White Upconversion Emission Research Articles

Lanthanide-doped nanocrystals in high-Q microtoroids for stable on-chip white-light lasers

The plentiful energy states of lanthanide ( Ln 3 + )-doped nanomaterials make them very promising for on-chip integrated white-light lasers. Despite the rapid progresses, the Ln 3 + -based white upconversion emissions are strongly restricted by their low upconversion quantum efficiency and the color stability. Herein, we combine the CaF 2 : Yb 35 Tm 1.5 Er 0.5 nanocrystals and the high- Q microtoroids, and experimentally demonstrate the chip-integrated stable white-light laser. By optimizing the sizes, density, and distributions of Ln 3 + -doped nanocrystals, the Q factors of Ln 3 + -doped microtoroids are maintained as high as 5 × 10 5 . The strong light matter interaction in high- Q microtoroids greatly enhances the upconversion emission and dramatically reduces the laser thresholds at 652 nm, 545 nm, and 475 nm to similarly low values ( 1.89 – 2.10 mJ cm − 2 ). Consequently, robust white-light microlaser has been experimentally achieved from a single microtoroid. This research has paved a solid step toward the chip-scale integrated broadband microlasers.

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y2O3:R(R = Yb3+, Er3+, Tm3+) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er3+/5 mol% Yb3+/xTm3+ tri-doped Y2O3 nanophosphors were sintered at 1000 °C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm3+ concentration from 0 to 0.5 mol%, because the Tm3+ state can be easily reached due to the 2F7/2 → 2F5/2 transition of Yb3+ near 10,000 cm−1. The Y2O3: Er3+/Yb3+/Tm3+ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.

White upconversion emission in CaHfO3 with codoping of Er3+, Ho3+, and Tm3+

White upconversion emission in CaHfO3 with codoping of Er3+, Ho3+, and Tm3+

Efficient white upconversion luminescence in Yb3+/Eu3+ doubly-doped transparent glass ceramic.

Efficient white upconversion (UC) luminescence is obtained in Yb3+/Eu3+ doubly-doped optical glass ceramic (GC) for the first time. KYb3F10 nanocrystals are controllably precipitated from the amorphous networks via the inducing of Yb3+. Yb3+ ions are spontaneously confined within the compact fluoride crystal structures to produce efficient blue UC emissions of Yb3+-Yb3+ pairs. Eu3+ ions are easily incorporated into the KYb3F10 crystal lattices. Owing to the extremely short interionic distance in the crystal structures, intense green UC emissions apart from the red emissions of Eu3+ are observed, which are not obtained by the traditional Yb3+/Eu3+ doubly-doped GCs. As a result, white UC emissions are synthesized based on the three-primary-color principle and the emission intensities of GCs are dramatically enhanced as compared to glass. The designed GCs provide novel optical gain materials for the promising applications in three-dimensional display, solid-state lighting and tunable fiber lasers.

Tunable and white up-conversion emission from Tm3+-Ho3+-Yb3+/-Nd3+ co-doped GdVO4 phosphors under 808-nm excitation

Lanthanide-doped system with adjustable multicolor and white up-conversion (UC) emission has been developed in GdVO4 (GVO): Tm3+-Ho3+-Yb3+/-Nd3+ phosphors, which are fabricated via a facile solid-state reaction. Herein, we study their phase structures and the Ho3+ concentration effect on their up-conversion emission. Under 980 nm excitation, the Tm3+-Ho3+-Yb3+ tri-doped GVO phosphors exhibit intense luminescence combined with red, green and blue (RGB) emission and the successive energy transfer between Tm3+-Ho3+-Yb3+ ions causes a slight shift in the color coordinates of samples with different doping concentrations. Under 808 nm excitation, the color coordinate of the optimum GVO: Tm3+-Ho3+-Yb3+-Nd3+ phosphor is located at (0.3277, 0.3433), which is closest to the ideal white light emission corresponding to (0.3333, 0.3333). Therefore, it is proved that these phosphors provide potential applications in the fields of displays, lasers and optical telecommunication.

Warm white broadband emission and tunable long lifetimes in Yb3+ doped Gd2O3 nanoparticles

Upconversion luminescence materials have stimulated growing attention in photovoltaic cell owning to the ability of converting a few low-energy photons into a single high-energy photon. However, there still remains a daunting challenge to achieve upconversion emission covering the entire visible spectrum in a single material. Here, an incandescent broadband white upconversion emission covering the entire visible region is realized in a single Gd2O3:Yb3+ nanoparticles by utilization of adverse multiphonon relaxation. Importantly, tunable long fluorescence lifetime can be synchronously implemented in the single material, where the lifetime range spans one order of magnitude. Furthermore, benefiting from the broadband emission, the luminescence intensity achieves 482-fold improvement as the power increase from 0.53 W to 1.51 W. These broadband emissions are enabled by engineering the pathways of nonradiative de-excitation via multiphonon relaxation. Based on the kinetic analysis and mechanism research, the photon avalanche is demonstrated to play an important role for broadband emission. The warm white emission together with its tunable long lifetime provides a new avenue for developing single emitter-based white-light-emission materials for next-generation display and lighting technologies.

Color thermal stability of white up-conversion luminescent emission in Eu3+/Yb3+ co-doped YOF phosphor

The Eu3+/Yb3+ co-doped YOF phosphor is synthesized via the hydrothermal method. The intense blue, green and red up-conversion emission of the phosphor can be radiated at 980 nm excitation. The up-conversion emission color adjustment from yellow to blue is realized through cooperative sensitization up-conversion process by altering the excitation power and pulse width of 980 nm pulse laser. Especially, the white up-conversion emission of the phosphor can be generated under 980 nm continuous laser and pulse laser irradiation. The corresponding energy transfer mechanism of Eu3+/Yb3+ co-doped YOF phosphor has been proposed in this work. The influence of temperature on up-conversion luminescent emission color is explored under the condition that can generate optimal white emission. The excellent color thermal stability of white up-conversion emission can be found at continuous high temperature. Strong white emission at high temperature and multicolor emissions of the phosphor make the phosphor suitable for using in high temperature environment for white light illuminating and color displaying application.

Up-Conversion Nanoparticles/PMMA Composites for Light-Emitting Applications

In this paper, we prepared KMnF3:Yb[Formula: see text], Er[Formula: see text] nanoparticles (NPs)/polymethyl methacrylate (PMMA) composites, NaYF4:Yb[Formula: see text], Tm[Formula: see text]NPs/PMMA composites and NaYF4Yb[Formula: see text], Er[Formula: see text]NPs/PMMA composites by in situ polymerization, and these NPs/PMMA composites can emit red, blue and green up-conversion fluorescence excited by 980[Formula: see text]nm, respectively. The mixed white NPs/PMMA composites were obtained by adjusting the doping ratio of the above three NPs. These NPs/PMMA composites are transparent. We tested the up-conversion fluorescence spectra of all the NPs and NPs/PMMA composites, under 980[Formula: see text]nm excitation. The up-conversion luminescence spectra of the NPs and NPs/PMMA composites are consistent, which further indicates that the in situ polymerization has not changed the chemical structure of the NPs. Then, we prepared transparent bulk polymers by curing these NPs/PMMA composites. Under 980[Formula: see text]nm laser excitation, these NPs/PMMA bulk polymers can emit red, blue, green and white up-conversion emissions, respectively. The results indicate that the NPs/PMMA composites can be applied to three-dimensional (3D) display.

Tunable multicolor and white emission NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures

A facile and surfactant-free molten salt method has been proposed to prepare a well-defined one-dimensional NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ nanorods for the first time. It is found that by properly tuning the sensitizer (Nd3+) concentration in the host matrix upon 980 nm laser diode (LD) excitation, white up-conversion (UC) emission was achieved. Also, by doping Yb3+/Er3+/Tm3+/Nd3+ in NaLuF4 the relative intensities of different emissions can be precisely adjusted in a broad range. Consequently, by appropriately controlling the emission intensity balance of blue, green and red basic colors in multicolor UC emissions, a strong white light can be realized in NaLuF4:Yb3+, Er3+,Tm3+,Nd3+ structures. UC mechanisms were analyzed in detail based on the emission spectra. The as-synthesized abundant luminescence colors in a wide region contribute themselves great potential applications. Furthermore, by manipulating the sensitizer concentration the paper provides an effective and facile method to gain a desired color.

White up-conversion efficiency of Yb3+/Er3+/Tm3+ co-doped β-NaYF4 nano-crystals

In this paper, Yb3+/Er3+, Yb3+/Tm3+ and Yb3+/Er3+/Tm3+ co-doped β-NaYF4 up-conversion fluorescent nanoparticles (UCNPs) with an average diameter of 50 nm were successfully synthesized through a thermal decomposition method. The Yb3+/Er3+ co-doped UCNPs possess bright and tunable luminescence varying from green to red as the ratio of Yb3+ and Er3+ doping increases. Remarkably, white up-conversion luminescence can be successfully achieved through the incorporation of Tm3+. The white light up-conversion efficiency of Yb3+/Er3+/Tm3+ co-doped UCNPs dispersed in the solvent have been calculated, suggesting the potentials of the efficient white up-conversion emissions for the multispectral imaging and potential bio-applications.

Tuning white upconversion emission in GdPO4:Er/Yb/Tm phosphors

Nanoscale phosphors of Yb3+/Er3+/Tm3+-doped GdPO4 with different morphologies were synthesized using the solvothermal method with annealing at 750 °C and 1000 °C. A high concentration of Yb3+(35%mol) ions was successfully doped in the powders. Crystal structures were characterized through powder XRD measurement and Fourier transform infrared spectroscopy. SEM images have shown that the morphologies of the samples can be controlled by adjusting the pH value during their synthesis. Upconversion luminescence was investigated under 980 nm diode laser excitation. The upconversion processes were assessed on the basis of the power dependence of upconversion emission intensity. The light colour was investigated with respect to the 1931 CIE diagram. The samples show good emission tunability by monitoring the annealing temperature and the diode laser pump intensity. By properly adjusting the excitation power, white upconversion luminescence can be attained. Yb3+/Er3+/Tm3+-doped GdPO4 nanophosphors appear, which have potential applications in the field of upconversion-based white lighting devices.

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.

Exploiting the silent upconversion emissions from a single β-NaYF4:Yb/Er microcrystal via saturated excitation

Achieving intense nearly white upconversion emission from a single β-NaYF4:Yb/Er microcrystal via saturated excitation.

Ultraviolet and Visible Upconversion Emissions in Er3+-Yb3+ Doped Titanium Dioxide Nanopowder under the 980 nm Laser Diode Excitation

Er3+-Yb3+ co-doped titanium dioxide upconversion nanoparticles were synthesized by Sol-gel method. White upconversion emissions were observed after excitation of nanoparticles with 980 nm Near-Infrared laser diode. Upconversion emissions consist of red (640-690 nm), green (520-570 nm) and blue (408 nm) emissions. Ultraviolet upconversion emissions were also detected with wavelength about 210 nm. Ultraviolet emissions are probably the results of relaxation from 2I13/2 (220 nm) and 2L15/2 (210 nm) states to 4I15/2. Visible and ultraviolet emissions of these nanoparticles can be used in photodynamic therapy. High penetration of Near-Infrared light into the body tissue makes these nanoparticles appropriate for aiming tumors in deeper tissues in comparison with older methods of photodynamic therapy.

Upconversion Emission Modification and White Light Generation in NaYF4:Yb3+, Er3+, Tm3+Nanocrystals/Opal Photonic Crystal Composites

In this paper, we fabricated NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystal/opal photonic crystal composites by depositing NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals on the surface of opal photonic crystals, and we investigated the influence of photonic bandgaps on upconversion (UC) emission properties of NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals. When the photonic bandgaps overlapped with the UC emission bands of NaYF 4:Yb 3+, Er 3+, Tm 3+ nanocrystals on the opal photonic crystal surfaces, the suppression or enhancement of UC emissions was observed due to the Bragg reflection effect of photonic crystal, resulting in the modification of red, green, and blue UC emissions. Thus, white UC emission was realized.

White-light upconversion emissions and color tunability of 12CaO·7Al_2O_3:Ho^3+/Yb^3+/Tm^3+ single crystal

Ho3+/Yb3+/Tm3+ codoped 12CaO·7Al2O3 single crystal exhibiting upconversion white light under 980nm excitation have been successfully prepared by Czochralski method. CIE coordinate of 0.4mol%Ho3+/2.0mol%Yb3+/0.5mol%Tm3+/C12A7 single crystal under 980nm excitation of 800mW is (0.35, 0.33), which is very close to the white emission center (0.33, 0.33). The color of the upconversion luminescence can be changed by simply adjusting the excitation power. The pump dependence and luminescent decay dynamics suggest that the blue upconversion emissions are populated by a three-photon process, the green emissions are two-photon process, and the red emissions are a combination of two and three photons processes. The upconversion mechanism is analyzed in detail. 12CaO·7Al2O3 single crystal with white upconversion emissions is expected to have broad application prospects in solid-state multicolor display and instrument integration.

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.

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.