Red Upconversion Luminescence Research Articles

Background-free luminescent and chromatic assay for strong visual detection of creatinine.

Creatinine is an essential biomarker for the clinical diagnosis and treatment of renal insufficiency. Although fluorescent methods are powerful tools for creatinine detection, almost all reported fluorescent probes rely on short-wavelength excitation and a single fluorescent signal, making them susceptible to environmental and operational conditions. In this study, a near-infrared excited, highly sensitive, and multi-output signal sensing system was established using upconversion nanoparticles and 3,5-dinitrobenzoic acid (DNBA) for synergistic luminescent and colorimetric assay for strong visual detection of creatinine. DNBA undergoes a specific colorimetric reaction with creatinine, quenching the green upconversion luminescence (UCL) while leaving the red UCL unaffected, thus constructing the luminescent and colorimetric sensing modes for creatinine. The designed near-infrared excited sensing system eliminates auto-fluorescence with a multi-output signal, thereby enhancing the sensitivity and convenience of creatinine detection. Under optimal conditions, the detection limit in the colorimetric mode is 26nM, while the detection limit in the luminescent mode is 2nM. Moreover, a portable sensing platform is further developed, demonstrating sensitive sensing performance and paving a new way for point-of-care testing (POCT) of human body fluid biomarkers.

Dual–resonance enhancement and polarization control of upconversion luminescence of NaYF4:Yb,Er nanoparticles on 2D metal gratings

In this work, we report enhancement and polarization control of multi–color (green/red) upconversion luminescence (UCL) of lanthanide–doped (NaYF4:Yb,Er) nanoparticles by dual–resonance modes of surface plasmons (SP) on two–dimensional (2D) metal gratings in orthogonal directions. Investigations are performed for the SP resonance modes to be tuned, by adjusting the grating periods, to match any one or two of the green–UCL, red–UCL and excitation wavelengths. It is shown that, for the upconversion nanoparticles (UCNPs) on the 2D gratings with both of the dual resonance modes matching the green–/red–UCL or excitation wavelength, enhancements of the UCLs are roughly doubled, compared with their one–dimensional (1D) counterparts. And when the dual resonance modes match the green– or red–UCL and the excitation wavelength, enhancements of the UCLs are further greatly improved, in spite that the resonance modes for the excitation and emission light are in orthogonal directions. As the emitted UCL photons are largely coupled with the dual SP resonance modes, the radiated green– and red–UCL light can be distinguished by their linear polarization states in orthogonal directions. It is also indicated that polarization of the excitation light can influence the polarization of the UCL light when coupled with the SP resonance modes.

Strong red upconversion luminescence of Yb3+/Er3+ co-doped Bi2O3 phosphors for optical thermometry

Strong red upconversion luminescence of Yb3+/Er3+ co-doped Bi2O3 phosphors for optical thermometry

Strong red upconversion luminescence of NaYF4: Yb3+, Er3+ through Sc3+ ions doping for temperature sensing

Strong red upconversion luminescence of NaYF4: Yb3+, Er3+ through Sc3+ ions doping for temperature sensing

Regulating novel tunable green to red upconversion luminescence in Er3+/Yb3+ co-doped SrBi2Nb2O9 ferroelectric ceramic

A series of SrBi2-x-yNb2ErxYbyO9 (SBN) ferroelectric ceramics co-doped with Erbium and Ytterbium have been fabricated through solid-state approach, the formation of pure phase SrBi2Nb2O9 has been confirmed by XRD spectra corresponding to orthorhombic geometry having phase group A21am. The lattice parameters and volume of the unit cell increase with the content of Yb3+. SEM study revealed the randomly oriented plate-like structure of SBN having average particle sizes ranging from 0.9 μm to 2.23 μm. The FTIR characteristic bands are found at wavenumber 602 cm−1 and 812 cm−1. In Photoluminescence (PL) spectra, two green emission bands (524 nm and 549 nm) and one weak red band (660 nm) are acquired using a 488 nm excitation wavelength. The diffuse reflectance spectra (DRS) of ceramic compounds reveal that the values of band gap ranges from values 2.7–3.1eV. Two UCL bands are seen at wavelength 533 nm, and at wavelength 554 nm in the green part of the upconversion photoluminescence (UCL) spectra, and a single band observed at a wavelength of 672 nm in the red region upon excited by 980 nm laser. The green band dominates for initial concentration up to x = 0.03, y = 0.03 after which red emission dominates with increasing concentration of Yb3+. The dependence study of pump power on UCL emission intensity reveals that there are two photons are involved in UC emissions of green and red. The time decay analysis of SBN composition showed that the average decay time of Er3+ is 70μs and that of the co-doped system (Er3+/Yb3+) is 37 μs

Enhanced red upconversion luminescence induced by Yb-Fe dimer for bifunctional biological applications in optical thermometry and photothermics

Enhanced red upconversion luminescence induced by Yb-Fe dimer for bifunctional biological applications in optical thermometry and photothermics

Synthesis and characterizations of upconverting luminescent Er3+/ Yb3+: Gd2O3 uniform nanospheres for biomedical applications

We present the synthesis of Er3+/ Yb3+ co-doped Gd2O3 nanospheres using the wet-chemical method followed by a synergistic step-by-step calcination process, a novel approach in the field. The nanospheres exhibited red color upconversion luminescence (UCL) after multi-step annealing at temperatures ranging from 650 °C to 1150 °C, achieving a fully spherical morphology. The diameter and surface morphology of the nanospheres were significantly altered by the annealing process, decreasing from 382.77 ± 1.72 nm with a smooth surface to 245.7 ± 1.31 nm with a rougher surface. The UCL intensity increased with the annealing temperature. The influence of Er3+/ Yb3+ co-doped Gd2O3 nanospheres, excited by a 975 nm laser, was investigated, and the decay time for UCL samples was analyzed. The luminescence peak at 1026 nm was attributed to the 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+) transition/ or 2F5/2 → 2F7/2 of the Yb3+ ions within the Gd2O3 matrix. Furthermore, the UCL properties of Er3+/ Yb3+ co-doped Gd2O3 nanophosphors were explored to detect the NTERA-2 cancer cells. These findings suggest that the rare earth co-doped Gd2O3 nanospheres might hold significant potential for biomedicine and imaging diagnostics applications, sparking new interest and possibilities in these fields.

Preparation and significant enhancement of upconversion luminescence of α-Ba2ScAlO5:Yb3+/Er3+ phosphors by Ca2+ ions doping

The intensity of upconversion luminescence (UCL) poses a significant challenge for oxides characterized by high phonon energy. Herein, a significant enhancement of red UCL is achieved through the introduction of an intermediate band (IB) in α-Ba2ScAlO5: Yb3+/Er3+ by Ca2+ ions doping. The absorption spectra verify the existence of the IB. The IB of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+ increases the host's absorption of excited photons, provides more electrons for the excitation of Er3+, and realizes the enhancement of UCL emission. The optimal concentration of Ca2+ in α-Ba2ScAlO5: 0.2Yb3+, 0.03Er3+ is 0.15. Compared with undoped Ca2+ samples, the red and green UCL intensity of α-Ba2ScAlO5: Yb3+, Er3+, 0.15Ca2+ increased by 48.2 and 10.6 times, respectively. The mechanism of Ca2+ enhanced UCL was investigated by analyzing the UCL spectra, absorption spectra and lifetime decay curves of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+. The temperature-dependent UCL properties of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+ were also studied by the 2H11/2 (525 nm) and 4F9/2 (667 nm) energy level radiation transitions. The observed linear correlation between luminescence intensity and temperature, coupled with its high sensitivity, indicates the promising potential for temperature sensing applications. This study not only opens a new avenue for enhancing UCL but also holds significant implications for sparking widespread interest in non-contact temperature sensing applications leveraging UCL.

Multimodal anti-counterfeiting and optical storage application based on luminescence reversible modification and color change of photochromic phosphor

Reversible upconversion luminescence (RUCL) modification based on photochromism has received considerable interest due to its potential applications in optical storage and invisible optical anti-counterfeiting. Herein, white β-Ba2ScAlO5: Yb3+, Er3+ (β-BSAO-YE) phosphor was irradiated with 254 nm light, which caused the phosphor to turn blue due to the increase of oxygen vacancy. The blue β-BSAO-YE phosphor returns to its original color upon stimulation with 808 nm laser light or 125 °C, exhibiting a double photo-induced reversible photochromic change. The green and red upconversion luminescence (UCL) of the β-BSAO-YE were reversibly modified according to their photochromic properties. The UCL modification changes the luminescence color of the pattern, indicating that β-BSAO-YE phosphor is an ideal compound anti-counterfeit agent. The light information recorded on the β-BSAO-YE binary photochromic dot matrix can be read under ultraviolet (UV) and near-infrared (NIR) excitation, demonstrating the potential application of β-BSAO-YE phosphors as optical data storage media. In addition, the cyclic experiment showed good photochromic and UCL modulation repeatability. The new luminescent β-BSAO-YE not only proposes a new way to exploring upconversion red light materials, but also provides new materials for optical storage, optical information and optical anti-counterfeiting.

Strong red upconversion luminescence of Yb3+/Er3+ co-doped Sc6WO12 phosphor for optical thermometry

Herein, a strong red upconversion phosphor of Yb3+/Er3+ co-doped Sc6WO12 was prepared by employing an equivalent substitution approach. When irradiated by 980 nm near-infrared laser, the phosphor emits strong 660 nm red light. The main excitation mechanism for its red upconversion luminescence emission is the energy transfer process, through which the Er3+ ions is promoted from the 4I13/2 energy level to the 4F9/2 energy level. In addition, it is noteworthy that the multimode upconversion luminescence phosphor exhibits three different trends upon temperature change, and its upconversion emission integral intensity ratio exhibits a linear relationship with temperature in the range of 298 K–623 K. This special property makes the phosphor promising for applications in optical temperature measurement.

Modulated upconversion luminescence of water-dispersed NaErF4@NaYF4 nanoparticles by introducing Tm3+/Ho3+ as energy capture centers under multi-wavelength NIR excitation

Water-dispersed red upconversion nanoparticles (UCNPs) have great application prospects in the biomedical field. Thus, a series of Er3+-based upconversion nanoparticles (Er-UCNPs) with excellent red upconversion luminescence under three-wavelength NIR excitation (808/980/1550 nm) were prepared by a simple thermal decomposition method, and then further functionalized by PAA to achieve good water dispersibility. Compared with NaErF4 bare core, the emission intensity of Er-UCNPs samples doping of 0.5%Tm3+ and 0.5%Ho3+ as energy capture centers was significantly enhanced, and further improved after coating with NaYF4 inert shell. Meanwhile, among all Er-UCNPs@NaYF4 samples, NaErF4@NaYF4 exhibited the highest emission intensity and longest luminescence lifetime due to the efficient suppression of luminescence quenching effect, while NaErF4:0.5%Tm3+@NaYF4 showed highest red luminescence purity owing to the energy transfer process between Tm3+(3H5) and Er3+(4I13/2). The hydrophilic Er-UCNPs@NaYF4@PAA samples still maintained good red luminescence under multi-wavelength excitation. The luminescence enhancement mechanism in Er-UCNPs@NaYF4 was discussed in detail based on spectral characteristics. The as-prepared water-dispersed Er-UCNPs@NaYF4@PAA with bright red luminescence under multi-wavelength NIR excitation will have potential applications in targeted therapy and deep tissue imaging.

Improved thermometry sensitivity of red-emitting SrGd2O4:Er3+,Yb3+ phosphors using novel NTCL-FIR technology based on 2H11/2 and 4F9/2

In this work, the upconversion luminescence (UCL) and temperature-sensing properties of SrGd2O4 phosphors doped with Er3+, Yb3+ were investigated. The UCL performance was studied by adjusting the doping concentrations of Er3+, Yb3+. It can be found that the intensity of red UCL is effectively improved by doping Yb3+ ions. The band structures of SrGd2O4, SrGd2O4:5 mol%Er3+, and SrGd2O4:5 mol%Er3+,15 mol%Yb3+ were calculated using the density functional theory (DFT) to verify the experimental results. The thermal sensitivity of SrGd2O4:5 mol%Er3+,15 mol%Yb3+ phosphors was studied using the novel fluorescence intensity ratio of non-thermally coupled energy levels (NTCL-FIR) technique based on the 2H11/2 and 4F9/2 energy levels. The analytical results reveal that the maximum values of Sr are 1.69%/K (300 K), 1.18%/K (300 K) and 1.47%/K (300 K) respectively under 915, 980 and 1550 nm excitations. The Sr values of novel NTCL-FIR are compared with that of thermal coupling of energy level (TCL) and other studies in the same field. The results show that the thermometry sensitivity of red-emitting UCL materials can be enhanced by using the novel NTCL-FIR technique. In addition, the intense red UCL of SrGd2O4:Er3+,Yb3+ phosphors have the advantage of deeply penetrating biological tissues. Therefore, the combination of novel NTCL-FIR and red-emitting SrGd2O4:Er3+,Yb3+ phosphors could be conducive to temperature monitoring in vivo.

Investigation of the sensitization effect of Yb3+ in Yb, Er co-doped Sr5(PO4)3F transparent ceramics: From single-band red upconversion to temperature sensing behavior

Lanthanide-ion-doped red upconversion (UC) fluorescent materials with excellent signal-to-noise ratio, stability, and red-green luminous intensity ratio have proven of tremendous research importance for biomedical, three-dimensional (3D) displays, sensors, and other sectors. In this study, xYb, 1Er: Sr5(PO4)3F (S-FAP) (x=0–5 at%) transparent ceramics with outstanding optical quality were fabricated by hot pressing the co-precipitation powder with high sintering activity. The energy dispersive X-ray (EDX) results showed that the trivalent lanthanide ions were evenly doped into the S-FAP ceramic lattice. Increased Yb3+ doping considerably restricted the growth of ceramic grain size, which should be attributable to a decrease in sintering activity under high Yb doping conditions. The co-doping of Yb3+ successfully resulted in a significant improvement in up/down conversion efficiency via effective energy transfer mechanisms and the optimization of the electron population at the energy level of red-green emission. Furthermore, single-band red upconversion luminescence with the greatest red-green upconversion luminescence integral intensity ratio of 125.74 was discovered under 980 nm laser pumping at room temperature. The energy transition process involved in the phenomenon of the up-conversion luminescence intensity shift of red-green emission has been thoroughly examined. Finally, the noncontact optical thermometric ability based on fluorescence intensity ratio (FIR) technology showed that the maximum absolute sensitivity (Sa) of the 5Yb1Er sample in the temperature range of 320–556 K is 1.1×10−3 K−1, implying the possible use of Yb/Er-doped S-FAP transparent ceramics in the field of optical thermometers.

Upconversion luminescence through dynamically regulating the depletion of Ho3+: 5I6 level for speed sensing

In this work, a strategy for dynamically adjusting the upconversion luminescence (UCL) color of NaGdF4:Yb3+/Ho3+/Ce3+/Sc3+ is reported based on a phosphor wheel. It has been demonstrated that the rotation-dependent UCL mainly originated from the regulation of depletion mode for the Ho3+: 5I6 level. Due to the dominant linear decay, a high-pure red UCL is observed under the steady-state excitation. However, as the proportion of the steady-state excitation decreases, the green–red emission intensity ratio gradually increases, followed by the color conversion from red to green. An approximate physical model is proposed to understand the dependence of IG/IR on rotation speed. We not only report a UCL material that shows potential application in velocity sensing but also provide new insights into wheel-based dynamic UCL regulation.

Large enhancement of red upconversion luminescence in beta Ba2Sc0.67Yb0.3Er0.03AlO5 phosphor via Mn2+ ions doping for thermometry

Here, this study reports single-band red upconversion emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor by doping Mn2+. The optimum concentration of Mn2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ phosphor was 0.20. The intensity of red and green emissions is increased by 27.4 and 19.3 times, respectively. Compared with the samples without Mn2+ ions, the red-green integral strength ratio of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ sample was significantly increased by 28.4 times, reaching 110.9. The UCL mechanism was explored by analyzing the down-conversion luminescence spectra, absorption spectra, UCL spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Mn2+ co-doped β-Ba2ScAlO5. The enhancement of upconversion red light is achieved through energy transfer between defect bands and Er3+ ions, as well as energy transfer between Mn2+ ions and Er3+ ions. In addition, the Mn2+ doped β-Ba2ScAlO5: Yb3+/Er3+ red UCL phosphors have great potential for ambient temperature sensing in the 298–523 K temperature range. The maximum sensitivity of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ phosphor as a temperature sensor at 523 K is 0.0247 K−1.

Quantitative Fluorescent Lateral Flow Strip Sensor for Myocardial Infarction Using Purity-Color Upconversion Nanoparticles.

Acute myocardial infarction is a serious cardiovascular disease and poses significant risks to human health. Its early diagnosis and real-time detection are of great importance. Herein, we design a low-cost device that has a high sensitivity of cTnT and cTnI detection. Dual-color upconversion nanoparticles (UCNPs) are prepared as probes, which not only have high-purity red upconversion luminescence (UCL) under 980 or 808 nm excitation but also achieve good temperature sensing. Temperature-dependent multicolor emission excitation is obtained, and the color turns from white to orange and red with increasing temperature. In particular, the maximum SR and SA values based on nonthermally coupled levels are 4.76% K-1 and 8.6% K-1, which are higher than those based on thermally coupled levels. With the UCNPs-based lateral flow strip (LFS), the specific detection of cTnI and cTnT antigens in samples is achieved with a detection limit of 0.001 ng/mL, which is 1 order of magnitude lower than that of their clinical cutoff. The UCNPs-LFS device has a low-cost laser diode and a simplified laser and permits a mobile-phone camera to collect the results, which has an important influence on the field of biomarker sensing.

Exploring energy mechanisms involved in the luminescence reduction due to Ce3+ doping via core-multishell upconversion nanoparticles highly doped with Ho3+ and Yb3+

Upconversion nanoparticles (UCNPs), particularly those that are highly doped, possess outstanding properties and have demonstrated tremendous application potential. However, novel fine-tuning strategies are urgently required to enhance the upconversion luminescence (UCL) performance of UCNPs. In this study, a series of core–multishell UCNPs highly doped with Ho3+ and Yb3+ ions were synthesized via the oleate route. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and UCL spectra and decay times, and pump power dependency of the synthesized UCNPs were used to examine their morphology, size, and the UCL properties. Ce3+ ions were introduced to enhance Ho3+-based red UCL, and their doping strategy was also optimized based on summarized UCL trends and detailed UCL mechanism analysis. NaHoF4:Gd3+@NaGdF4:Yb3+,Ce3+@NaGdF4:Yb3+ UCNPs that had 10 mol% Ce3+ dopants in their middle shells exhibited better UCL properties than the larger traditional NaGdF4:Yb3+,Ce3+,Ho3+ UCNPs, probably because of the combined influence of the energy interactions between the Ce3+ ions and surface groups, sensitizing energy enhancement by active shells, and the positive cooperation between the Ce3+ ions and highly-doped core–shell structures. In this study, the phenomenon of UCL decrease resulting from Ce3+ ion doping was explored. Using unique core–multishell structures with highly-doped activators and sensitizers placed within and outside the structures, respectively, the UCL decrease due to Ce3+ ion doping was attributed to a competition for photons. Doping the UCNPs with Ce3+ ions near the UCNP surfaces favors Ho3+-based red UCL. Our study findings can deepen the understanding of the Ho3+-based UCL mechanisms and increase the potential uses of NaHoF4 materials in photo-induced therapy.

Achieving Orthogonal Upconversion Luminescence of a Single Lanthanide Ion in Crystals for Optical Encryption.

Optical encryption shows great potential in meeting the growing demand for advanced anti-counterfeiting in the information age. The development of upconversion luminescence (UCL) materials capable of emitting different colors of light in response to different external stimuli holds great promise in this field. However, the effective realization of multicolor UCL materials usually requires complex structural designs. In this work, orthogonal UCL is achieved in crystals with a simple structure simply by introducing modulator Tm3+ ions to control the photon transition processes between different energy levels of activator Er3+ ions. The obtained crystals emit red and green UCL when excited by 980nm and 808nm lasers, respectively. The orthogonal excitation-emission properties of crystals are shown to be very suitable for high-level optical encryption, which is important for information security and anti-counterfeiting. This work provides an effective strategy for obtaining orthogonal UCL in simple structural materials, which will encourage researchers to further explore novel orthogonal UCL materials and their applications, and has important implications for the development of the frontier photonic upconversion fields.

High quenching concentration of the CaLuAlO4:Er3+ upconversion phosphor with short-range energy migration

Low activator concentration in upconversion phosphors has been a hindrance in improving luminescence performance. Herein, we report an Er3+ doping concentration as high as 30 at. % in the CaLuAlO4 upconversion host. The CaLuAlO4:Er3+ phosphors were prepared by the traditional high-temperature solid-state method. Under the excitation of a 980 nm laser, the optimal concentration of Er3+ approaches 30% according to the total integrated intensity of red and green upconversion luminescence. This quenching concentration is one order of magnitude higher than that in the traditional Er3+ doped upconversion polycrystals. The results obtained from first-principles calculations suggest that there are no in-plane or chain rare-earth ions in the cell. This increases the difficulty of propagating excitation energy to quench centers and is advantageous for high doping concentration. Our work can spark people's interest in the research and application of highly doped upconversion phosphors.

Rapid detection of microalgae cells based on upconversion nanoprobes.

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.