White Upconversion Research Articles

White upconversion emission in Er3+/Yb3+/Tm3+ codoped LiTaO3 polycrystals

White upconversion emission was observed in Er3+/Yb3+/Tm3+:LiTaO3 polycrystals prepared by solid-state reaction method. The structural properties of Er3+/Yb3+/Tm3+:LiTaO3 polycrystals were confirmed by X-ray diffraction (XRD) patterns. The color coordinate of (0.33, 0.33) in 1mol% Er3+/20mol% Yb3+/1mol% Tm3+:LiTaO3 polycrystal was found to be equal to the standard point of energy white-light. The blue emission was populated via the cooperative sensitization upconversion process, and efficient two-photon green upconversion and one-photon red upconversion emissions were observed. The increased green upconversion emission was attributed to the fast cross relaxation process of 3H4 (Tm)+4I13/2 (Er)→3H6 (Tm)+4S3/2 (Er). The gained excellent optical quality of white upconversion emission suggested that Er3+/Yb3+/Tm3+:LiTaO3 polycrystal will be a potential laser candidate material for the application of the three-dimensional backlighting.

Fabrication and markedly enhanced white up-conversion emission of core–shell structured NaGdF4:Tm3+/Yb3+/Ho3+@SiO2

Core–shell structured NaGdF4:Yb3+/Tm3+/Ho3+@SiO2 microrods were successfully prepared via the Stober sol–gel method by coating a layer of silica on the surface of NaGdF4:Yb3+/Tm3+/Ho3+ particles derived from a hydrothermal process. The phase, structure, morphology and up-conversion (UC) luminescence properties were characterized by various techniques. It is found that the products with core–shell structure exhibit bright UC emissions. Strong white light emission is generated by tuning the Tm/Ho molar ratio in the Tm/Ho co-doped system. The formation process of the core–shell sample has also been discussed. In particular, the white UC emission can be markedly enhanced by coating a silica layer onto the surface of the phosphors, showing great potential in display and lighting fields.

White up-conversion luminescence of NaYF4:Yb3+,Pr3+,Er3+

Photon up-conversion which yields higher energy emission by stacking lower energy photons is possible only with specific rare earth ions. Despite this, it has several potential applications. NaYF4 with Yb3+,Er3+ co-doping has been recognized as one of the most feasible materials for efficient up-conversion luminescence. In this work, the up-conversion luminescence of the Pr3+–Er3+ combination was studied using sensitization by Yb3+. Emission was observed in the visible including blue, green, yellow, orange and red. These are due to the 3P0,1→3H4–6,3F2–4 and 1D2→3H4 (Pr3+) as well as 2H11/2,4S3/2,4F9/2→4I15/2 (Er3+) transitions. Concentration quenching of the Pr3+ luminescence was observed already with 1mol-% due to many cross-relaxation processes. With naked eye, the up-conversion luminescence was seen as white light. The CIE chromaticity coordinates are close to those of the standard illuminant F4 which represents warm white.

White upconversion photoluminescence for Er3+–Tm3+–Yb3+ tri-codoped bismuth titanate ferroelectric thin films

The upconversion (UC) photoluminescence and ferroelectric properties of Er3+–Tm3+–Yb3+ tri-codoped bismuth titanate (BETYT) thin films were studied. The thin films were prepared by chemical solution deposition method. There are four emission bands in the visible UC luminescence spectra excited by 980nm at room temperature. The 478nm blue emission band corresponds to 1G4→3H6 transition of Tm3+, and the 527nm, 548nm green emission bands correspond to 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+, and the 657nm red emission band corresponds to 4F9/2→4I15/2 transition of Er3+ and 1G4→3F4 transition of Tm3+. The fluorescent color can be tuned by adjusting Er3+, Tm3+ and Yb3+ concentrations and the optimal color coordinate in these films is (0.31, 0.34), very close to the standard white-light coordinate of (0.33, 0.33) when pumped under power intensity about 2.8W/cm2. The UC emission mechanism was discussed and there exist significant energy transfers from Er3+ to Tm3+, which will affect the relative intensity of blue, green and red emissions and their quenching concentrations. The remanent polarization (2Pr) value of BEr0.0085TYT thin film prepared on Pt/Ti/SiO2/Si substrate is 27.8μC/cm2. The combination of UC photoluminescence and ferroelectric properties in BETYT thin films would open the possibility of inventing novel multifunctional optoelectronic integration devices.

Super-intense white upconversion emission of Yb_2O_3 polycrystals and its application on luminescence converter of dye-sensitized solar cells

In this Letter, we present the observation of super-intense upconversion (UC) white emission of Yb2O3 under 980 nm excitation, its evolution on excitation power density, the UC mechanism, and its application on the luminescence converter of dye-sensitized solar cells (DSSCs). It is significant to observe that Yb2O3 demonstrates at least one order more intense UC luminescence than β-phase NaYF4:Yb3+, Er3+ and Yb2O3/DSSCs exhibit much better photovoltaic performance than β-phase NaYF4:Yb3+, Er3+/DSSCs under strong excitation. This indicates that Yb2O3 would become a novel candidate of the solar energy converter, especially in the application of concentrator solar cells.

Bright white upconversion luminescence in Ho3+/Yb3+/Tm3+ triple doped CaWO4 polycrystals

Abstract Ho 3+ /Yb 3+ /Tm 3+ triple doped CaWO 4 polycrystals are synthesized by a sample high temperature solid state method. The crystal structure of the polycrystals is characterized by means of X-ray diffraction.Under single-wavelength diode laser excitation of 980 nm, the bright white light consists of the blue, green, and red upconversion radiations which correspond to the transitions 1 G 4 → 3 H 6 of Tm 3+ ions, 5 S 2 / 5 F 4 → 5 I 8 and 5 F 5 → 5 I 8 of Ho 3+ ions, respectively. The pump power plays an important role in the blue upconversion emission intensity, and it helps to the adjustment of the white upconversion emission chrominance. The calculated color coordinates display that white light can be achieved by adjusting pump powers. The CIE coordinate close to (0.33, 0.33) is potentially suitable for the widely realistic application in the field of displays, lasers, and lighting technology. The possible upconversion mechanisms are investigated and discussed.

Controllable and white upconversion luminescence in LiNbO3:Ln3+ (Ln = Ho, Yb, Tm) single crystals

Ho3+, Yb3+ and Tm3+ tri-doped LiNbO3 single crystals with various dopant concentrations were prepared by Czochralski method. Controllable and white upconversion emissions are generated under 980nm excitation at room temperature. The variations of upconversion spectra and CIE coordinates with dopant concentrations and pump powers are studied in details on the basis of energy transfer processes. Ideal white-light emissions can be obtained even though the pump power is varied from 100 to 900mW. Based on the present experiments, great inspirations are given in realizing the target color of interest by varying dopant concentrations and pump powers.

Tunable white upconversion luminescence in Ho3+/Tm3+ co-doped Yb-based LiYb(MoO4)2

The Ho3+/Tm3+ co-doped LiYb(MoO4)2 phosphors were synthesized by solid state reaction. The crystal phase was characterized by the X-ray powder diffraction. The blue emission of Tm3+ at 475nm and the green and red emissions of Ho3+at 545 and 660nm, respectively, are observed under the laser excitation at 975nm. The tunable white upconversion luminescence is realized by varying Ho3+ and Tm3+ concentrations in LiYb(MoO4)2. Bright white upconversion emission is observed in 0.2%Ho3+/0.8%Tm3+ co-doped LiYb(MoO4)2. Based on laser pump power, upconversion emission mechanism and population process are discussed in detail.

Bright white up-conversion emission from Er3+/Ho3+/Tm3+/Yb3+ co-doped YVO4 phosphors

Er3+/Ho3+/Yb3+/Tm3+ co-doped YVO4 phosphors were synthesized by the conventional solid-state reaction. Under 980nm laser diode excitation, intense red, green and blue up-conversion emissions were observed for the Yb3+/Er3+, Yb3+/Ho3+ and Yb3+/Tm3+ couples in the YVO4 host, respectively, which were due to the successive energy transfer from Yb3+ to Er3+, Ho3+ or Tm3+. Bright white luminescence upon 980nm near-infrared excitation can be observed for the sample at the optimum chemical composition of YVO4:10%Yb3+/1%Tm3+/0.3%Ho3+/0.2%Er3+. Under different excitation pump powers, the obtained optimal color coordinate (0.323, 0.325) is very close to the standard white light (0.333, 0.333) coordinate.

White upconversion emission in Li+/Yb3+/Tm3+/Er3+-doped Gd6MoO12 phosphors

The Yb3+/Er3+/Tm3+-doped Gd6MoO12 phosphors and Li+/Yb3+/Er3+/Tm3+-doped Gd6MoO12 phosphors were synthesized by the high-temperature solid-state method. Under 980nm laser diode excitation, the Gd6MoO12:Li+/Yb3+/Er3+/Tm3+ phosphors show the white upconversion (UC) emission at the pump power of 200mW/cm2, which is composed of the blue (1G4→3H6 of Tm3+), green (2H11/2, 4S3/2→4I15/2 of Er3+), and red (4F9/2→4I15/2 of Er3+) UC emissions. The calculated CIE color coordinates of Gd6MoO12:Tm3+/Er3+/Yb3+ phosphors changed from blue area to white area after the Li+ ion doping. Then, the effect of Li+ ions mixing on the emission was analysed. The relative UC mechanisms and properties were also investigated and proposed based on their spectral. The additional mixed Li+ ions enhanced the red and green upconversion emission largely in this phosphor and then formed the white UC emission, which indicated that the Li+ is a promising dopant for tuning white light luminescence in some case.

Color control and white upconversion luminescence of LaOF:Ln3+ (Ln = Yb, Er, Tm) nanocrystals prepared by the sol–gel Pechini method

A series of Yb(3+)-Er(3+) and Yb(3+)-Er(3+)-Tm(3+) codoped LaOF nanocrystals were synthesized via a modified sol-gel Pechini method. The phases and morphologies as well as the luminescence properties of the as-prepared samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and upconversion luminescence (UCL) spectra, respectively. Under 980 nm near infrared (NIR) excitation, the UCL properties and the corresponding luminescent colors of the samples could be precisely modulated by changing the annealing temperatures, the dopant concentrations and the pump densities. By regulating the intensities of blue, green and red emissions in Yb(3+)-Er(3+)-Tm(3+) codoped LaOF nanocrystals, an ideal white upconversion luminescence with chromaticity coordinates of (0.331, 0.368) is obtained in La0.885Yb0.1Er0.01Tm0.005OF nanocrystals for the first time. The blue, green and red components of the white light come from the (1)G4 → (3)H6 transition of Tm(3+), (2)H11/2/(4)S3/2 → (4)I15/2 transitions of Er(3+) and (4)F9/2 → (4)I15/2 transition of the Er(3+) ions, respectively. The possible physical mechanisms involved in the different upconversion processes were discussed in detail.

Hollow structured SrMoO4:Yb3+, Ln3+ (Ln = Tm, Ho, Tm/Ho) microspheres: tunable up-conversion emissions and application as drug carriers.

In this study, a facile and mild one-pot approach was employed to prepare hollow-structured SrMoO4 spheres using soluble sodium poly(4-styrenesulfonate) (PSS) as a soft template. It is found that the as-prepared product exhibits hollow spherical morphology, good dispersity, and narrow size distribution. The formation mechanism has also been proposed. Tunable multicolor and bright white up-conversion (UC) emissions were successfully realized by precisely adjusting the doping sensitizer (Yb3+) and activator (Tm3+, Ho3+, and Tm3+/Ho3+) concentration in the host matrix. MTT assay shows the good biocompatibility of SrMoO4:Yb3+/Tm3+ hollow spheres, which were used as an anti-cancer drug carrier to evaluate the loading and controlled release behavior by selecting doxorubicin hydrochloride (DOX) as a model drug. Drug release tests reveal a sustained drug release behavior and especially the UC emission intensities of the drug loaded system increase with the released amount of DOX, indicating that the extent of drug release can be monitored or tracked by the change in emission intensity. Moreover, the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carrier was investigated and the endocytosis process of drug-loaded microspheres was studied using confocal laser scanning microscopy (CLSM) and flow cytometry. Considering the good biocompatibility, high drug loading amount and obvious sustained drug release properties, the hollow microspheres are highly promising in biological areas.

Multicolor and bright white upconversion luminescence from rice-shaped lanthanide doped BiPO4 submicron particles

In this paper, uniform rice-shaped lanthanide doped BiPO4 upconversion submicron particles have been successfully synthesized via a facile room-temperature co-precipitation reaction and subsequent calcination route. The morphology, phase transformation and upconversion luminescent properties of synthesized submicron particles (SMPs) were characterized by using different analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC) and upconversion luminescence (UCL) spectra. The transformation from hexagonal phase to monoclinic phase is crucial for upconversion luminescent properties due to the loss of water molecules in the lattice of hexagonal phase. With different variety and concentration of the dopant Ln(3+) (Ln = Yb, Er, Tm and Ho) ions, the obtained samples present bright green, blue, and red upconversion emissions under a 980 nm continual wave laser diode excitation. Multicolor and bright white upconversion emissions have also been obtained by precisely adjusting the dopants concentration in the host lattice.

Enhanced upconversion multicolor and white light luminescence in SiO2-coated lanthanide-doped GdVO4 hydrothermal nanocrystals

Tetragonal zircon-type codoped Yb, Ln–GdVO4 (Ln=Tm, Ho, Er) upconverting nanocrystals with square and rectangular sections were prepared through an efficient low-temperature hydrothermal synthesis. Further processing that combined annealing at 600 °C followed by coating of the surface with a uniform 5 nm-shell of SiO2 resulted in a significant improvement of the intensity of the upconverted emitted visible light following near-infrared (∼980 nm) diode laser excitation with respect to raw hydrothermal nanocrystals. Strong tunable color and bright visible light composed of red–green, blue and green emissions from Ho3+, Tm3+ and Er3+, respectively, were generated by adjusting the Yb–Ln composition of these silica-coated nanocrystals. Based on calculations of CIE color coordinates, nearly ideal white upconversion light was achieved for samples of composition Gd0.829Yb0.15Tm0.01Ho0.009Er0.002VO4.

White upconversion luminescence in Tm3+/Ho3+/Yb3+ triply doped K+–Na+ ion-exchanged aluminum germanate glass channel waveguide

Rare-earth ions doped K+–Na+ ion-exchanged aluminum germanate (NMAG) glass channel waveguides have been designed and fabricated. Under 980nm laser pumping, an intense upconversion white light transmission trace was observed in Tm3+/Ho3+/Yb3+ triply doped NMAG glass channel waveguide and a high-brightness light spot was achieved from the output end of the fiber connected to the waveguide channel. The fluorescent colors were diverse and located within or near the white region in CIE chromaticity diagram under various pumping powers. These admirable results indicate that Tm3+/Ho3+/Yb3+ triply doped NMAG channel waveguide is a promising light source for medical and high-precision processing illumination.

White upconversion emission in Yb3+/Tm3+/Ho3+ doped SrMoO4 nanocrystals by high excited state energy transfer

The SrMoO4:Yb3+/Tm3+/Ho3+ nanocrystals have been successfully synthesized via a sol–gel process. Under 976nm laser diode excitation, the nanocrystals show the intense white upconversion (UC) emission, which is composed of the blue (1G4→3H6 of Tm3+), green (5F4/5S2→5I8 of Ho3+), and red (5F5→5I8 of Ho3+) UC emissions. The UC mechanisms based on spectral, kinetic, and pump power dependence analyses were discussed. It indicates that the white UC emission is attributed to the high excited state energy transfer from the sensitizer Yb3+−MoO42− dimer to the activators (Tm3+ and Ho3+), which can partly decrease the non-radiative processes at the lower energy levels of the activators.

WHITE UPCONVERSION LUMINESCENCE FROM (Yb3+/Tm3+/Ho3+) TRIDOPED GdF3 NANORODS AFTER HEAT TREATMENT

A series of Ho3+/Yb3+/Tm3+ tridoped GdF 3 nanorods with different dopant concentrations were synthesized by a hydrothermal method. Transmission electron microscope (TEM) images indicate that the length and diameter of the nanorods is about 90 nm and 31 nm, respectively on average. No bright white upconversion light was observed from the samples with different Yb 3+, Ho 3+ or Tm 3+ concentrations. Unexpectedly, the emission color coordinates of the samples after heat treatment move toward the central white region of the chromaticity diagram, and among these samples, the color coordinate (0.349, 0.329) of GdF 3:15% Yb 3+, 0.1% Ho 3+, 0.8% Tm 3+ is the most close to the standard white light (0.333, 0.333). This is unlike previous reports in which white light was achieved via tuning dopant concentration or excitation power. The reasons for the above phenomenon are presented by means of FT-IR spectra and the energy level diagram of dopants.

Tunable multicolor and bright white emission of one-dimensional NaLuF4:Yb3+,Ln3+ (Ln = Er, Tm, Ho, Er/Tm, Tm/Ho) microstructures

Well-defined one-dimensional NaLuF4:Yb3+,Er3+/Tm3+/Ho3+ microtubes and microrods were successfully prepared by a surfactant-free molten salt method for the first time. It is found that with the prolonged time, the phase of NaLuF4 transforms from cubic to hexagonal, while the morphology changes from nanoparticles to microtubes then to microrods. Moreover, upon 980 nm laser diode (LD) excitation, white up-conversion (UC) light was successfully achieved by properly tuning the sensitizer (Yb3+) concentration in the host matrix. The relative emission intensities of different emission colors in Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+ doped β-NaLuF4 can be precisely adjusted in a broad range by tuning the Yb3+ doping concentration. Consequently, effective UC emissions with multicolors and a strong white light can be realized in β-NaLuF4:Yb3+/Er3+/Tm3+, and β-NaLuF4:Yb3+/Tm3+/Ho3+ structures by the appropriate control of the emission intensity balance for the three blue, green, and red basic colors. UC mechanisms in the co-doping and tri-doping β-NaLuF4 samples were analyzed in detail based on the emission spectra and the plot of luminescence intensity to pump power. The as-obtained abundant luminescence colors in a much wide region contribute themselves great potential applications in various fields. Furthermore, the paper also provides an effective and facile approach to gain a desired color by manipulating the sensitizer concentration.

Controllable white upconversion luminescence in Ho3+/Tm3+/Yb3+ co-doped CaMoO4

The polycrystalline Ho3+/Tm3+/Yb3+ co-doped CaMoO4 phosphors were successfully synthesized by complex citrate-gel method. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaMoO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 nm and 651 nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaMoO4 in the commission international de'eclairage (CIE) chromaticity diagram can be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. In Ho3+/Tm3+/Yb3+ co-doped CaMoO4, the UC luminescent properties on Tm3+ and Ho3+ concentrations and mechanism based on laser pump power were discussed in detail.

Tunable Multicolor Upconversion Emissions and Paramagnetic Property of Monodispersed Bifunctional Lanthanide-Doped NaGdF4 Nanorods

In this paper, highly monodispsered ultrasmall hexagonal phase NaGdF4 nanorods were synthesized via a hydrothermal method using oleic acid as a stabilizing agent. The tunable multicolor upconversion (UC) emissions, including green, yellow, blue, and white emissions, can be readily achieved from lanthanide (Ln)-doped NaGdF4 nanorods under the excitation of a 980 nm diode laser. The calculated chromaticity coordinates (CIE-X = 0.346, CIE-Y = 0.357) are close to those of the standard white light (CIE-X = 0.33, CIE-Y = 0.33), and the white UC emissions can be tuned from blue-white to white by adjusting the doped contents of Ho3+ in the Yb3+/Tm3+/Ho3+ triply doped NaGdF4 nanorods. In addition, the ultrasmall NaGdF4 nanocrystals also exhibit paramagnetic properties at 293 K. The measured magnetizations of the NaGdF4:20%Yb3+/0.2% Er3+ and NaGdF4 nanocrystals were about 1.49 and 1.86 emu/g at 20 kOe, respectively, which were close to the reported values of other nanoparticles for bioseparation. Moreover, the NaGdF4 nanocrystals can be readily attracted by a small magnet, which shows it has potential application in cell isolating. It is expected that these multifunctional ultrasmall NaGdF4 nanorods including tunable UC colors and intrinsic paramagnetic properties may have potential applications in color displays, biolables, bioseparation, and magnetic resonance imaging.