White Upconversion Research Articles

Structural and morphological characterizations of ex-situ sol-gel derived luminescent Nd3+-Yb3+ion co-doped zinc-silicate dense glass-ceramic

We proposed a novel ex-situ sol-gel synthesis of Nd3+ (0.7 mol%) and Yb3+ (X; X = 0.0, 0.7, 1.5, 3.0 mol%) ion co-doped Zinc-Silicate (SZNYX) dense glass-ceramic(DGC) samples. The structural analyses of the SZNY07-DGC sample were performed at different annealing temperatures using X-ray diffraction (XRD) analysis and Fourier transforms infrared (FTIR) spectroscopy. The tetragonal willemite Zn2SiO4 structure with an R-3(148) space group was confirmed from XRD results. The formation of the pure oxide phases (bridging oxygen) was noticed at FTIR spectra with the complete removal of hydroxyl impurity at higher annealing temperatures. The presence of ZnO crystallites with the inter-planer spacing of ⁓ 0.28 nm and Nd3+/Yb3+ ion pair in an amorphous silica host was confirmed via transmission electron microscopy (TEM) and TEM-energy dispersive spectroscopy (EDS) respectively. The white up-conversion luminescence (UCL) under a 980 nm excitation was attributed to the simultaneous emission of wavelength in the visible spectrum. The intensity of UCL was initially rising with an increase in Yb3+ ion concentration whereas the optimized luminescence was obtained for samples with 1.5 mol% Yb3+ ion concentration. The CIE chromaticity coordinates (0.34, 0.35) of corresponding UCL spectra were invariant with the change in Yb3+ ion concentration. The photoluminescence (PL) confocal mapping of the SZNY15-DGC sample was performed at different locations under a 980 nm laser excitation source which turned out non-uniform in nature throughout the surface. Thus as-synthesized SZNYX-DGC samples have spectacular upconversion luminescence for near-infrared excitation which may be utilized in thermal sensing, photovoltaic, displays, and photonic devices.

Upconversion white-light emission luminescence characteristics based on single-particle NaYF<sub>4 </sub>microrod

White upconversion (UC) luminescent materials have shown incomparable advantages over other light sources in the fields of solid-state lighting, liquid crystal display, and bioimaging, and received extensive attention from researchers. In this work, a series of microcrystals doped with different ion concentrations is synthesized by hydrothermal method, such as NaYF<sub>4</sub>: Yb<sup>3+</sup>/Ho<sup>3+</sup>/Tm<sup>3+</sup> and NaYF<sub>4</sub>: Yb<sup>3+</sup>/Ho<sup>3+</sup>/Tm<sup>3+</sup>, and their corresponding micron core-shell (CS) structures are constructed based on epitaxial growth technology. The structure and morphology of the prepared microcrystals are characterised by X-ray diffractometer (XRD) and scanning electron microscope (SEM), showing that the microcrystal has a pure hexagonal-phase crystal structure with a rod-like shape. Under the excitation of 980 nm near-infrared laser, the white UC luminescence characteristics of Ho<sup>3+</sup>/Tm<sup>3+</sup> and Er<sup>3+</sup>/Tm<sup>3+</sup> co-doped single-particle NaYF<sub>4</sub> microcrystals are systematically studied by modulating the concentration of the doping ions. The study shows that in Ho<sup>3+</sup>/Tm<sup>3+</sup> co-doped NaYF<sub>4</sub> microcrystals, white UC luminescence can be easily achieved by modulating the concentration of Yb<sup>3+</sup> ions, while in the Er<sup>3+</sup>/Tm<sup>3+</sup> co-doped NaYF<sub>4</sub> microcrystal, the white UC luminescence can be effectively achieved by modulating the concentration of Er<sup>3+</sup> ions. According to the luminescence characteristics of the microncrystals in different doping systems, the physical mechanism of white light emission regulation is revealed, which is mainly due to the interaction between the doped ions, including cross relaxation (CR) process and energy back transfer (EBT) process. Meanwhile, an effective enhancement of the white UC luminescence on CS microrod is achieved by coating the NaYF<sub>4</sub> inert shell. Therefore, ion doping technique and the construction of CS structure can not only realize the white UC luminescence of microrods, but also provide important experimental reference for further enhancing the luminescence characteristics of microrods, and expand the applications of microcrystals in the fields of display, optoelectronics and anti-counterfeiting.

White up-conversion La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors based on dual luminescence centers for high-sensitive optical thermometry

In this paper, the La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors are successfully synthesized through simple solid-state method. The white up-conversion luminescence is realized by appropriately varying the co-doped concentrations of Ho3+, Tm3+. The up-conversion luminescence characteristics and energy transfer processes of La2Mo2O9:Yb3+, Ho3+, Tm3+ are specifically analyzed upon 980 nm laser excitation. A strategy to enhance the optical temperature sensing performance is demonstrated via flexibly selecting diverse non-thermally coupled energy levels of dual luminescence centers with the fluorescence intensity ratio technology. The maximum values of absolute and relative sensitivity for the thermometer reach 0.2478 K−1 and 1.38% K−1 based on the non-thermally coupled energy levels of 3F2,3 (Tm3+)/5S2,5F4 (Ho3+). The luminescence color of La2Mo2O9:Yb3+, Ho3+, Tm3+ phosphors can maintain in the white region over the whole measured temperature range. These results indicate that the phosphors possess great potential in broad application prospects in the aspects of anti-counterfeiting, displays and non-contact temperature sensing.

High-sensitive temperature sensing based on thermal-enhanced emission and non-thermally coupled energy levels of white upconversion luminescence system

Na3Y(VO4)2:Nd3+,Yb3+,Ho3+,Tm3+ phosphors present significantly improved sensitivity of optical temperature sensing based on thermal-enhanced upconversion luminescence and non-thermally coupled energy levels. Under 808 nm excitation, white upconversion luminescence is successfully achieved in Nd3+-sensitized system. In addition, the emissions intensities originated from 4G5/2→4I9/2 transition of Nd3+ and 3F2,3→3H6 transition of Tm3+ gradually increase with elevating temperature owning to the thermal population effects, as opposed to the blue (1G4→3H6 transition of Tm3+), green (5S2,5F4→5I8 transition of Ho3+) and red (5F5→5I8 transition of Ho3+) emissions intensities show continuous decreasing trend. The temperature sensing behaviors are investigated by employing multiple non-thermally coupled energy levels. Based on non-thermally coupled energy levels of 4G5/2 (Nd3+)/1G4 (Tm3+), the absolute and relative sensitivities are obtained to be 0.433 K−1 and 2.81 % K−1. These results demonstrate that the Na3Y(VO4)2:Nd3+,Yb3+,Ho3+,Tm3+ phosphors with superior optical thermometry performance and white luminescence within a relatively wide temperature range can achieve optical applications in many fields.

White-light emission in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles

Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles were synthesized using a microwave hydrothermal method and studied for white-light emission under 980 nm laser diode excitation. White upconversion (UC) light was successfully obtained with the appropriate control of blue, green, and red emissions by successfully tuning the Er3+ and Ho3+ concentrations in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4, respectively. In addition, the white color emission was shown by the CIE chromaticity coordinates of samples. The energy transfer mechanisms are explained in detail based on the emission spectra and pump power density-dependent UC luminescence intensity in rare earth (Yb3+/Er3+/Tm3+ and Yb3+/Er3+/Tm3+/Ho3+)-doped α-NiMoO4 nanoparticles. The results indicate that Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles can be good candidates for white-light devices.

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 up-conversion luminescence and highly-sensitive optical temperature sensing in Na3La(VO4)2:Yb,Er,Tm,Ho phosphors

In this work, tunable white up-conversion luminescence was achieved in the Yb3+, Er3+, Tm3+, Ho3+ co-doped Na3La(VO4)2 phosphors under 980 nm excitation. The emissions of three primary colors are mainly attributed to the 2H11/2/4S3/2 → 4I15/2 transitions of Er3+, 1G4→3H6 transition of Tm3+, and 5F5→5I8 transition of Ho3+. White luminescence characteristics and mechanisms of up-conversion system were investigated in detail. In addition, the temperature sensing behaviors of multiple levels emission combinations for Na3La(VO4)2:Yb3+,Er3+,Tm3+,Ho3+ were analyzed by employing thermally coupled and non-thermally coupled energy levels. Based on the emissions of 3F2,3/1G4 energy levels, the maximum relative and absolute sensitivities were obtained to be 2.20%/K and 0.279 K–1. The design of up-conversion luminescence materials with high-quality white luminescence and excellent sensitivity performance is critical in the field of optical applications.

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

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

White up-conversion luminescence properties in Yb3+/Ho3+/Tm3+ tri-doped LiGaW2O8 phosphors

Monoclinic Yb 3+ -Tm 3+ -Ho 3+ tri-doped LiGaW 2 O 8 phosphors were prepared by the high temperature solid-state method. Upon the excitation of 980 nm, up-conversion (UC) blue emission in Tm 3+ /Yb 3+ co-doped and green and red emissions in Ho 3+ /Yb 3+ co-doped LiGaW 2 O 8 were observed, respectively. Bright white luminescence could be obtained by changing the doped concentrations of Tm 3+ ions in Tm 3+ /Ho 3+ /Yb 3+ co-doped LiGaW 2 O 8 . Moreover, based on the power dependence of the luminescence intensity, the UC mechanisms were studied. The results demonstrate that the multi-colors of the LiGaW 2 O 8 :Tm 3+ ,Ho 3+ ,Yb 3+ could be used in the fields of three-dimensional displays, solid-state lighting, and backlighting such as the white light generation. • The white UC properties of Yb 3+ -Tm 3+ -Ho 3+ tri-doped LiGaW 2 O 8 phosphors were researched for the first time. • Blue emission, green emission and red emission could be obtained in the LiGaW 2 O 8 : Tm 3+ , Ho 3+ , Yb 3+ phosphors. • Bright white luminescence upon 980 nm can be generated through an UC process in Tm 3+ /Ho 3+ /Yb 3+ co-doped LiGaW 2 O 8 .

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.

Synthesis and Application in Anticounterfeiting of RGB Upconversion Nanoparticles

In this paper, we synthesized ~105±15 nm cubic phase KMnF3:Yb3+,Er3+ NPs, ~195±10 nm hexagonal phase NaYF4:Yb3+,Tm3+ NPs, and ~200±10 nm hexagonal phase NaYF4:Yb3+,Er3+ NPs. Under the excitation of 980 nm, the strong red upconversion luminescence (4F9/2⟶4I15/2, the peak is located at ~653 nm) of Er3+ ions of KMnF3:Yb3+,Er3+ NPs can be seen, the strong blue upconversion luminescence (1D2⟶3F4, 1G4⟶3H6; the peaks are located at ~451 nm and ~477 nm, respectively) of Tm3+ ions of NaYF4:Yb3+,Tm3+ NPs can be observed, and the strong green upconversion luminescence (4I11/2⟶4I15/2, 4S3/2⟶4I15/2; the peaks are located at ~524 nm and ~541 nm, respectively) of Er3+ ions of NaYF4:Yb3+,Er3+ NPs can be found. The mixed white upconversion luminescent materials can be obtained by adjusting the doping ratio of the above NPs. Cyclohexane solution of red, blue, green, and the mixed white NPs can be used as ink, and “JLNU” is written on paper with a pen. Without 980 nm radiation, nothing could be seen. Under 980 nm irradiation, the colored letters “JLNU” can be seen. Red, blue, green, and the mixed white upconversion NPs can be used in security anticounterfeiting.

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.

Multicolor Tunable Upconversion Luminescence from Sensitized Seed-Mediated Grown LiGdF4:Yb,Tm-Based Core/Triple-Shell Nanophosphors for Transparent Displays

Red, green, blue, and natural white upconversion (UC) luminescence colors are realized from the tetragonal-structured LiGdF4-based core/triple-shell (C/T-S) upconversion nanophosphors (UCNPs) and the C/T-S UCNP-incorporated polymer composites. The LiYF4:Yb cores are used as sensitized seeds for the formation of LiGdF4:Yb,Tm UC shell followed by the growth of LiGdF4:Tb,Eu color tuning shell. Finally, LiYF4 inert shell is grown on the core/shell/shell UCNPs, and LiYF4:Yb/LiGdF4:Yb,Tm/LiGdF4:Tb,Eu/LiYF4 C/T-S UCNPs exhibit enhanced UC luminescence. The single tetragonal-phased C/T-S UCNPs exhibit blue, green, and red UC luminescence, which is attributed to the electronic transitions in Tm3+ via energy transfer UC process and Tb3+ and Eu3+ via energy migration UC process, respectively. The multicolor UC emissions, including natural white, medium aquamarine, purple, and thistle color, are created by fine-tuning of the ratio of Tb3+ and Eu3+ in the color tuning shell. The transparent polymer composites are prep...

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.