Multicolor Upconversion Emission Research Articles

Multi-color Na3GaF6:Tm3+,Yb3+@SiO2 for dual-mode security and information encryption

The development of advanced luminescent materials is important for anti-counterfeiting applications, but still faces many challenges. In this study, Na3GaF6:Tm3+,Yb3+@SiO2 core@shell type nanocrystals with cryolite structure were synthesized for the first time by co-precipitation method. By modulating the excitation mode and Tm3+/Yb3+ doping ratio, the Na3GaF6:Tm3+,Yb3+@SiO2 nanocrystals exhibits multicolor up-conversion emission. Multicolor anti-counterfeiting ink was configured with up-conversion nanocrystals, and a variety of multi-colour anti-counterfeiting patterns were printed using screen printing technology. Additionally, multi-colour fluorescent barcodes are combined with binary coding technology to achieve encryption of anti-counterfeiting information. This work not only discovered an excellent up-conversion nanocrystals (Na3GaF6:Tm3+,Yb3+@SiO2) suitable for anti-counterfeiting applications, but also provided an effective encryption strategy for anti-counterfeiting information.

Dynamic modulation of multicolor upconversion luminescence of Er3+ via excitation pulse width.

Lanthanide-doped upconversion (UC) luminescent materials display multicolor emissions, making them ideal for a variety of applications, such as multi-channel biological imaging, fluorescence encryption, anti-counterfeiting, and 3D display. Manipulating the UC emissions of the luminescent materials with a fixed composition is crucial for their applications. Herein, we propose a facile strategy to achieve pulse-width-dependent multicolor UC emissions in NaYF4:Yb/Er/Tm nanocrystals. Upon excitation with a 980nm continuous-wave laser diode, Er3+ ions in NaYF4:20%Yb,15%Er,1%Tm nanocrystals exhibited UC emissions with a red-to-green (R/G) ratio of 11.3. Nevertheless, by employing a 980nm pulse laser with pulse widths from 0.1 to 10ms, the UC R/G ratio can be easily adjusted from 0.9 to 11.3, resulting in continuous and remarkable color transformation from green, yellow, orange, to red. By virtue of the dynamic luminescence color variation of these NaYF4:20%Yb,15%Er,1%Tm nanocrystals, we demonstrated their potential applications in the areas of anti-counterfeiting and information encryption. These findings provide deep insights into the excited-state dynamics and energy transfer of Er3+ in NaYF4:Yb/Er/Tm nanocrystals upon 980nm pulse excitation, which may pave the way for designing multicolor UC materials toward versatile applications.

Multicolor and multimodal luminescence in an Er3+ single-doped double perovskite for advanced anti-counterfeiting and encryption

The Er3+ single-doped NaGdTi1.8Al0.2O6 double perovskite material achieves multicolor luminescence, afterglow, and upconversion emission by responding to several types of excitation ranging from UV to NIR and thermal disturbance.

Activating ultralow upconversion nanothermometry in neodymium sublattice for heart tissue imaging rapid-responsive

The fields of biosensitivity and biological imaging have received a lot of attention from rare earth-doped upconversion nanoparticles (UCNPs). However, owing to the relatively large energy difference of rare earth ions, biological sensitivity based on UCNPs is restricted to detect at low temperature. Here, we design core-shell-shell NaErF4:Yb@Nd2O3@SiO2 UCNPs as a dual-mode bioprobe that produces blue, green, and red multi-color upconversion emissions at extremely low temperatures between 100 K and 280 K. Based on the thermally coupled energy levels (TCELs) of Er3+ (2H11/2 and 4S3/2) and Nd3+ (4F5/2 and 4F3/2) at 100 K, the greatest relative sensitivity (SR) approaches 12.7% K−1. NaErF4:Yb@Nd2O3@SiO2 injection is used to achieve blue upconversion emission imaging of frozen heart tissue, showing that this UCNP can serve as a low-temperature sensitive biological fluorescence.

Luminescence Temperature Sensing and First Principles Calculation of Photoelectric Properties in C12A7 Co-Doped Eu3+ Ions.

Developing high-resolution, high-accuracy fluorescent thermometers is challenging. In this study, the optical properties and thermal sensing of Yb-, Tm-, and Eu-co-doped C12A7 (C12A7:Yb/Eu/Tm), with flower-like structure upconversion microparticles, were studied. Eu3+ doping induced an approximately 6-fold change in the upconversion luminescence (UCL) output in comparison with C12A7:Yb/Tm microparticles. The maximum relative temperature sensitivity (S) of C12A7:Yb/Eu/Tm reached 3.0% K-1, representing an approximately 5-fold difference compared with the value of C12A7:Yb/Tm. In particular, the multicolor upconversion emission of C12A7:Yb/Eu/Tm can easily change from blue to white UCL with increasing temperature. Moreover, the band structure, total density, and optical coefficient of C12A7:Yb/Eu/Tm were investigated via density functional theory. The total density of O atoms increased in comparison with the total density of pure C12A7, indicating that substitution of Ca2+ by Yb/Eu/Tm produced positive vacancies on the cage structure. The optical coefficient of C12A7 was improved by the Yb/Eu/Tm dopant. The thermally regulated multicolor characteristics and thermally coupled energy levels of Tm3+ provide "dual adjustment temperature sensing", which is a promising strategy for realizing accurate and effective temperature sensors.

Unique excitation power density and pulse width-dependent multicolor upconversion emissions of Y2Mo4O15:Yb3+,Ho3+ for anti-counterfeiting and information encryption applications

A unique smart upconversion material Y2Mo4O15:40%Yb3+,2%Ho3+ that can respond to the power density and pulse width of the excitation light is developed.

Multicolor upconversion emission and highly optical temperature sensing based on lanthanide-doped double perovskite Sr2LaNbO6 phosphors

Here we adopt trivalent lanthanide (Ln3+ = Er3+, Er3+/Ho3+, and Yb3+/Tm3+) doped Sr2LaNbO6 (SLNO) as novel upconversion luminescence (UCL) materials for achieving UCL and optical temperature sensing under 980 nm excitation. Specifically, Er3+ single doped Sr2LaNbO6 phosphors present bright high-purity green emission under the 980 nm excitation. While co-doping with the Ho3+ ions, the component of red emission from Er3+ ions increases significantly and sample show a remarkable enhancement of luminescent intensity relative to SLNO:Er3+ sample. The above-mentioned phosphors and Yb3+/Tm3+ co-doped phosphor (blue emission) successfully achieve high-purity trichromatic UCL and mixed white light output in the same host. Furthermore, the temperature sensing performance of the SLNO:Er3+/Ho3+ phosphor based on the fluorescence intensity ratio (FIR) is systematically studied for the first time. The temperature sensing based on the non-thermal coupling levels (NTCLs) exhibit higher sensitivity than that based on the thermal coupling levels (TCLs). The maximum absolute and relative sensitivity for 4F9/2/4I9/2 NTCLs reach 0.16803 K−1 at 427 K and 0.01591 K−1 at 641 K, respectively. Interestingly, NIR emission of 4I9/2 → 4I15/2 transition presents a thermal enhancement, while visible emissions show thermal quenching. These results indicate that the Ln3+ doped Sr2LaNbO6 UCL phosphors have potential applications in the fields of non-contact temperature sensors, full-color displays, and anti-counterfeiting.

Wide multicolor tunability of blue-to-green up-conversion emission and white light generation in Pr3+/Yb3+ co-doped yttrium tantalates

We achieved wide multicolor tunable up-conversion emission and white light generation in Pr3+/Yb3+ co-doped yttrium tantalates prepared by a soft sol–gel method designed to afford the cubic Y3TaO7 and monoclinic M′-YTaO4 crystalline phases. The annealing temperature influenced the crystallization kinetics and stabilized a preferential phase. To investigate how the crystalline phase affected the Pr3+ photoluminescence properties, we recorded up-conversion emission spectra for the samples annealed at 900 or 1100 °C. Excitation at 980 nm elicited emissions assigned to the Pr3+ transitions in the blue (3P0→3H4), green (3P1,0→3H5), and red (3P0→3H6,3F2; 3P1→3F3) regions. The Yb3+ content, crystalline phase, and laser power influenced such emissions. The most dominant mechanisms are proposed to elucidate the differences in the number of photons during the power dependence studies. Spectroscopic studies showed that the crystalline structure composition and Yb3+ concentration affected the population of the Pr3+:3P1,0 states and modified the relative intensity of bands particularly in the green and red regions. These changes provided extensive color gamut, so we evaluated emission color tunability from blue to green as a function of the Yb3+ concentration. The above-mentioned structural and photoluminescent properties make these Pr3+/Yb3+ co-doped yttrium tantalates potential candidates for applications in Photonics, mainly in the integration of white, blue, or green LED systems, multicolor displays, and other devices for security applications.

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.

Concentration based multicolor upconversion emission of lanthanides Co-doped Ruddlesden-Popper type layered perovskites

Abstract Yb3+ ions initiated upconversion properties of Ruddlesden-Popper type layered materials were studied to elucidate the tunability of the visible emission under 980 nm excitation. The substitution of lanthanum ions in the host layer perovskites with different concentrations of Yb3+/Er3+ and Yb3+/Tm3+ as the sensitizer/activator pairs was performed via the solid-state procedure. The upconversion spectra of the samples have depicted that the materials relatively lower dopant concentrations of Yb3+/Er3+ have the green color, which was shifted to the red region due to both heavy activator and sensitizer concentrations because of the dominant 4F9/2 → 4I15/2 transition rather than the 2H11/2, 4S3/2 → 4I15/2 transitions. The tunability of upconversion emission of Yb3+/Tm3+ introduced materials was limited in the visible region compared to the Yb3+/Er3+ pair despite the fact that the wide variety of the lanthanide concentrations were studied and the layered materials were structured successfully. On the other hand, the first intense NIR emission was achieved for the layered perovskites co-doped with Yb3+/Tm3+ due to the 3H4→ 3H6 relaxation.

Multicolor upconversion emission of Ho3+ in single NaYF4 microrod

Lanthanide-doped upconversion nano/micro-materials exhibit superior and fascinating optical properties due to their unique 4f–4f transitions. They have been extensively investigated in various fields. Thus, studying the upconversion optical characteristic, especially for Er3+, Tm3+, and Ho3+ ions, is extremely important and useful. In this work, a strong upconversion emission with a candy-like fluorescent pattern has been discovered in a single NaYF4: Yb3+/Ho3+ microrod via confocal microscopy under NIR 980 nm excitation. When the Yb3+ ion-doped concentrations and the excitation power are increased, the Ho3+ ions show an increased blue emission intensity and high R/G ratio in single NaYF4 microrod, which is due to the cross-relaxation between Ho3+ ions. The corresponding upconversion emission behaviors and physical mechanisms have been studied on the basis of the spectral characteristics of Ho3+ ions and rate equations. Meanwhile, the candy-like emission pattern of single NaYF4 microrod is explained by establishing optical models, which because of the occurrence of fluorescence total reflection. The present study is of great importance in NaYF4 micro-materials doped with rare-earth ions, thereby providing new applications in optical anti-counterfeiting, 3D-displays, and wave-guides.

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.

Energy transfer and cross-relaxation induced multicolor upconversion emissions in Er3+/Tm3+/Yb3+ doped double perovskite La2ZnTiO6 phosphors

Investigation on the bright and stable upconversion (UC) phosphors with multicolor emissions is fundamental and significant for the frontier applications of display and temperature probe. Here, diverse emitting colors with blue, cyan and yellowish green, which are caused by the energy transfer and cross-relaxation processes, are obtained by altering Er3+, Tm3+ and Yb3+ concentrations in Er3+ singly, Er3+ - Tm3+ - Yb3+ co- and tri-doped double perovskite La2ZnTiO6 (LZT) phosphors synthesized by a simple solid-state reaction. In addition, excellent infrared emission at 801 nm located at “first biological window” is collected in Tm3+-Yb3+ co-doped phosphors. Meanwhile, the temperature sensing properties based on the thermally coupled levels (2H11/2/4S3/2) of Er3+ ions were analyzed from 298 to 573 K of LZT:0.15Er3+/0.10Yb3+ phosphor, demonstrating that the maximal sensitivity value is about 56 × 10−4 K−1 at 448 K. All these results imply that this kind of UC material has potential applications in display, bioimaging and optical device.

Characterization and multicolor upconversion emission properties of BaMoO4: Yb3+, Ln3+ (Ln = Tm, Ho, Tm/Ho) microcrystals

Hydrothermal process was employed to synthesize the Yb3+/Tm3+, Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+ doped BaMoO4 octahedron microcrystals (0.50–5.0 µm). The synthesized phosphors have scheelite tetragonal structure. The elemental mapping suggests the uniform distribution of elements in the samples. The oxidation state of samples were investigated by X-ray photoelectron spectroscopy (XPS) which indicates the existence of Ba2+, Mo6+, O, Yb3+, Tm3+ and Ho3+ in samples. The presence of rare earth ions was also verified by observation of specific absorption peaks in diffuse reflectance spectra (DRS). The tunable multicolor upconversion (UC) emissions were successfully obtained under 980 nm NIR excitation by precisely adjusting the concentration of rare earth ions. The as prepared sample exhibits blue, green and red emission as a result of energy transfer from the Yb3+ to Tm3+ and Ho3+ ions. The power dependent UC emission spectra show the two photonic processes. The energy transfer mechanism from Yb3+ to Tm3+ and Ho3+ was explained via an energy level analysis.

The preparation and up-conversion properties of full spectrum CsPbX3 (X = Cl, Br, I) quantum dot glasses.

All-inorganic perovskite (CsPbX3) quantum dots (QDs) have achieved unprecedented success in various applications due to their outstanding performance. Nevertheless, the inherent instability of these QDs severely limits their practical applications. Here, ultra-stable full visible spectrum CsPbX3 (X = Cl, Br, I) QD glasses are prepared successfully. For the first time, the full spectrum tunable up-conversion (UC) emission of CsPbX3 QD glasses ranging from 420 nm to 711 nm under excitation with an 800 nm femtosecond (fs) laser was achieved. Importantly, the two-photon absorption properties, the exciton binding energy and the UC full width at half maximum (FWHM) of CsPbCl1.5Br1.5 (blue), CsPbBr3 (green), and CsPbBr1.5I1.5 (red) QD glasses were studied in depth. Furthermore, CsPbCl1.5Br1.5 showed the highest exciton binding energy (∼87.5 meV), allowing the CsPbCl1.5Br1.5 QD glass to act as a good optical gain material that could more easily achieve amplified spontaneous emission (ASE).

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...

3D printing of resin composites doped with upconversion nanoparticles for anti-counterfeiting and temperature detection.

Rapid prototyping (RP) techniques allow the construction of complex and sophisticated physical models based on personal needs, and the applications of the produced objects can be greatly extended by functionalizing the raw materials (e.g., resins) with components showing electrical, optical and magnetic properties. Here, we demonstrate a simple method for the realization of a three-dimensional architecture through 3D printing of organic resin doped with inorganic upconversion (UC) nanoparticles by using stereolithography technique. In our process, the wet-chemistry derived NaYF4: RE (RE: rare earth) nanoparticles with red, green and blue UC emission were incorporated into a resin matrix. We printed out pre-designed 3D structures with high precision and examined the UC emission properties. In a proof-of-concept experiment, we demonstrate that the 3D printed objects have reliable optical anti-counterfeiting based on high concealment in daylight and multi-color UC emission excited by a near-infrared laser at 980 nm. We also show that the 3D part with UC emission can be used for ratiometric temperature sensing from 303.15 K to 463.15 K, making it possible to map the temperature distribution for studying the thermal diffusion process in complex objects.

Promising light converting BaMoO4:Er3+-Tm3+-Yb3+ phosphors for display and optical temperature sensing

Er3+-Tm3+-Yb3+ tri-doped BaMoO4 phosphors were synthesized by co-precipitation technique and characterized by X-ray diffraction analysis, absorption study and field emission scanning electron microscopy analysis. Upconversion as well as downconversion luminescence studies were performed by using near infrared (980 nm) and ultraviolet (380 nm) excitations. Energy level diagram, pump power dependence and colour coordinate study were utilized to describe the multicolor upconversion emission properties. Under single 980 nm diode laser excitation the dual mode sensing behaviour is realized via Stark sublevels and thermally coupled energy levels of the Tm3+ and Er3+ ions in the prepared tri-doped phosphors. A comparative fluorescence intensity ratio analysis for integrated emission intensities arising from the Stark sublevels {1G4(a) and 1G4(b)} and thermally coupled energy levels {2H11/2 and 4S3/2} of the Tm3+ and Er3+ ions, respectively was carried out in the prepared tri-doped BaMoO4 phosphors. The maximum sensitivity for thermally coupled energy levels of the Er3+ and Stark sublevels of the Tm3+ ion was reported. The developed phosphors could be useful in the display devices and optical thermometric applications.

Highly efficient multi-colour upconversion emission of Yb3+/Er3+, Ho3+ codoped single LiYF4 octahedral microparticle

In this work, Yb3+/Er3+, Ho3+ codoped tetragonal-phase LiYF4 octahedral microparticles have been successfully synthesized through a facile hydrothermal method. Here, we implemented a confocal microscopy setup to manipulate and study the optical properties of a single LiYF4 microparticle under a focused NIR 980nm excitation. The strong multi-colour upconversion emission intensity with beautiful luminescent patterns have been clearly observed. And output colours (the different ratio of red-to-green emission intensity) of single LiYF4: Yb3+/Er3+, Ho3+ microparticles have been anticipated to be adjusted by controlling Yb3+ doping concentrations. The results show that the different ratio of red-to-green emission intensity of Er3+ and Ho3+ in single LiYF4 microparticle, which is due to the cross-relaxation processes and energy back transfer processes between Yb3+ ions and Er3+ or Ho3+ leading to different population densities of intermediate energy levels. The upconversion emission mechanisms and the influence of Yb3+ concentrations on upconversion emission properties of Er3+ and Ho3+ ions are also discussed according to the emission spectra and rate equations.

Orthogonal Multiplexed Luminescence Encoding with Near‐Infrared Rechargeable Upconverting Persistent Luminescence Composites

AbstractThe orthogonal luminescence encoding technique is developed for the first time based on a novel near‐infrared (NIR) rechargeable upconverting persistent luminescence (UCPL) composites. The orthogonal encoding signals with multicolor upconversion emission and long persistent phosphorescence can be activated and work independently in the presence and absence of 980 nm excitation. The orthogonal encoding technique allows for a marked increase in the coding capacity compared with conventional luminescence encoding strategies. This strategy can offer a greatly increased coding capacity with less naked‐eye certifiable colors to decrease the decoding error rate induced by the chromatic aberration of the similar colors, which can be effectively decoded by the portable charge‐coupled device. In addition, the obtained NIR rechargeable UCPL materials show great potential applications for anticounterfeiting, rewriteable data encryption and decryption, zero‐background bioimaging, and noninvasive photo‐biostimulation, etc.