Control of NaLnF4 Upconverting Nanocrystals

Near-infrared to visible upconversion NaLnF4 (Ln = Pr to Lu and Y) nanocrystals hold great promise for use in biological labeling and imaging due to their intrinsic characteristics such as high chemical stability, nonblinking and sharp bandwidth luminescence, large Stokes shift, as well as appropriate and abundant energy states necessary for efficient energy transfer to achieve near-infrared to visible upconversion emission. However, there are still significant hurdles in the control of size, shape, and phase of NaLnF4 nanocrystals due to limited understanding of their growth behavior and growth mechanism. Here we describe an approach to facilely control the shape and phase of upconversion NaLnF4 nanocrystals. Besides the optimization of synthetic conditions such as organic surfactant and reaction temperature, we have developed a program, in which a correlation between the ionic radius of lanthanide ions and the shape/phase of NaLnF4 nanocrystals is established, to precisely control the shape and phase of...

Broadband 27 μm amplified spontaneous emission of Er^3+ doped tellurite fibers for mid-infrared laser applications

Er3+ doped tellurite fibers have been fabricated using a convenient suction technique. Different scanning calorimetry (DSC), Electro-probe micro-analyzer (EPMA), Raman, steady and dynamic luminescence spectra were performed to investigate their thermal, structure, and luminescent properties. Broadband 2.7 μm amplified spontaneous emission (ASE) emission with concurrent 1.5 μm and visible up-conversion emissions have been achieved in fibers with various lengths upon the excitation of 980 nm laser diode (LD). A quantitative study of the spectroscopic properties has been further analyzed in detail according to the Jude-Ofelt model, rate equation, and Dexter’s theory to evaluate the competitive relationship among them. The desirable spectroscopic characteristics associated with excellent thermal stability and mechanical properties indicate that the Er3+ doped tellurite fibers are excellent host matrices for 2.7 μm lasing and may provide applications in mid-infrared fiber lasers and amplifiers.