Upconversion Luminescence Intensity Research Articles

Improved upconversion luminescence of NaBiF4: Tm3+/Yb3+/Al3+ as a ratio thermometer

NaBiF4: 0.5 %Tm3+/20 %Yb3+/x%Al3+ upconversion luminescence materials were synthesized by co-precipitation method. The crystal structure, upconversion luminescence properties and temperature measurement properties systematically studied. Under 980 nm laser excitation, the characteristic transitions of Tm3+ were observed, corresponding to 1G4 → 3H6 (475 nm), 1G4 → 3F4 (650 nm), 3F2, 3 → 3H6 (700 nm) and 3H4 → 3H6 (800 nm), respectively. Al3+ substitution significantly increases the upconversion luminescence intensity, and the fluorescence lifetime of 1G4 level shortens from 277.8 to 179.1 μs. An anomalous thermal enhancement behavior is observed. The optical thermometry properties of Tm3+ based on the non-thermally coupled energy levels 3F2, 3 and 3H4 have been studied using the fluorescence intensity ratio technique. Relative sensitivity and absolute sensitivity show maximum values at 316 K, which are 1.1 % K−1 and 0.21 % K−1, respectively. The above results demonstrate that this material is a promising optical ratio thermometer.

Luminescence performance, temperature sensing characteristics and Judd-Ofelt theory analysis of Y2MoO6:Er3+/Yb3+/Li+ upconversion phosphors

A series of Y2MoO6:0.01Er3+/0.09Yb3+ upconversion phosphors doped with different concentrations of Li+ ions (0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 mol) were prepared by the high temperature solid phase reaction method, and their physical phase structures and upconversion luminescence were analyzed. At the excitation wavelength of 980 nm, the addition of Li+ sharply increased the upconversion luminescence intensity. With the increase of Li+ ion content, the luminescence intensity first increases and then decreases. When the doping amount reaches 0.25 mol, the luminescence intensity reaches the maximum, and the sample emits green light in the two-photon process. Y2MoO6:0.01Er3+/0.09Yb3+/0.25Li+ exhibits excellent temperature sensing properties. Its absolute sensitivity Sa reaches up to 0.012 K-1, the relative sensitivity Sr is 0.017 K-1 and the measurement error δT is less than 0.3 K at room temperature. Its temperature sensing performance is far superior to similar materials. In addition, Judd-Ofelt theory calculations revealed that in comparison with Y2MoO6:0.01Er3+/0.09Yb3+, its Ω2 increased from 0.56×10-20 cm2 to 3.68×10-20 cm2 , and the spectroscopic quality factor Ω4/Ω6 ratio reached 4.09, which is much higher than that of the other fluorescent materials. The main reason is that Li+ replaces the Y3+ ion lattice site, causing lattice distortion and reducing the lattice symmetry around the active ion. The increase in asymmetry increases the possibility of spontaneous radiative transitions. It is shown that the prepared upconversion luminescent materials have potential applications in the field of solid-state lasers and optical sensing.

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.

Enhancing upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+/Mo4+ by doping Sc3+ or Sb

AbstractBased on the previous optimal concentration of Er3+/Yb3+/Mo4+ co‐doped BiTa7O19 (BTO) samples, Sc3+ or Sb is planned to be doped into BTO:Er3+/Yb3+/Mo4+ for further improving the upconversion luminescence (UCL) intensity under 980‐nm laser excitation. A series of BTO:Er3+/Yb3+/Mo4+/Sc3+ and BTO:Er3+/Yb3+/Mo4+/Sb samples are prepared by high‐temperature solid‐phase sintering method. The microstructure and UCL properties are investigated by X‐ray diffraction, Raman, X‐ray photoelectron spectroscopy (XPS), diffuse reflection, and luminescence spectrum. The green UCL intensity of BTO:Er3+/Yb3+/Mo4+/Sb is little better than that of BTO:Er3+/Yb3+/Mo4+/Sc3+, which reaches 2.40 times than that of β‐NaYF4:Er3+/Yb3+. XPS results show that Sc is 3+, Mo is 4+, and Sb is 3+ and 5+. Raman spectra show that BTO:Er3+/Yb3+/Mo4+/Sb has lower phonon energy and more disorder than BTO:Er3+/Yb3+/Mo4+/Sc3+. The maximum relative temperature sensitivity is got as 0.01012 K−1 at 303 K based on luminescence intensity ratio technology. BTO:Er3+/Yb3+/Mo4+/Sb has outstanding pure green UCL intensity, which can be applied to luminescence display and temperature sensing.

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.

Microwave assisted preparation of ternary scheelite CaMoO4: Er3+/Yb3+ nano-phosphors for up/down-conversion photoluminescence, temperature sensing and antibacterial properties

Due to their exceptional intrinsic optical characteristics, molybdate compounds have aroused significant attention in recent years for their effective up and downconversion luminescence. In the present study, a series of xEr3+/Yb3+ (x = 0.5 %, 1 %, 2 %, 4 % and Yb3+ =15 %) doped CaMoO4 nanophosphors synthesized through a microwave assisted approach and subsequently the comprehensive analysis of the functionalities such as optical properties, antibacterial traits and their integration with temperature sensing, have been explored. Furthermore, the structural refinement confirms the occurrence of tetragonal scheelite phase of the prepared materials. The morphology of the material was identified by FE-SEM and HR-TEM analysis which reveals particles are in spherical shape. Up-conversion luminescence intensities were found to be dependent on doping concentration, laser excitation power and external temperature upon 980 nm light excitation. The temperature sensing response of the optimized sample was examined based on intensity ratio of two emission bands that involves thermally connected energy levels of Er3+ ion. The maximum absolute sensitivity of 10.74 × 10−3 K−1 (at 500 K) was found, demonstrating its potential application in high temperature thermometry. The comprehensive analysis and the outcome of the present study suggests the potential prospect of the as-synthesized material in food preservation, medical equipment, water treatment, and as an optical coating agent for solid state luminous devices.

A novel single near-infrared luminescence of negative thermal quenching materials for optical temperature measurement

In recent years, upconversion (UC) luminescence has gained attention due to its unique optical properties, and the thermal response spectral characteristics of these materials have been widely utilized in various fields including temperature sensing and biomedical research. However, the photoluminescence (PL) intensity of most rare earth ions doped phosphors decreases with increasing temperature, and the visible fluorescence emission penetration is still limited. In the work, the pure phase of Yb3+ and Er3+ ions co-doped Sc2Mo3O12 was successfully prepared. The Sc2Mo3O12: Yb3+, Er3+ sample showed a single emission of UC near-infrared (NIR) light. The optimum doping concentrations of 0.2 for Yb3+ ions and 0.01 for Er3+ ions were achieved. The possible upconversion luminescence (UCL) mechanism was investigated by analysing the UCL spectra, the down-shift (DS) excitation and emission spectra of Sc2Mo3O12: Yb3+, Er3+ phosphor. The excitation path of NIR emission is mainly through Er3+ from 2H11/2 to 4I9/2 energy level. What's more, the temperature-dependent near-infrared UCL properties of sample is explored in the temperature range from 323 K to 673 K. The enhancement of upconversion luminescence intensity shows a linear relationship with increasing temperature. The study paves a new way for non-contact optical temperature measurement with single near-infrared UCL emission.

Enhancement of upconversion luminescence and temperature sensing performance in Er3+/Yb3+ doped Lu2O3 and Lu2O2S phosphors by incorporation of lithium ions

A series of spherical Er3+/Yb3+ doped Lu2O3 and Lu2O2S phosphors co-doping with varying concentrations of Li+ (0, 1, 3, 5, and 7 mol%) were synthesized by homogeneous precipitation method followed by direct calcination or sulfurization. The crystal structure and morphology of the as-prepared phosphors were characterized by XRD, FTIR and SEM. Meanwhile, the upconversion (UC) luminescence spectra were recorded under 980 nm laser excitation at temperatures ranging from 303 to 573 K. The incorporation of lithium ions led to an enhancement of UC luminescence intensity by about 15 times at room temperature. The introduction of Li+ could also affect the temperature sensitivity of the samples. Furthermore, optical temperature sensing of the phosphors was achieved by analyzing the fluorescence intensity ratio (FIR) of thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs). Impressively, utilizing the non-TCLs approach resulted in maximum Sa values of 8.80 %K−1 and 11.06 %K−1 for the Er3+/Yb3+/5 % Li+ doped Lu2O3 and Lu2O2S phosphors, leading to an approximately 17-fold and 23-fold increase compared to that of TCLs-based approach, respectively. The results of this work demonstrate the great potential of Er3+/Yb3+/Li+ doped Lu2O3 and Lu2O2S phosphors for optical thermometers.

Up-conversion luminescence and thermal sensing properties of LuYO3: Er3+/Yb3+ phosphor

A series of LuYO3: Er3+/Yb3+ phosphors with different Yb3+ concentrations were prepared through a melting zone method with CO2 laser. The samples emit bright up-conversion luminescence (UCL) under a 980 nm laser. The UCL intensity and the luminescence color change significantly when Yb3+ concentration changes. Besides, when doped with 3 mol% Yb3+, the UCL intensity is maximal. The thermal sensing properties of LuYO3: Er3+(0.5 mol%)/Yb3+(3 mol%) were studied using the fluorescence intensity ratio (FIR) method from 298 K to 848 K. The maximum absolute and relative sensitivities are 0.0050 K−1 at 366 K and 0.0167 K−1 at 298 K, respectively. Thus, the LuYO3: Er3+(0.5 mol%)/Yb3+(3 mol%) fluorescent material is very suitable for thermal sensing because of the wide temperature range and the high sensitivity.

Graphene quantum dot-functionalized upconversion nanoparticles for highly sensitive detection of food contaminant azodicarbonamide

Excessive consumption of flour products containing excessive azodicarbonamide (ADA) has been associated with some adverse effects in humans. Thus, developing a facile method to monitor the amount of ADA in flour is extremely significant. Herein, a graphene quantum dot (GQD) sensitized upconversion nanoparticles (GQD-UCNPs) was designed to monitor the amount of ADA in flour with high specificity and sensitivity. Surface coating of UCNPs with GQD by coordination interaction significantly enhances the upconversion luminescence (UCL) intensity and the water solubility of UCNPs. Copper ions (Cu2+) can quench the UCL intensity of GQD-UCNPs through electron transfer processes. After introduction of glutathione (GSH), the UCL intensity of GQD-UCNPs gradually increases because of the interaction between GSH and Cu2+, accompanied by the generation of Cu+. The sulfydryl group of GSH can be oxidized to disulfide bond by ADA, which hinders the interaction between GSH and Cu2+, preventing the recovery of UCL intensity. Thus, the presence of ADA decreases the UCL intensity of GQD-UCNPs + Cu2+ + GSH system, allowing for the quantitative detection of ADA. The nanosensor realized a highly sensitive and specific ADA detection with a high detection limit down to 0.055 μM. Furthermore, excellent recovery rates in spiked real samples were obtained, indicating that the designed method possesses good prospects for practical application. Notably, this method broadens the application prospects of upconversion technology in the field of food safety.

Outstanding blue upconversion luminescence and thermal enhancement behavior in BiTa7O19:Tm3+/Yb3+ phosphors

Extremely intense blue upconversion luminescence (UCL) is got in Tm3+/Yb3+ co-doped BiTa7O19 (BTO) phosphors, which are synthesized by solid phase sintering. The doping concentration of Tm3+ is fixed at 7 mol%, and the concentration of Yb3+ is adjusted. When the concentration of Yb3+ is 80 mol%, the strongest blue UCL can be obtained under 980 nm laser excitation. The blue UCL integral intensity under 808 + 980 nm laser co-excitation is 1.54 times of the sum of intensity under 808 and 980 nm single excitation, respectively. Blue UCL thermal enhancement behavior was found for all the samples under 808 or 785 nm laser excitation, and blue UCL thermal quenching happened under 660, 660 + 808, and 359 nm excitations. It is demonstrated that UCL thermal enhancement behavior is caused by oxygen defects. The possible electron transition pathways are proposed under excitation with different laser wavelengths. Using the luminescence intensity branching ratio (LIR) technique, the maximum relative temperature sensitivity range is calculated to be from 0.00610 to 0.00732 K−1 at 303 K. The experimental results show that BTO:Tm3+/Yb3+ has excellent blue UCL with thermal enhancement, which can have some applications in the field of UCL display and temperature sensing in high temperature environment.

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.

Significantly enhanced upconversion luminescence intensity and tailorable chromaticity of Sn4+-doped NaYF4:Yb3+/Er3+

The internal modification with rare earth ion doping proved to be a very effective strategy for improving the luminescent properties of NaYF4-based upconversion materials. However, greatly enhancing the luminescence efficiency of NaYF4:Yb3+/Er3+ remains a major challenge. Herein, the effects of Sn4+ doping on the structure and luminescent performance of such material were explored. The hydrothermal molten-salt method was applied to synthesize the Sn4+-doped NaYF4:Yb3+/Er3+ upconversion materials, and their crystal structures, morphologies, surface chemical composition and element states, and luminescence performance were characterized. It was found that Sn4+ doping can significantly enhance the luminescence intensity and tailor the chromaticity of NaYF4:Yb3+/Er3+. In particular, the green (G) and red (R) luminescence intensity levels of the 30 mol% Sn4+ doped material were increased by factors of 26.97 and 38.91, respectively. The R/G ratio was incremented from 0.34 for the undoped material to 0.83 for the 40 mol% Sn4+ doped counterpart. The Sn4+ doping led to the change of lattice distortion and crystal growth pattern of NaYF4:Yb3+/Er3+. The mechanism for Sn4+ doping to affect the luminescence properties of the prepared upconversion material was also explored. The changes in luminescence intensity levels and R/G ratios could be attributed to the highly asymmetric distorted lattice and crystal field resulting from Sn4+ doping.

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.

Effects of optically inert ions on up-conversion luminescence and temperature-sensing properties of Y2O2S: Er3+/Yb3+/Tm3+ phosphors

The quenching of luminescence in Er3+/Yb3+ co-doped with Tm3+ presents a dilemma as it substantially diminishes thermometric performance. In this study, Y2O2S: Er3+/Yb3+/Tm3+ phosphors were synthesized using a homogeneous precipitation method combined with a sulfurization process. In addition, three sets of fluorescence intensity ratio (FIR) models were designed, which have self-calibration function. The effects of incorporation of Li+ or Li+/Ba2+ on the up-conversion luminescence (UCL) intensity and thermometric performance of the phosphors were systematically studied. The results show that the introduction of Li+ or Li+/Ba2+ co-doping leads to lattice distortion and the formation of oxygen ion vacancies in the lattice, which further accelerates the energy transfer process and mixes the charge transfer states, and ultimately dramatically improves the UCL and thermometric performance. The introduction of Li+ and Li+/Ba2+ co-doping enhanced the UCL of the materials by about 3.7 times and 5.6 times compared to Y2O2S: Er3+/Yb3+/Tm3+. When based on nonthermally coupled levels (NTCLs), the Sr-max of Li+/Ba2+ co-doped sample is 0.080 K−1 at 573 K, which is 87 % higher than that based on TCLs. These findings not only provide a new avenue for improving the UCL and thermometric performance but also provide an accurate self-calibration FIR model over a wide temperature range.

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

Extremely intense pure green upconversion luminescence in Ho3+/Yb3+ co-doped BiTa7O19 phosphors under 980 nm laser excitation

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.

Equal Rights for Activators – Ytterbium to Terbium Cooperative Sensitization in Molecular Upconversion

AbstractMolecular scaffolds are ideal for investigating upconversion (UC) at the highest spatial resolution and to create precisely controllable luminescent materials. Such control may be the key to overcoming the limitations of brightness and reproducibility found in UC micro‐ and nanoparticles. Cooperative UC can significantly increase luminescence brightness and bulk studies showed that highest efficiencies can be obtained by sensitizer‐to‐activator ion ratios ≥ 2, that is, via high probabilities of sensitizing the emitting lanthanide ion. Using nonanuclear molecular complexes, the authors demonstrate both experimentally and theoretically that interion distances are more relevant and that the highest UC efficiencies are actually attained for sensitizer‐to‐activator ion ratios around 1. By modeling accretive and cooperative sensitization UC, energy migration, and fitting experimental data, it is revealed that cooperative sensitization is predominant for the determination of UC luminescence intensities, whereas energy migration defines UC luminescence kinetics. The implementation of interion distances and different energy transfer mechanisms into advanced modeling of experimental UC data will be paramount for designing brighter and better UC materials.

Novel CeF3:Tm3+, Er3+ nanoparticles: NIR up-down conversion luminescence properties based on energy transfer of Tm3+ and Ce3+

A novel CeF3:Tm3+, Er3+ NIR up-down conversion luminescent nanoparticles with highly efficient visible and near-infrared second window (NIR-II) emission were synthesized by direct precipitation and hydrothermal methods. The two different emission modes of visible-NIR II light of Er3+were realized through the energy transfer of Tm3+ and Ce3+at the excitation wavelength of 808 nm. Which successfully combined the narrow emission peaks of visible light and the deep tissue penetration advantage of NIR-II. First, the effects of preparation conditions on the structure, morphology, stability and luminescence properties of CeF3:Tm3+, Er3+ nanoparticles were analyzed by XRD, SEM, TEM and PL. The results showed that the crystallinity, morphology and luminescence intensity of CeF3:Tm3+,Er3+ nanoparticles produced by hydrothermal method (reaction time of 10 h) were optimal compared with that of direct precipitation method. CeF3: Tm3+,Er3+ nanoparticles has better thermal stability, and fluorescence lifetime of 5D0→7F2 (525 nm), 4I15/2→4I11/2 (1066 nm) and 4I15/2→4I13/2 (1386 nm) for Er3+ are 15.51 ns, 48.78 us and 57.06 us, separately. At the same time, the surface of CeF3:Tm3+, Er3+ nanoparticles was modified by PEG and Lys. And then the effects of the surface modification on the hydration size, zeta potential and up-down conversion luminescent properties (visible and NIR-II light emission) were investigated. The results show that the modification of PEG effectively slows down the agglomeration of CeF3:Tm3+, Er3+ nanoparticles and improves their stability and dispersion under the same conditions. More importantly, the modification of PEG effectively increases the up-conversion luminescence intensity of CeF3:Tm3+, Er3+ nanoparticles under 808 nm excitation. Moreover, the CeF3:Tm3+, Er3+-PEG nanoparticles with 20–40 nm showed stronger NIR up-down conversion emission intensity in aqueous solutions (pH = 5,6,7) and better thermal stability. Furthermore, the CeF3:Tm3+, Er3+-PEG nanoparticles has low cytotoxicity and good biocompatibility. This study provides a theoretical basis for the development of high-performance rare-earth NIR up-down conversion luminescence materials.

Behavior of Microstrain in Nd3+-Sensitized Near-Infrared Upconverting Core-Shell Nanocrystals for Defect-Induced Tailoring of Luminescence Intensity.

In an attempt to optimize the upconversion luminescence (UCL) output of a Nd3+-sensitized near-infrared (808 nm) upconverting core-shell (CS) nanocrystal through deliberate incorporation of lattice defects, a comprehensive analysis of microstrain both at the CS interface and within the core layer was performed using integral breadth calculation of high-energy synchrotron X-ray (λ = 0.568551 Å) diffraction. An atomic level interpretation of such microstrain was performed using pair distribution function analysis of the high-energy total scattering. The core NC developed compressive microstrain, which gradually transformed into tensile microstrain with the growth of the epitaxial shell. Such a reversal was rationalized in terms of a consistent negative lattice mismatch. Upon introduction of lattice defects into the CS systems upon incorporation of Li+, the corresponding UCL intensity was maximized at some specific Li+ incorporation, where the tensile microstrain of CS, compressive microstrain of the core, and atomic level disorders exhibited their respective extreme values irrespective of the activator ions.