Bright White Upconversion Research Articles

Tunable multicolor and bright white upconversion luminescence in Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 phosphors

A series of Er3+, Tm3+, Yb3+ co-doped or tri-doped SrLu2O4 phosphors were synthesized by a high-temperature solid-state reaction method. The crystal structure was characterized by X-ray diffraction technique and further validated by Rietveld refinement. The chemical composition and elemental distribution of tri-doped sample were determined by the energy-dispersive spectrometry. It is worthwhile to note that the upconversion (UC) luminescence of as-prepared samples could be precisely controlled by adjusting the Yb3+ doping concentration and the excitation pump power. A bright UC white light in Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 samples was observed by controlling the intensities of red, green and blue emissions. Under various pump powers in the range of 290–810 mW, the color coordinates could be effectively tuned in a quite broad white region. Particularly, the color coordinate of optimal sample under 630 mW at 980-nm excitation is (0.3336, 0.3244), which is very close to the standard white-light illumination (0.333, 0.333) and the corresponding correlated color temperature is 5442 K. Based on the UC emission spectra and luminescence decay curves, the energy transfer (ET) mechanisms involved in the different UC processes were proposed in detail. The results imply that ET processes of Yb3+ → Er3+, Yb3+ → Tm3+ and Tm3+ → Er3+ worked simultaneously in tri-doped system and produced white UC emissions by means of two- or three-photon processes. The Er3+/Tm3+/Yb3+ tri-doped SrLu2O4 phosphor can be a potential candidate for white UC material in displays, backlights and white-light sources.

Bright white upconversion luminescence from Er3+/Tm3+/Yb3+-doped titanate-based glasses prepared by aerodynamic levitation method

Aerodynamic levitation method was employed to prepare Er3+/Tm3+/Yb3+-doped titanate-based glasses. DTA results show that the glass performs high thermal stability with the glass transition temperature of 799 °C. The interaction among rare earth ions has been discussed by adjusting the relative concentration. Er3+ ions can quench the upconversion luminescence of Tm3+ ions. Tm3+ ions play a strong role in quenching the emissions of Er3+ and Tm3+ when the content of Tm3+ ions is greater than or equal 0.05. From the view of the ratio of red emission to green emission, Tm3+ ions can improve the red emission of Er3+ ions to some extent in contrast with the green emissions of Er3+ ions. 980 nm incident laser can be efficiently absorbed by Yb3+ ions. The relative intensity of red, green, and blue upconversion luminescence has been tuned to obtain white light. The composition with white upconversion luminescence of the color coordinate (0.291, 0.3292) has been found. Moreover, white upconversion luminescence mechanism is a two-photon process of ET, ESA, and cooperative sensitization. Rare earth ions doped titanate-based glasses with bright upconversion luminescence perform potential applications in color display, back light, et al.

Upconversion luminescence of Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 phosphors

The polycrystalline Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 phosphors were successfully synthesized by the simple solid-state reaction method. Under the laser excitation of a 980nm, Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 showed bright white upconversion (UC) emission visible to the naked eyes, which composes of blue emission at 475nm from Tm3+, green and red emissions at 540nm and 651nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped NaLa(MoO4)2 in the commission international de׳eclairage (CIE) chromaticity diagram could be controlled from cool to warm white color depending on Ho3+ and Tm3+ concentrations. The luminescent properties on Tm3+ and Ho3+ concentrations and UC mechanism based on laser pump power were discussed in detail.

White luminescence of Ho3+/Tm3+/Yb3+-codoped CaWO4 synthesized via citrate complex route assisted by microwave irradiation

The nanocrystalline Ho3+/Tm3+/Yb3+ co-doped CaWO4 upconversion (UC) phosphors were successfully synthesized by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperature ranging from 300 to 700 °C for 3 h. Crystallization of the Ho3+/Tm3+/Yb3+ co-doped CaWO4 was detected at 400 °C, and entirely completed at 600 °C. The Ho3+/Tm3+/Yb3+ co-doped CaWO4 heat-treated at 600 °C showed primarily spherical and homogeneous morphology. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaWO4 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 and 651 nm respectively from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaWO4 in the Commission International De'eclairage (CIE) chromaticity diagram could be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. The UC luminescent properties on Tm3+ and Ho3+ concentrations and related mechanism based on laser pump power were discussed in detail.

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.

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.

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.

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.

Bright white upconversion luminescence from Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 powders

Bright white upconversion luminescence from Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 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 Er 3+ ions and 1G 4 → 3H 6 of Tm 3+ ions, respectively. The efficient upconversion emission is attributed to the energy transfer between Yb 3+ and Er 3+ or Tm 3+ions. Moreover, it is observed that Tm 3+ acts as the quenching center for the green upconversion luminescence from Er 3+ ions, and the sensitizer for the red and blue luminescence when the Tm 3+ doping content is less than 0.3 mol%. This is interpreted in terms of the efficient energy transfer between Tm 3+ and Er 3+ ions. The calculated color coordinates fall within the white region in the standard 1931 CIE chromaticity diagram, indicating the potential applications of Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 in the field of displaying and lasers, etc.

Bright White Upconversion Luminescence in β-NaGd0.794Yb0.20Ho0.001Tm0.005F4 Nanoparticles

Abstract β-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles were synthesized through a simple hydrothermal method. The nanoparticles crystallized well and exhibited nearly hexagonal morphology and ellipsoidal spheres, as characterized by X-ray powder diffraction and transmission electron microscopy. The β-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles have an average size of about 23 nm. Room-temperature bright white upconversion luminescence in β-NaGd0.794Yb0.20Ho0.001Tm0.005F4 nanoparticles was obtained under single-wavelength diode laser excitation of 980 nm.

Bright white upconversion emission from Yb3+, Er3+, and Tm3+-codoped Gd2O3 nanotubes

Yb(3+), Er(3+), and Tm(3+)-codoped Gd(2)O(3) nanotubes were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. X-Ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), upconversion (UC) emission spectra, and kinetic decay were used to characterize the samples. Bright white UC luminescence in the nanotubes was observed under diode laser excitation of 980 nm. The white light consists of the blue ((1)G(4)-->(3)H(6) of Tm(3+)), green ((2)H(11/2)/(4)S(3/2)-->(4)I(15/2) of Er(3+)), and red ((4)F(9/2)-->(4)I(15/2) of Er(3+)) UC emissions. As the excitation power density changed in the range of 20-200 W cm(-2), the calculated CIE color coordinates shift only slightly and fall well within the white region. This material may be a potential candidate for applications of color displays, lighting and photonics.

Controllable Red, Green, Blue (RGB) and Bright White Upconversion Luminescence of Lu2O3:Yb3+/Er3+/Tm3+ Nanocrystals through Single Laser Excitation at 980 nm

Light fantastic! Lu(2)O(3):Yb(3+)/Er(3+)/Tm(3+) nanocrystals with controllable red, green, blue (RGB) and bright white upconversion luminescence by a single laser excitation of 980 nm have been successfully synthesized (see picture). Due to abundant UC PL colors, it can potentially be used as fluorophores in the field of color displays, back light, UC lasers, photonics, and biomedicine.Lu(2)O(3):Yb(3+)/Er(3+)/Tm(3+) nanocrystals have been successfully synthesized by a solvothermal process followed by a subsequent heat treatment at 800 degrees C. Powder X-ray diffraction, transmission electron microscopy, upconversion photoluminescence spectra, and kinetic decay were used to characterize the samples. Under single-wavelength diode laser excitation of 980 nm, the bright blue emissions of Lu(2)O(3):Yb(3+), Tm(3+) nanocrystals near 477 and 490 nm were observed due to the (1)G(4)-->(3)H(6) transition of Tm(3+). The bright green UC emissions of Lu(2)O(3):Er(3+) nanocrystals appeared near 540 and 565 nm were observed and assigned to the (2)H(11/2)-->(4)I(15/2) and (4)S(3/2)-->(4)I(15/2) transitions, respectively, of Er(3+). The ratio of the intensity of green luminescence to that of red luminescence decreases with an increase of concentration of Yb(3+) in Lu(2)O(3):Er(3+) nanocrystals. In sufficient quantities of Yb(3+) with resprct to Er(3+), the bright red UC emission of Lu(2)O(3):Yb(3+)/Er(3+) centered at 662 nm was predominant, due to the (4)F(9/2)-->(4)I(15/2) transition of Er(3+). Based on the generation of red, green, and blue emissions in the different doped Lu(2)O(3):RE(3+) nanocrystals, it is possible to produce the luminescence with a wide spectrum of colors, including white, by the appropriate doping of Yb(3+), Tm(3+), and Er(3+) in the present Lu(2)O(3) nanocrystals. Namely, Lu(2)O(3):3 %Yb(3+)/0.2 %Tm(3+)/0.4 %Er(3+) nanocrystals show suitable intensities of blue, green, and red (RGB) emission, resulting in the production of perfect and bright white light with CIE-x=0.3456 and CIE-y=0.3179, which is very close to the standard equal energy white light illuminate (x=0.33, y=0.33). Because of abundant luminescent colors from RGB to white in Lu(2)O(3):Yb(3+)/Er(3+)/Tm(3+) nanocrystals under 980 nm laser diode (LD) excitation, they can potentially be used as fluorophores in the field of color displays, back light, UC lasers, photonics, and biomedicine.

White upconversion of rare-earth doped ZnO nanocrystals and its dependence on size of crystal particles and content of Yb3+ and Tm3+

Rare earth (RE) doped ZnO nanocrystals were synthesized by chemical combustion method. Bright white upconversion (UC) luminescence with the CIE coordinates close to (0.33, 0.33) was obtained in Er+Tm+Yb tridoped ZnO nanocrystals under the excitation of a cost-effective 980 nm single-wavelength laser diode. The overall and relative UC luminescence intensities of RE doped ZnO nanocrystals were found to be depended highly on the diameter of crystal particles and the concentration of Yb3+ and Tm3+, for which the involved mechanisms were demonstrated. The investigation based on UC spectra, simplified energy level diagram, and excitation power dependence indicated that the remarkable enhancement of the green emission of the RE tridoped sample was due to a dual sensitization of Er3+ by Yb3+ and Tm3+ ions. The RE tridoped ZnO nanocrystals with the CIE coordinates close to (0.33, 0.33) are potentially suitable for the widely realistic application as the multicolor fluorescent labels, due to a fact that they could be cheaply and easily obtained and excited cost effectively.

White Up-Conversion Luminescence in Rare-Earth-Ion-Doped YAlO3 Nanocrystals

Room-temperature bright white up-conversion (UC) luminescence in Yb 3+ /Er 3+ /Tm 3+ ion-doped YAIO 3 nanocrystals was achieved under diode laser excitation of 974.5 nm. The white light consists of the blue ( 1 G 4 → 3 H 6 of Tm 3+ ), green ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 of Er 3+ ), and red ( 1 G 4 → 3 F 4 of Tm 3+ and 4 F 9/2 → 4 I 15/2 of Er 3+ ) UC emissions. The UC mechanisms were proposed based on spectral, pump power dependence and kinetic analyses. The white light may be a possible candidate for applications in the field of lighting, displays, and photonics.

Bright white upconversion luminescence in rare-earth-ion-doped Y2O3 nanocrystals

Room temperature bright white upconversion (UC) luminescence in Yb3+–Tm3+–Er3+ ions doped Y2O3 nanocrystals was obtained under single-wavelength diode laser excitation of 976nm. The white light consists of the blue, green, and red UC radiations which correspond to the transitions G41→H63 of Tm3+, H11∕22∕S3∕24→I15∕24, and F9∕24→I15∕24 of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses. The calculated color coordinates display that white light can be achieved in a wide range of pumping powers, which promises their potential applications in the field of displays, lasers, photonics, and biomedicine.