Blue Upconversion Emission Research Articles

Multi-mode up-conversion emission of Tm@Yb@Er phosphors for color modulation and thermometry

Rare earth doped up-conversion materials play an important role in information security, colorful display and temperature sensing. In this work, the up-conversion luminescence of NaYF4:0.2Tm/20Yb@NaYF4:20Yb@NaYF4:2Er/20Yb phosphors, synthesized by typical co-precipitation method, are investigated under different excitation condition. The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm because the Tm3+ ions in the core cannot be excited by 1550 nm laser. More interesting, the value of red-to-green (R/G) and blue-to-green (B/G) can be finely manipulated by tuning the excitation pulse width and frequency. This phenomenon can be interpreted by different rising processes of the green, red and blue up-conversion emission. In addition, the core-shell structured sample displays a temperature-dependent color change, ranging from blue-green to purple. The green emissions, radiated from thermal coupled levels (2H11/24S3/2), are used in thermometry and the max relatively sensing sensitivity reaches 0.01 K−1 at 303 K. The findings indicate that the core-shell Tm@Yb@Er phosphors, with excitation-dependent and temperature-dependent up-conversion luminescence, have potential applications in information security and temperature sensing.

PEG-coated NaYF4:Tm3+/Yb3+ upconversion nanoparticles for OCT image contrast enhancer, optical thermometry, and security applications

Polyethylene glycol (PEG) coated NaYF4:Tm3+/Yb3+ upconversion nanoparticles (UCNPs) were synthesized, and their usefulness in improving image contrast in Swept source optical coherence tomography (SS-OCT) and photo-thermal (PT-OCT) imaging was assessed. Synthesized UCNPs have shown biocompatibility with a cell survival rate of more than 90% after 24 h of incubation of HeLa cells. Prepared particles have shown intense blue upconversion emission along with a photo-thermal conversion efficiency of 30.4%. Leveraging these UCNPs, enhancements in image quality were achieved in both SS-OCT and PT-OCT imaging modalities, manifesting improved scattering coefficients and contrast-to-noise ratios. Temperature-dependent upconversion emission spectra were used to assess temperature sensing and thermal sensitivity of 107×10-3 K-1 at 300 K is obtained for the synthesized nanoparticles. Additionally, these UCNPs have demonstrated utility in latent finger-marks detection and anti-counterfeiting applications.

Constructing micro/nano-photonics barcodes based on micro-region upconversion emission spectrum of single core-shell microcrystal

The construction of core-shell structures with different structural properties based on the epitaxial growth technique has become an effective technique for regulating the luminescence properties of micro/nanocrystals. In order to obtain richer spectral information, NaYF<sub>4</sub>:50%Yb<sup>3+</sup>/2%Tm<sup>3+</sup>@NaYF<sub>4</sub>@NaYF<sub>4</sub>:20%Yb<sup>3+</sup>/2%Er<sup>3+</sup>@NaYF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> multilayered core-shell microcrystals are prepared by using multiple epitaxial growth through introducing surface modifiers and controlling their reaction conditions. The XRD and SEM results clearly show that the core-shell microcrystals possess a pure hexagonal crystal structure in the form of a disk. The microdesk has a thickness of about 2.32 μm and a diameter of about 28.31 μm. The upconversion luminescence characteristics of different single microcrystal structures are investigated by a confocal microspectroscopy system. In order to realize the selective excitation and emission of a single microcrystal, the spatial distribution of luminescent ions can be controlled through introducing an intermediate isolation layer. Under 980 nm laser excitation, different excitation sites of the single microdisk exhibit different upconversion emission characteristics. The significant blue (450 and 475 nm), red (648 nm) and green (524 and 540 nm) emissions are observed, which mainly originat from Tm<sup>3+</sup> and Er<sup>3+</sup> radiative transitions. Meanwhile, the red and blue upconversion emission intensities of the microcrystals are improved by using various shell layers. In addition, the luminescence and energy-transfer features of single microcrystals are explored by changing the excitation position. The experimental results demonstrate that the incorporation of NaYF<sub>4</sub> inert shells between luminescent layers can regulate luminescence and prevent ions from interacting. By utilizing the spectral fingerprint data of dopant ions in various shell layers, we create customizable micro-nano photonic barcodes and employ them for optical anti-counterfeiting detection. This study explores the use of constructed core-shell structures with luminescent tunable micron core-shell structures to acquire diverse spectral information and maintain stability through their structural properties. Thus, this core-shell structure provides a novel method for using upconversion luminescent microcrystals into micro- and nanophotonics to achieve anti-counterfeiting and display purposes.

Self-ratiometric fluorescent platform based on upconversion nanoparticles for on-site detection of chlorpyrifos

Monitoring organophosphorus pesticides is significant for food safety assessment. Herein, we developed upconversion nanoparticles (UCNPs)-based self-ratiometric fluorescent platform for the detection of chlorpyrifos. The UCNPs have the ability to confine the detection and reference functions in one nanoparticle. Specifically, the blue upconversion (UC) emission (448 nm) in the shell layer of UCNPs is quenched by the product of the acetylcholinesterase-mediated reaction, while the red UC emission (652 nm) from the core remains constant as a self-calibrated reference signal. Employing the inhibition property of chlorpyrifos, self-proportional fluorescence is employed to detect chlorpyrifos. As proof-of-concept, test strips are fabricated by loading the UCNPs onto filter paper. Combined with the smartphone and image-processing algorithm, chlorpyrifos quantitative testing is achieved with a detection limit of 14.4843 ng mL−1. This portable platform displays anti-interference capability and high stability in the complicated matrix, making it an effective candidate for on-site application.

Achieving thermochromic upconversion of Tm3+ for high-sensitive nanoprobe and information encryption

Upconversion-based optical thermometry has many merits, such as quick temperature response, higher thermal sensitivity and robust reliability. However, the previous works were mainly focused on the thermally coupled emissions, limiting their thermal sensitivity due to the intrinsic constraint by small energy gaps (e.g., <2000 cm−1) according to Boltzmann distribution theory. Here, we report a design of NaYF4:Yb3+/Tm3+@NaYF4 core-shell nanostructure to achieve thermochromic upconversion and high thermal sensitivity by taking advantage of nonthermally coupled upconversion emissions of Tm3+. We show that the blue upconversion emission of Tm3+ at 475 nm (1G4→3H6) exhibits a regular decrease with elevating temperature, while its deep-red emission at 696 nm (3F2,3→3H6) presents an increase. Such a feature leads to a rapid rise of luminescence intensity ratio (I696 nm/I475 nm) and the optimal relative sensitivity (Sr) reaches 2.79 % K−1 (503 K). More interestingly, the sample gives rise to a gradual emission color change from blue to purplish-red with lifting temperature. Our results offer a new class of upconversion-based nonoprobe with high thermal sensitivity and observable emission color variation, showing a great potential for nanoprobe and information security.

1.76 μm on-chip gain characteristics of Tm3+ in a rib waveguide based on Tm3+-doped LiNbO3 thin-film on insulator

A theoretical study has been performed on 1.76 μm on-chip amplification characteristics of Tm3+ in a rib waveguide of LiNbO3 on insulator (Tm:LNOI) under 795 nm wavelength pumping. Steady-state rate equations and propagation equations of signal and pump waves are established on the basis of a three-level model of Tm3+ system with the cross relaxation process 3H4→3F4: 3H6→3F4 included. The validity of the three-level model is demonstrated by referencing previously reported experiment result of Er3+-doped LNOI waveguide amplifier and by examining the effect of Tm3+ blue upconversion emissions on the 1.76 μm amplification. Besides the relations of signal gain to propagation length, launched pump power and input signal power, the effects of waveguide cross-section geometry and Tm3+ concentration on the gain characteristics are also studied. The results show that the waveguide cross-section geometry affects definitely the gain performance via its effect on mode field. The Tm3+ concentration affects the signal gain also via its effect on the 3H4→3F4: 3H6→3F4 cross relaxation coefficient, besides the conventional effect that higher active ion concentration yields larger signal gain. A comparison with conventional Ti4+(Zn2+)-diffused Tm3+-doped LN [Ti(Zn):Tm:LN] waveguide shows that the Tm:LNOI waveguide has much better gain performance than the Ti(Zn):Tm:LN waveguide, including much stronger pump power and propagation distance dependences of signal gain, much higher signal gain and much lower threshold pump power. These features are associated with significantly increased Tm3+ population inversion extent due to ultra-compact mode field and larger overlapping factor of mode field and Tm3+ population profiles in the Tm:LNOI waveguide.

Optimization of blue upconverted light emission based on fluoroindate glass matrix and subsequent chitosan functionalization.

Lanthanide-activated upconversion (UC) materials are fascinating for the new generation of biomedicine, because its unique ability to transform near-infrared light into visible light. Based on it, a set of fluoroindate glass matrices co-doped with Yb3+ and Tm3+ were prepared using the melting quenching technique. Then, the sample with the highest blue upconverted emission was milled and functionalized with chitosan (CS). The blue UC emission spectra of the glass increase with increasing Yb3+ concentration up to 1.8 mol%, then decreased. This could be attributed to the mechanism involved in the UC process, as confirmed by power dependence assessment. Also, according with the decay times the energy transfer efficacy of the samples is ∼50%. The milling of the glass resulted in particles of 44.8 ± 7.7 nm, which were successfully functionalized with CS. The CS-coated particles showed good cell viability, indicating that they could potentially be used in some biomedical applications.

Crystal growth and infrared-to-visible upconversion luminescence in Nd-Yb-Tm: CaYAlO4 single crystal

Yb3+/Tm3+: CaYAlO4 (CYA) and Nd3+/Yb3+/Tm3+: CYA bulk single crystals were grown using the Czochralski (Cz) method. The polarized absorption, upconversion luminescence (UCL) spectra under 980 nm and 808 nm pumping, and fluorescence decay curves were measured as well as Judd-Ofelt (J-O) theory calculations were performed to investigate the sensitization effect of Yb3+ and Nd3+/Yb3+co-doping in Tm3+: CYA single crystal. Obvious enhancement was observed in Tm3+-activated crystals for the blue upconversion emission (∼474 nm) when doped with Yb3+ or co-doped with Nd3+/Yb3+. The energy transfer efficiency is 72.6% (Yb3+→Tm3+) and 71.7% (Nd3+→Yb3+/Tm3+) in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA single crystals respectively. The gain cross-sections were calculated, and it can stated that the blue laser output derived from upconversion is possible around 474 nm related to the transition of 1G4→ 3H6 in Yb3+/Tm3+: CYA and Nd3+/Yb3+/Tm3+: CYA crystals.

Stable and low-threshold photon upconversion in nondegassed water by organic crystals.

Photon upconversion (UC) is a technology that converts lower-energy photons (longer wavelength light) into higher-energy photons (shorter wavelength light), the opposite of fluorescence. Thus, UC is expected to open a vast domain of photonic applications that are not otherwise possible. Recently, UC by triplet-triplet annihilation (TTA) between organic molecules has been studied because of its applicability to low-intensity light, although the majority of such studies have focused on liquid samples in the form of organic solvent solutions. To broaden the range of applications, solid-state UC materials have been an active area of research. We recently developed air-stable, high-performance molecular UC crystals that utilize a stable solid-solution phase of bicomponent organic crystals. This article begins with a brief overview of previous challenges in developing and improving solid-state TTA-UC materials. Then, we briefly review and explain the concept as well as advantages of our molecular solid-solution UC crystals. We applied these organic crystals for the first time to a water environment. We observed blue UC emission upon photoexcitation at 542nm (green-yellow light) and then measured the excitation intensity dependence as well as the temporal stability of the UC emission in air-saturated water. In nondegassed water, these organic crystals were stable, functioned with a low excitation threshold intensity of a few milliwatts per square centimeter, and exhibited high photo-irradiation durability at least over 40h; indicating that the developed organic crystals are also viable for aqueous conditions. Therefore, the organic crystals presented in this report are expected to extend the domain of UC-based photonic applications in practical water systems including in vivo diagnostic, clinical, and therapeutic applications.

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.

The Effect of a Yb Co-Dopant on the Blue Upconversion and Thermoluminescent Emission of SrLaAlO4:Yb3+,Tm3+ Phosphors

In this study, we described the structural, morphological, optical, photoluminescence, and thermoluminescence properties of SrLaAlO4:Tm3+,Yb3+ (SLAO:Tm,Yb) blue-emitting phosphors made by combustion synthesis and a post-annealing treatment at 1200 °C. The Yb co-dopant concentration was varied (1.0, 3.0, 5.0, and 6.0 mol%) while the Tm dopant concentration was fixed at 5 mol%. According to the X-ray diffraction patterns, all the samples presented the pure tetragonal phase of SrLaAlO4. Scanning electron microscopy analysis showed that the SLAO powders had morphologies of irregular or bar grains with average sizes in the range of 0.5–1.07 µm. Photoluminescence emission under 980 nm excitation showed an intense blue emission peak at 481 nm. The phosphors also emitted red light at 654 nm and a prominent NIR emission at 801 nm. All those emissions correspond to 1G4 → 3H6, 1G4 → 3H4 and 3H4 → 3H6 transitions of Tm3+. The SLAO:Tm,Yb phosphors synthesized with 3.0 mol.% of the Yb co-dopant showed the highest emission intensity in the visible/near-infrared (NIR) range (400–800 nm), and its CIE coordinates corresponded to the blue color (0.19368, 0.15826). Additionally, thermoluminescence emissions were recorded for the SLAO:Tm,Yb phosphors. The samples were previously irradiated with UV wavelengths of 265 nm, 365 nm, and 385 nm prior to the thermoluminescent measurements. After this, the kinetic parameters such as frequency factors, activation energy (E), and order of kinetics were calculated using the Chen method. The thermoluminiscent emissions demonstrated that the SLAO:Yb,Tm phosphors can be used for UV dosimetry.

Near-infrared laser-irradiated upconversion nanoparticles with dexamethasone precise released for alleviating lung ischemia-reperfusion injury.

Introduction: Dexamethasone (DEX), as an important enduring-effect glucocorticoid (GC), holds great promise in the field of lung ischemia-reperfusion injury (LIRI) comprehensive therapy owing to its immunomodulatory properties, such as inducing apoptosis and cell cycle distribution. However, its potent anti-inflammatory application is still restricted because of multiple internal physiologic barriers. Methods: Herein, we developed upconversion nanoparticles (UCNPs) coated with photosensitizer/capping agent/fluorescent probe-modified mesoporous silica (UCNPs@mSiO2[DEX]-Py/β-CD/FITC, USDPFs) for precise DEX release synergistic LIRI comprehensive therapy. The UCNPs were designed by covering an inert YOF:Yb shell on the YOF:Yb, Tm core to achieve high-intensity blue and red upconversion emission upon Near-Infrared (NIR) laser irradiation. Results: Under suitable compatibility conditions, the molecular structure of photosensitizer can be damaged along with capping agent shedding, which endowed USDPFs with an outstanding capability to carry out DEX release controlling and fluorescent indicator targeting. Furthermore, the hybrid encapsulating of DEX significantly increased utilization of nano-drugs, improving the water solubility and bioavailability, which was conducive to developing the anti-inflammatory performance of USDPFs in the complex clinical environment. Discussion: The response-controlled release of DEX in the intrapulmonary microenvironment can reduce normal cell damage, which can effectively avoid the side effects of nano-drugs in anti-inflammatory application. Meanwhile, the multi-wavelength of UCNPs endowed nano-drugs with the fluorescence emission imaging capacity in an intrapulmonary microenvironment, providing precise guidance for LIRI.

Glass-based composites comprised of CaWO4:Yb3+, Tm3+ crystals and SrAl2O4:Eu2+, Dy3+ phosphors for green afterglow after NIR charging

In this paper, we demonstrated the fabrication of new phosphate-based composites with green persistent luminescence after being charged with near-infrared light using the direct doping method. The composites are composed of a phosphate glass and phosphors. The 75NaPO3 − 25CaF2 and 90NaPO3 − 10NaF (in mol%) were the 2 glasses of investigation. The intense blue up-conversion emission between 450 and 500 nm upon 980 nm pumping is obtained by adding CaWO4: Tm3+, Yb3+ crystals in the glass melt before quenching whereas the green persistent luminescence is from the SrAl2O4:Eu2+,Dy3+ phosphors also added in the glass melt. The green persistent luminescence above 0.3 mcd/m2 is observed for ∼30 min after charging with 980 nm due to energy transfer between the upconverter crystals and the persistent luminescent phosphors. Here, the challenges related to the fabrication of such composites are discussed. While it is important for the blue UC emission to be intense to charge the SrAl2O4:Eu2+,Dy3+ crystals, we demonstrate that the glass matrix should not crystallize upon the addition of the different crystals. Additionally, the composites should remain translucent with limited light scattering for the blue UC emission to charge the persistent luminescent phosphors.

Tm3+; Yb3+:Zn2TiO4 near infrared to blue upconversion phosphors for anti-counterfeit applications.

Tm3+; Yb3+:Zn2TiO4 samples have been synthesized using a solid state reaction route. The phase, lattice parameters, crystallite size has been examined using X-ray Diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). An intense peak of Yb3+ codoped samples is observed near ∼957 nm due to the 2F7/2 → 2F5/2 transition in diffuse reflectance spectra (DRS), which confirms the presence of Yb3+ ion in the prepared compound. The optical band gap of Yb3+ codoped samples has been calculated using Kubelka-Munk function. The Raman spectra corresponds to incorporation of Tm3+/Yb3+ at the octahedral and tetrahedral site of the spinel host. The emission spectra recorded by using 370 nm excitation wavelength shows intense blue colour band corresponding to the 1G4 → 3H6 transition of Tm3+ ion. The upconversion (UC) emission spectra recorded by using 980 nm laser excitation source shows emission bands due to the 1G4 → 3H6, 1G4 → 3F4 and 3H4 → 3H6 transitions of Tm3+ ion in the host matrix lying in the blue, red and NIR regions respectively. There is effective enhancement of about ∼35 times in the blue UC emission intensity with incorporation of Yb3+ at 3% doping concentration in the prepared sample. The anti-counterfeit application of the optimized upconverting phosphor has been successfully demonstrated.

Blue frequency upconversion emission and optical thermometry of Ca3(PO4)2: Tm3+/Yb3+

Rhombohedral phase Ca3(PO4)2: Tm3+/Yb3+ phosphor is synthesized via hydrothermal route, and then frequency upconversion emission is studied upon 980 nm excitation. The samples have resulted strong blue emission around 472 nm and two weak emission bands at 650 and 700 nm wavelengths. The blue emission was optimized by changing the Yb3+ ion concentration, and optimum emission is observed for the sample having 0.5 mol% Tm3+ and 5 mol% Yb3+. The temperature-dependent upconversion luminescence studies were done under 980 nm excitation. The Judd–Ofelt intensity parameters were calculated using the absorption spectra and found in Ω2 > Ω4 > Ω6 order. Further temperature sensitivity of sample is explored by considering 1G4 and 3F2,3 levels as non-thermally coupled. Maximum absolute sensor sensitivity is found to be 3.63 × 10−3 K−1 at 623 K. The results indicate that Ca3(PO4)2 host is suitable for achieving intense blue upconversion emission and may be helpful for biological imaging considering the biocompatibility nature of Ca3(PO4)2.

Intense blue-emitting Yb/Tm-CaSiO3 wollastonite upconversion phosphors

Wollastonite is a naturally occurring mineral with a chemical formula of CaSiO3. Owing to outstanding mechanical, chemical, and thermal stabilities, wollastonites have become one of the most versatile industry minerals for applications in construction materials, cement, plastics, paints and coatings, friction, automobile brakes, ceramic and metallurgical applications to name a few. Despite technological importance, research on functional properties such as photon upconversion in wollastonites is still lacking. In this report, an initiative has been taken to demonstrate ultra-violet, blue, and near-infrared photon upconversion in CaSiO3 wollastonite via Yb and Tm doping. The wollastonite ceramics are synthesized via microwave hydrothermal technique followed up by heat-treatment in air. β-wollastonite (2M) phase in the synthesized samples has been confirmed by X-ray diffraction and a successful doping of Yb3+ and Tm3+ ions in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The most intense phonon band has been observed at 872 cm−1. Upon 980 nm excitation, ultraviolet, intense blue, and near-infrared upconversion emissions as well as downshifting infrared emissions are observed from Tm3+ ions as a result of sensitization by Yb3+. The temporal evolution of the emitting states is studied to understand the emission mechanism. An absolute upconversion quantum yield of the 20Yb/0.5Tm–CaSiO3 sample in the 400–850 nm range is 0.79%.

Near-infrared rechargeable glass-based composites for green persistent luminescence

The fabrication of Yb3+, Tm3+ co-doped oxyfluorophosphate glass-based composites, with green persistent luminescence after being charged with near-infrared light, is demonstrated. The mechanism responsible for the green afterglow after near-infrared illumination is unveiled. The composite is prepared using a modified melting process to limit the evaporation of fluorine during melting. Intense (blue and ultraviolet) up-conversion emission is obtained by optimizing the Yb2O3 and Tm2O3 concentrations. A heat treatment promotes volume precipitation of Yb3+, Tm3+ co-doped CaF2 crystals. Although the intensity of the blue up-conversion emission from the Tm3+1G4 level is lower in the highly Yb3+-concentrated glass-ceramic due to reverse energy transfer from Tm3+ to Yb3+, the heat treatment leads to an increase of the intensity of the emissions around 346 nm, 361 nm nm and 450 nm coming from the Tm3+1I6 and 1D2 levels. By combining the Yb3+ and Tm3+ ions with SrAl2O4:Eu2+,Dy3+crystals, green afterglow can be obtained after charging with near-infrared light.

Intense green photoluminescence and upconversion-based intrinsic optical bistability in Ho3+/Yb3+ codoped CaSc2O4 and upconversion in Ho3+/Yb3+ codoped CaY2O4 phosphors

The present study details the downshifting, frequency upconversion and intrinsic optical bistability in CaSc2O4:Ho3+/Yb3+ and upconversion in CaY2O4:Ho3+/Yb3+ phosphors synthesized by a complex-based precursor solution method. The X-ray powder diffraction confirms the formation of highly crystalline phosphors with pure orthorhombic phase. Fourier transform infrared studies of synthesized phosphors show vibrational bands due to the presence of Ca–O, Sc–O and Y–O groups. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to presence of Ho3+ and Yb3+ ions. The values of optical band gap (Eg) are found to be 5.69 eV and 5.58 eV for the Ho3+/Yb3+ codoped CaSc2O4 and CaY2O4 phosphors, respectively. The Ho3+/Yb3+ codoped CaSc2O4 phosphors display intense green downshifting emission upon 454 nm excitations. The lifetime of green luminescence of CaSc2O4:Ho3+/Yb3+ phosphors with varied Yb3+ concentrations have also been measured. The decay curves show a non-exponential nature fitted to the Inokuti-Hirayama model and the energy transfer microscopic parameters have been also calculated. The Ho3+/Yb3+ co-doped CaSc2O4 and CaY2O4 phosphors display intense green alongwith weak blue, red, and near-infrared upconversion (UC) emissions upon 980 nm excitations. The spectral color purity (Sgr) of CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor is calculated to be 0.78. Importantly, the variation of pump power generates intrinsic optical bistability (IOB) in the CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor for the green emission, which is not observed in the CaY2O4:Ho3+(1%)/Yb3+(5%) phosphor. Therefore, the Ho3+/Yb3+ co-doped CaSc2O4 phosphor could potentially be used in UC-based devices, optical memory devices, optical gates, optical transistors and switching devices for optical communications.

A single-beam NIR laser-triggered full-color upconversion tuning of a Er/Tm:CsYb2F7@glass photothermal nanocomposite for optical security.

The development of advanced luminescent materials is highly desirable for addressing the rising threat of forgery. However, it is challenging to achieve stable full-color upconversion (UC) tuning in the same matrix upon a single-beam light excitation so as to ensure that authentic items are irreproducible. Herein, hexagonal Er/Tm:CsYb2F7 nanocrystals (NCs) embedded inorganic glass via an in situ crystallization strategy is fabricated, which can emit blue, cyan, green, yellow, orange, red and near-infrared (NIR) UC emissions by simply modifying an incident 980 nm laser power. This UC tuning is attributed to the combination roles of the highly efficient laser-induced photothermal effect of the CsYb2F7 host and simultaneous emissions of Er and Tm activators. Importantly, the robust inorganic glass matrix endows Er/Tm:CsYb2F7 NCs with excellent water resistance and the ability to withstand high-power laser irradiation. Based on these unique characteristics, a proof-of-concept anti-counterfeiting experiment is designed. The results indicate that dynamic full-color UC luminescence patterns can be easily tuned by simply changing the power of the incident 980 nm laser. The present work not only confirms that the designed photothermal material can increase information security, but also provides a new idea for practical applications in the field of anti-counterfeiting.

The upconversion luminescence from visible to near-infrared in pyrosilicate C-Er2Si2O7

Rare earth pyrosilicate C-Er2Si2O7 ceramics were synthesized by the conventional solid-state reaction method. We observed strong photoluminescence (PL) peaks of Er3+ around 1546 nm with a lifetime of 135.4 μs at room temperature, which is longer than that of Er2Si2O7 films fabricated on Si substrate. Under 980 nm excitation, obvious blue, green, and red upconversion (UC) emissions of Er3+ are observed in this material, making C-Er2Si2O7 a potential material for color display. The luminescence mechanism that two and three photons participate in the energy level excitation was analyzed. Moreover, the near-infrared UC emission in the first biological window was also observed in C-Er2Si2O7, indicating that this material can be used in the in vivo field.