Upconversion Emission Research Articles

A bright Ce-based downshifting luminescence nanoprobe for NIR-IIb vessel imaging

Nanomaterials with unique emission in the second near-infrared window (NIR-II, 1000–1700 nm) are regarded as the promising probes for visualization of tumor vessels and cerebrovascular architecture, because of their superior features such as deep tissue penetration and large imaging resolution. Herein, the new Ce-based fluoride nanoparticles (NPs) with high-efficiency NIR-IIb emission were explored for high-resolution vascular imaging and tumor associated vessel detection. Under the same synthesis conditions, the Ce-based fluoride present the preferential formation CeF3 host and low upconversion (UC) emission, but possess more strong (1.45 times) NIR-IIb downconversion (DC) emission centered at 1525 nm under the irradiation of a 980 nm laser, which is significantly different from the traditional NaYF4:Yb/Er host. Through the efficient cross relaxation between Ce3+ and Er3+, intense NIR-IIb luminescence from Er3+ with high quantum yields were achieved, which make sure the entire mouse body and brain blood vessel imaging with supernal resolution (47.6 μm) were demonstrated. Moreover, the optical imaging in NIR-IIb region guided tumorous vascular visualization was successfully achieved. Therefore, the explored CeF3 NPs with boosting NIR-IIb emission can be employed as new diagnostic bio-probes used in high spatial resolution tumorous vessel detection.

Tailoring upconversion fluorescence of lanthanide doped nanocrystals by coupling to single microcavity mode with specific symmetry

Lanthanide-doped upconversion nanoparticles have unique optical properties that can absorb low-energy infrared photons and then emit higher-energy visible ones, which have been widely used for advanced optical sensors and fluorescent probes. Efficiently tailoring the upconversion emission is desirable for meeting the wavelength requirement in various application fields. However, up to now, optimizing the composition combining with core/shell structure is still the predominant way to reach this goal. Here, we show that the relative intensities of the emission peaks of upconverting nanoparticles can be tuned by coupling to single microcavity mode with specific symmetry. Theoretical calculation based on the finite-difference time-domain (FDTD) indicates that the symmetries of the microcavity modes dominate their resonant absorption properties in the visible region. As a result, the upconversion emission peaks vary in these microcavities with different symmetries. This route can be developed for tailoring the emission spectra of other luminescent materials, such as quantum dots and fluorescent dyes.

Near UV photon upconversion in cast solid with quantum dot

Abstract CdS/ZnS core-shell semiconductor quantum dots (QDs) were hybridized with1-naphthalenecarboxylic acid, a triplet transmitter, by a ligand exchange method. UV emission peaked at 340 nm or longer was obtained by visible continuous-wave excitation at 405 nm in n-hexane solution by mixing the hybridized QD with 2,5-diphenyloxazole (PPO) as UV emitter, based on triplet-triplet annihilation upconversion (TTA-UC) mechanism. The same mixture but in tetrahydrofuran gave solid film by solution casting, and the solid showed upconversion emission in near UV spectral region (380-395 nm) by 405-nm excitation.

Synthesis of Up-Conversion CaTiO3: Er3+ Films on Titanium by Anodization and Hydrothermal Method for Biomedical Applications.

The present study investigates the effects of Er3+ doping content on the microstructure and up-conversion emission properties of CaTiO3: Er3+ phosphors as a potential material in biomedical applications. The CaTiO3: x%Er3+ (x = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0%) films were synthesized on Ti substrates by a hydrothermal reaction at 200 °C for 24 h. The SEM image showed the formation of cubic nanorod CaTiO3: Er3+ films with a mean edge size value of (1-5) μm. When excited with 980 nm light, the CaTiO3: Er3+ films emitted a strong green band and a weak red band of Er3+ ions located at 543, 661, and 740 nm. The CaTiO3: Er3+ film exhibited excellent surface hydrophilicity with a contact angle of ~zero and good biocompatibility against baby hamster kidney (BHK) cells. CaTiO3: Er3+ films emerge as promising materials for different applications in the biomedical field.

Photocatalytic activity of Ho3+-Yb3+ activated BiVO4 upconverting phosphors

The BiVO4:Ho3+-Yb3+ upconverting phosphors have been synthesized by using the chemical co-precipitation method and optimized with 0.7 % Ho3+ + 6 % Yb3+ combination through frequency upconversion emission study. The synthesized phosphors have been characterized through XRD (X-Ray diffraction), FESEM (Field emission scanning electron microscopy), HR-TEM (High resolution- Transmission electron microscopy), UV–vis diffuse reflectance spectroscopy (DRS), Raman, and FT-IR (Fourier transform infrared spectroscopy). The XPS (X-ray photoelectron spectroscopy) analysis has been performed to study the elemental composition, chemical, and electronic states of the atoms present in the optimized sample. The specific surface area of the pure and optimized phosphors has been determined through BET (Brunauer-Emmett-Teller) analysis. From the XRD analysis, it is clear that on doping, the crystal structure of BiVO4 changes from monoclinic to tetragonal structure. The values of rate constants for the photocatalytic performance of the upconverting codoped and pure BiVO4 phosphors under the illumination with an artificial solar lamp for degradation of MB dye are found to be 0.00498 min−1 and 0.00269 min−1, respectively. To verify these results, the same experiment has also been performed under the visible LED (Light-emitting diode) light illumination. This enhancement of ∼ 85 % in the rate constant of the photocatalytic performance ensured the utilization of the NIR portion of the light by the codoped BiVO4 phosphors through the frequency upconversion process. The material’s recycling photocatalysis experiment for three cycles has been performed to check its reusability. The upconversion emission and XRD analysis of the materials after photocatalysis have been performed. From this study, it is confirmed that the stability of the sample is better even after three cycles of photocatalytic dye degradation experiment.

Natural and polyanionic heparin polysaccharide functionalized upconversion nanoparticles for highly sensitive and selective ratiometric detection of pesticide

Pesticide contamination is a global concern, threatening human health and food safety. Herein, we developed heparin (HEP) functionalized upconversion nanoparticles (UCNPs)-based ratiometric nanosensor for the sensitive detection of 2,6-dichloro-4-nitroaniline (DCN) pesticide via inner filter effect. The strategy for HEP functionalization of UCNPs is based on adjusting the surface potentials of UCNPs with polyanionic HEP through the electrostatic interaction. UCNPs (NaYbF4:Gd/Y/Tm@NaYbF4@NaYF4) was designed with core-shell-shell structure and extra sensitizer layer for efficient and strong upconversion luminescence (UCL) in the range of UV to NIR. After incorporation of DCN, the upconverted UV emission of UCNPs-HEP ratiometric nanosensor was considerably quenched with the NIR UCL at 800 nm remaining unchanged as internal standard. The UCNPs-HEP ratiometric nanosensor can achieve outstandingly selective and sensitive detection of DCN at the wide linear range of 5–300 μM with a detection limit of 0.41 μM. The remarkable applicability of the UCNPs-HEP ratiometric nanosensor was verified in apple, cucumber and grapes samples. The developed UCNPs-HEP ratiometric nanosensor with excellent biocompatibility and water dispersion capability, is promising for convenient, selective and sensitive sensing of DCN towards food and aqueous samples.

Construction of NaYF4:Yb,Er,Tb@NaYF4:Yb,Tb/NH2-MIL-88B(Fe) composite photocatalyst for effective photocatalytic degradation of antibiotics

Photocatalysis is an efficient and robust strategy to degrade the pollutant in the aqueous environment. However, the decomposition of antibiotics is still a perplexing problem due to the outstanding stability. To fabricate the heterogeneous photocatalyst upconversion nanoparticle (UCNPs)/metal–organic framework (MOFs) with the broadened solar light absorption, especially for the near-infrared (NIR) light, is a feasible pathway to accomplish the above goal. The heterogeneous photocatalyst, NaYF4:Yb,Er,Tb@NaYF4:Yb,Tb/NH2-MIL-88B(Fe) (ErTb@YYbTb/NMB), is firstly synthesized, in which the shell is coated along with the doped energy trapping ions to improve the upconversion efficiency. Under the simulated solar light, the degradation efficiency of ErTb@YYbTb/NMB reaches 76% for sulfamethoxazole (SMZ), 75% for ofloxacin (OFL), and 78% for norfloxacin (NOR). To elucidate the influence of energy trapping ions and coated shell, a series of UCNPs, NaYF4:Yb,Er (Er), NaYF4:Yb,Er,Tb (ErTb), NaYF4:Yb,Er,Tb@NaYF4:Yb (ErTb@YYb), and NaYF4:Yb,Er,Tb@NaYF4 (ErTb@Y) are also synthesized to compare with ErTb@YYbTb. The excellent performance of ErTb@YYbTb/NMB is attributed to the cooperation of covering the widened light spectrum, the enhanced upconversion emission intensity, and the feasible electron-hole separation, which are confirmed by the corresponding measurements including photoelectrochemical measurements, free radical and hole trapping experiments, and pump power dependence of upconversion emission intensities. Incorporation of UCNPs and MOFs to form the heterogeneous photocatalyst is a promising pathway to reach the ideal degradation goal for antibiotics.

Harnessing bright upconversion luminescence from PEG-coated NaGdF4:Ho3+/Yb3+ nanoparticles for contrast enhancement in dual mode OCT imaging and optical temperature sensing

In this work, authors synthesized the Polyethylene Glycol (PEG) coated NaGdF4:Ho3+/Yb3+ nanoparticles using the thermal decomposition reaction route. Our primary objective was to comprehensively evaluate their suitability for augmenting image contrast, particularly within the intricate domain of Swept Source Optical Coherence Tomography (SSOCT) and photo-thermal Optical Coherence Tomography (PTOCT) imaging modalities. Our meticulous inquiry yielded the revelation of extraordinary upconversion emissions, which emanated from the distinct transitions of Ho3+ ions, most notably the 5F4(5S2)→ 5I8 and 5F5→ 5I8 transitions. These transitions manifested as strikingly vibrant green emissions, precisely at the 539 nm and 661 nm wavelengths. Furthermore, we investigated the underlying upconversion mechanism, delving deeply into the elucidation of decay times and the nanoparticles' ability to transform incident radiation into thermal energy. Impressively, these nanoparticles exhibited a noteworthy photo-thermal conversion efficiency, specifically measured at an impressive 47.4 % along with the bright green luminescence. Our study also extended to bio-compatibility, where we achieved highly encouraging outcomes. Following 24 h of incubation with HeLa cells treated with UCNP-PEG, we ascertained a compelling cell survival rate exceeding 80 %, underscoring the favorable biocompatibility of these nanoparticles. Moreover, these nanoparticles demonstrated a conspicuous thermal sensitivity, quantified at 5.1 × 10−3 K−1 at 380K, thus signaling their potential for precision temperature monitoring and could be applied at the cellular level.

Enhancement of Vibrant Up-Conversion in (Ca,Sr)F2:Er,Yb,Al Phosphors via Energy Transfer, Localized Interstitial Distortion, and Au Nanostructures.

A remarkable increase in the luminescent intensity of Er3+-doped CaF2 up-conversion phosphors was achieved, showing an approximate enhancement of over 1100-fold. This enhancement was realized by incorporating Yb3+, Al3+, Sr2+, and gold nanospheres and nanorods. The substantial improvement in up-converting luminescence effectively enhances sensitivity and efficiency at low excitation power densities. The up-conversion phosphors, consisting of (Ca,Sr)F2:Er,Yb,Al, were easily prepared using excess NH4F flux at 950 °C for 30 min. The structural confirmation of interstitial Al3+ ions within the CaF2 lattice was achieved through synchrotron powder X-ray powder diffraction. The significant enhancement of up-conversion emission and their mechanisms in the phosphors were vividly represented through energy transfer, interstitials and local distortions, and localized surface plasmon resonances when excited with a 980 nm diode laser.

Upconversion of Infrared Light by Graphitic Microparticles Due to Photoinduced Structural Modification

Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. A model is offered, wherein the upconversion is facilitated by photoinduced electronic structure modification allowing for multiphoton processes. As per the prediction of the model, it is experimentally shown that graphite upconverts infrared light centered around 1.31 μm (0.95 eV) to broadband white light centered around 0.85 μm (1.46 eV). The results suggest that upconversion from shortwave infrared (≈3 μm, 0.45 eV) to visible region may be possible. The experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds.

Na5Y9F32:Yb3+/Ho3+/Tm3+ up-conversion luminescent single crystals for highly sensitive optical temperature sensor

A novel non-contact optical temperature sensor with excellent performance of its adequate temperature resolution (δ(T) = 0.017 K) and exceptional relative thermal sensitivity (Sr = 1.97% K−1) was developed based on the up-conversion fluorescence intensity ratio (FIR) of Ho3+/Tm3+/Yb3+ triply incorporated Na5Y9F32 single crystal grown by Bridgman method. The up-conversion (UC) emission bands at 482 nm/669 nm/700 nm of Tm3+ and 522 nm/542 nm/653 nm of Ho3+ ions were observed upon excitation of 980 nm. The effects of Yb3+ concentration from 0.5 to 4 mol% on the UC emission of the Ho3+/ Tm3+ fixed doped Na5Y9F32 single crystal were also carried out. It has been demonstrated through the calculation of the steady-state rate equation that the intensity of UC emission is linearly heightened with the pump power, confirming the conversion mechanism. The temperature sensing performance of the Ho3+/Tm3+/Yb3+ incorporated Na5Y9F32 single crystals was explored by analyzing the FIR employing thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs). The maximum values of absolute sensitivity (Sa) and relative sensitivity (Sr) of the material are estimated to be 19.1% K−1 (323 K) and 1.97% K−1 (398 K), separately, which are far higher than those of previously reported RE3+-doped UC optical temperature sensor materials. This study shows that the transparent single crystal has the great potential as a non-contact optical thermometer, and provides a new idea for studying other highly optical sensing materials.

The impact of high pressure on the number of photons involved in upconversion luminescence of NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles and application as contactless pressure sensor

Inorganic nanomaterials doped with lanthanide ions and exhibiting upconversion (UC) luminescence are leading in research of nonlinear optical materials. Extreme conditions, such as high-pressure compression (in the GPa range), may influence the physicochemical properties of various compounds. In this work, we investigated the optical properties of upconverting NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles (NPs), focusing on the impact of high pressure on the number of photons involved in the UC mechanism. We measured the UC emission spectra of the synthesized NPs under high-pressure conditions, which allowed us to observe the pressure-induced intensity changes, band centroids spectral shifts, and band intensity ratios alterations. Importantly, by measuring the power-dependent UC emission spectra as a function of pressure, we determined and analyzed the number of photons (n) involved in the UC processes for the first time. It turned out that the n value changes with pressure as a result of diverse multi-phonon relaxation processes enhanced under high-pressure conditions. The results show potential adjustment of UC mechanisms with the use of high-pressure. The calculated band intensity ratios were also used for pressure sensing applications, resulting in the relative sensitivity reaching almost ≈20 % GPa−1 for the Er3+-doped core@shell NPs.

Revelation of luminescence-thermometry, light generation in first biological window and IR detection capabilities of sodium yttrium fluoride co-doped with Yb3+ and Er3+ ions synthesized by low-cost approach

Microwave-assisted combustion synthesis approach is adopted to prepare sodium yttrium fluoride co-doped with ytterbium and erbium (NaYF4: Er3+/ Yb3+) nanoparticles. PXRD confirms the formation of mixed phase (cubic and hexagonal) of the NaYF4: Er3+/ Yb3+ crystal lattice. It is determined that the cubic phase dominates over the hexagonal phase. Three characteristic emission peaks appearing at 523, 544 and 672 nm are attributed to the transitions 2H11/2, 4S3/2 - 4I15/2 and 4F9/2 - 4I15/2 respectively which is character of Er3+ ions, confirming the potential in first biological window applications. The optimal dopant concentration is found and the asymmetric ratio is calculated. Strong up-conversion emission has been observed in the sample in the yellowish-green area when excited with 980 nm radiation. The life time of the 4S3/2 (green) and 4F9/2 (red) levels are found to be 1.187 and 0.472 ms respectively. The emission occurring in the synthesized sample follows the two-photon process which is confirmed by double log graph of intensity and pump-power. Thermal sensitivity is recorded in the range of 300–540 K. The thermally and non-thermally coupled levels attributed to the transitions (2H11/2 and 4S3/2) to (2H11/2 and 4F9/2) of Er3+ ions which are employed to study the temperature sensing. Higher relative sensitivities in both thermally and non-thermally coupled levels were observed in the samples with their values being 1.33 % K−1 and 1.81 % K−1 correspondingly. The significant thermal sensitivity of the synthesized phosphor materials improves its possibility in optical thermometric applications. Further to study the light-emitting abilities of the prepared phosphor, a phosphor-in-glass structure was fabricated using a borate-based glass system. The photometric parameters such as luminous efficacy of radiation and luminous efficiency were obtained to be 331 lm/Wopt and 48.46 % respectively. The prepared compound exhibits superior IR sensing which is evident upon exposure of the fabricated P-i-G to 980 nm radiation. The performed studies authenticate the capabilities of the cubic phase NYF in optical thermometry, light generation and IR detection abilities.

Novel protocol for rapid evaluation of plasmonic enhancement for up-converting phosphors applied to Y2O3 doped with Er3+ and Er3+/Yb3+

A novel technique was created to quickly evaluate the impact of various ratios on the efficiency of up-conversion emission using a combination of up-conversion nanophosphors (UCNPs) and gold nanoparticles (Au NPs). Four different types of Y2O3 UCNPs with different Er3+ or Er3+/Yb3+ doping, which affects the emission colour as well as the up-conversion mechanism, were prepared via the microwave-assisted hydrothermal method. Au NPs were produced independently using the reduction technique. Different ratios of UCNPs were mixed with the Au NPs in water. The mixed powder composites were extracted for analysis. X-ray powder diffraction was utilized to study the structure of UCNPs with and without Au NPs, while transmission electron microscopy was used to study the morphology and size of Au NPs. Absorption and up-conversion measurements were also made. The novel protocol allowed rapid evaluation of four different Y2O3 UCNPs of Er3+ and Er3+/Yb3+ doped with concentrations optimized for red and green emission over a range of Au/UCNP concentrations, which might usually be done in four separate studies. Despite the wide range of variables, only a decrease in UC emission was measured in the presence of Au NPs, suggesting that the conditions for plasmonic enhancement are limited and not easy to attain. In spite of this, in many phosphor/metal NP systems, the innovative prototyping process can enable quick assessment of possible plasmonic enhancement.

Huge enhancement in upconversion luminescence near-infrared emission of KYb (MoO4)2: Er3+ phosphor by doping Y3+ ions

The KYb(MoO4)2: Er3+, Y3+ phosphors were synthesized by high temperature solid state reaction method. By further doping Y3+ ions, the near-infrared (NIR, 804 nm, 4I9/2 → 4I15/2) luminescence of KYb(MoO4)2: 0.1 % Er3+ phosphor is greatly enhanced. Based on the upconversion luminescence (UCL) spectra, the optimal doping concentration of Y3+ ions were 7.5 %. Its near-infrared UCL intensity is about 26.9 times that of undoped Y3+ ions. Through a series of characterization methods, we find that the enhancement of NIR upconversion emission is due to the generation of defect bands. It plays a crucial role in facilitating the transfer of energy from green light level (2H11/2, 4S3/2) to red light level (4F9/2) and near-infrared level. To explain the luminescence mechanism, the power dependence, UV-VI-NIR absorption spectra, excitation spectra at 804 nm and emission spectra at 380 nm were studied. In addition, the 804 nm single near-infrared UCL intensity of KYb (MoO4)2: Er3+, Y3+ shows a linear variation with temperature in the temperature range of 298 K–673 K. The maximum sensitivity is 0.13 % K−1. This study provides a new method and theoretical support for the application of near-infrared UCL in optical temperature measurement.

Upconversion, downshifting, quantum cutting and back energy trasfer from Yb3+ to Er3+ in Er3+/Yb3+ co-doped CaTiO3 phosphor, intense NIR generation for communication

The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO3:0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO3:0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source.

Upconversion luminescence and temperature sensing in novel CaLa2ZnO5:Ho3+/Yb3+ phosphors

Phosphors of the ternary metal oxide CaLa2ZnO5 host co-activated with Ho3+/Yb3+ were synthesized using the solution combustion method. X-ray powder diffraction carried out the phase confirmation for different doping concentrations. Surface morphology and elemental composition were assessed through field emission scanning electron microscope images and an energy-dispersive X-ray spectrum. Using a 980 nm laser for excitation, the up-conversion (UC) emission spectra were recorded at 500–800 nm. Photoluminescence measurements for emission between 1100 and 1300 nm were also made for the same excitation. The UC emission spectra recorded between 500 and 800 nm consisted of green, red, and near-infrared emission peaks characteristic of Ho3+ ions. It was found that the variation in Yb3+ concentration significantly affected the UC emission through energy transfer. Power-dependent UC measurements were also carried out for the recorded emission spectra. The temperature sensing capability of the synthesized phosphors was investigated for the non-thermally coupled levels 5F4,5S2 → 5I8 and 5F5 → 5I8, using the fluorescence intensity ratio technique. The maximum values corresponding to the absolute and relative sensitivity were estimated to be 0.19 and 1.78 K−1, respectively. The synthesized phosphor was found to have good thermal stability up to 473 K with an activation energy of 0.73 eV. The synthesized phosphor can, therefore, be efficiently used as a probe for temperature sensing, especially at high temperatures.

Ag3PO4/PtNPs-NaYF4:Yb,Tm, an up-conversion photocatalyst for enhanced degradation efficiency of pollutants in water

For developing and utilizing near-infrared (NIR) energy in sunlight, NaYF4:Yb,Tm (NYFYT) up-conversion luminescent powder was combined with Ag3PO4 (AP) and Ag3PO4/Pt nanoparticles (AP/PtNPs) as a photocatalyst. Driven by NIR light, NYFYT produces up-conversion emission at 348, 364, 453 and 478 nm, effectively stimulating the photocatalytic degradation performance of AP and AP/PtNPs. Under xenon lamp irradiation, the apparent rate constants (k) for Ag3PO4/Pt nanoparticles-NaYF4:Yb,Tm (AP/PtNPs-NYFYT) in photocatalytic degradation of rhodamine B (Rh B) and phenol are 5.51 and 12.82 times higher than those of AP and 1.90 and 2.37 times higher than those of AP-NYFYT-50 wt%, respectively. In addition, under 980 nm laser irradiation, rate constants are 3.26 and 4.16 times higher than those of AP-NYFYT-50 wt%, respectively. These results indicate that the combination of NYFYT and AP expands the absorption range of the composite photocatalyst and facilitates the NIR-driven photocatalytic process. The introduction of PtNPs effectively prevents the electron-hole recombination and the reduction of Ag+, accelerating the redox reaction and promoting the photocatalytic activity and stability of AP.

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.

Upconversion emission and its color modulation of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials

Upconversion emission and its color modulation of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials