Upconversion Emission Intensity Research Articles

Upconversion Luminescence with Bis-pyclen Yb(III) Chelates: Crown vs. Linear Polyether Linkers in Discrete Heteropolynuclear Architectures.

Ligands combining two lateral bis-pyridyl-phosphonated-pyclens were synthesized, using a flexible linear pegylated linker (L2) or a bulkier K22 crown-ether (L3). A functionalized pyridyl-phosphonated-pyclen (L1) was also prepared as a mononuclear analogue. Coordination behavior of lanthanide cations was studied via NMR titration with Lu for L1, and UV/Vis and luminescence spectroscopy with Yb for L2/L3. Strong coordination of two Yb atoms enabled isolation and spectroscopic characterization of dinuclear complexes in H2O and D2O. Excited state lifetime analysis at 980 nm revealed strong protection of Yb cations, with no coordinated water molecule. Upon titration of the isolated dinuclear Yb complexes with Tb cations, cooperative upconversion (UC) sensitization of Tb in the visible was observed upon excitation of Yb at 980 nm in D2O. In the absence of Tb, the Yb complexes also exhibited cooperative luminescence with a weak emission band around 500 nm upon NIR Yb excitation. Efficient UC with Tb was only observed after thermal treatment, suggesting a slow kinetic of formation of the UC species. [Yb2TbL3] showed weak Tb centered UC emission, while the dinuclear complex of L2 displayed more intense UC emission up to two equivalents of Tb, forming [(Yb2L2)Tbx] (x=1-2), with the tetranuclear heterometallic complex being the most intense emitter. Log-Log plot analysis confirmed the two-photon nature of the UC process.

Upconversion Luminescence with Bis‐pyclen Yb(III) Chelates: Crown vs. Linear Polyether Linkers in Discrete Heteropolynuclear Architectures

Ligands combining 2 lateral bis‐pyridyl‐phosphonated‐pyclens were synthesized, using a linear pegylated linker L2 or a K22 crown‐ether L3. A functionalized pyridyl‐phosphonated‐pyclen L1 was also prepared as a mononuclear analogue. Coordination behavior of lanthanide cations was studied via NMR titration with Lu for L1, UV‐Vis and luminescence spectroscopy with Yb for L2/L3. Strong coordination of two Yb atoms enabled isolation and spectroscopic characterization of dinuclear complexes in H2O and D2O. Excited state lifetime at 980nm revealed strong protection of Yb cations, with no coordinated water. Upon titration of the isolated dinuclear Yb complexes with Tb cations cooperative upconversion (UC) sensitization of Tb in the visible was observed (excitation of Yb, 980nm, D2O). In absence of Tb, the Yb complexes also exhibited cooperative luminescence with a weak emission band around 500nm upon NIR Yb excitation. UC with Tb was only observed after thermal treatment, suggesting a slow kinetic of formation of the UC species. [Yb2TbL3] showed weak Tb centered UC emission, while the dinuclear complex of L2 displayed more intense UC emission up to two equivalents of Tb, forming [(Yb2L2)Tbx] (x=1‐2), with the tetranuclear heterometallic complex being the most intense emitter. Log‐Log plot analysis confirmed the 2‐photon nature of the UC process.

Pressure-assisted sintering approaches for up-converting LiYF4:Er/Yb transparent oxyfluoride glass-ceramics

Glasses of compositions 40SiO2-25Al2O3-18Li2O-7LiF-(10-x-y)YF3-xErF3-yYbF3 (mol.%, x = 0.1, 0.5; y = 0, 0.4, 2, 4) were prepared by melt-quenching technique and milled into powders. Glass powder pellets were treated by hot pressing at defined temperatures to obtain the corresponding glass-ceramics (GCs). High-resolution TEM and XRD analysis revealed the crystallization of LiYF4 and LiAlSiO4 phases with nano-crystal size below 50 nm, resulting in translucent GCs. The density of GCs was 98–99.5 % compared to parent glasses. GCs exhibited intense up-conversion emission when excited by near-infrared light at 980 nm. As Er3+ concentration increased from 0.1 to 0.5 mol.% in the samples, notable enhancement in green and red emission intensities was indicated. Yb3+ ions significantly facilitated up-conversion emission through energy transfer to Er3+ ions, resulting in a higher luminescence yield compared to Er3+ single-doped GCs. The tuning of the red to green emission intensity ratio can be achieved by varying Er3+ and Yb3+ concentrations and Er3+/Yb3+ ratio.

Effects of alkali ions on the optical properties, bandwidth flatness, and gain coefficient of near-infrared emission spectra of Er3+-doped zinc silicate glass

In this paper, we investigate and report the effects of alkali ions A+ (A+ = Li+, Na+, K+) on the optical properties, bandwidth flatness (BFN), gain coefficient (G(λ)) for the near-infrared (NIR) emission spectra of Er3+-doped SiO2–ZnO–La2O3 (SZL) zinc silicate glass. With the change in the composition of A+ ions in the order from not containing any A+ ions → Li+ → Na+ → K+ → containing all three A+ ions including Li+, Na+, and K+, the direct and indirect bandgap (DBG and IBG), the absorption cross-section (σabs(λ)), the emission cross-section (σems(λ)), and the G(λ) parameters of Er3+-doped SZL glasses were determined to increase gradually. NIR emission intensities of Er3+-doped at 4I13/2 → 4I15/2 transition under excitations of both 808 and 980 nm LD all were significantly increased with the composition of A+ ions varies in order from not containing A+ ions → Li+ → Na+ → K+ → containing all three A+ ions. The reasons for the influence of A+ ions on the UC and NIR emission intensities of Er3+-doped in SZL glass are investigated and discussed. In addition, upconversion (UC) emission spectra of Er3+-doped, CIE 1931(x; y) coordinates and color region for UC emission spectra of Er3+-doped SZL glasses with different compositions of A+ ions under excitation of 980 nm laser diode (LD) are also determined.

New Horizons for Temperature Sensing and Bioimaging Using Er3+‐Doped Core@Shell Nanoparticles and Effects of H2O and D2O Solvents on Their Spectroscopic Properties

AbstractLanthanide‐doped nanoparticles (NPs) exhibit temperature‐dependent luminescence, enabling the design of luminescent nanothermometers for industrial and medical applications. This research demonstrates the temperature‐sensing properties of NaYF4:7.5%Er3+@NaYF4 and NaErF4@NaYF4 NPs, which have a hexagonal shape and average size of 17 nm. Their core@shell structure is confirmed using high‐resolution transmission electron microscopy, and they exhibit intense upconversion (UC) emission under 1532 nm excitation in H2O and D2O colloids. The recorded spectra show Er3+ emission bands with varying intensity ratios depending on the Er3+ concentration, chosen solvent, and temperature. The spectroscopic properties of the studied NPs allow for their excitation and observation of emission within biological windows, which makes them useful for bio‐related applications. The emission of prepared NPs is analyzed as a function of temperature from 298 up to 358/363 K in H2O and D2O. The ratios for thermally‐coupled levels and non‐TCLs and their relative sensitivities are studied. For the high dopant concentration sample in water, the O─H vibrations and blue shift in the absorption spectrum lead to a record relative sensitivity of 2.50% K−1 (at 363 K) for the 2H11/2/4I11/2 ratio. The use of synthesized NPs for bioimaging under 1550 nm excitation is also demonstrated to observe their accumulation in the guts of Daphnia magna.

Ultrasensitive and Adjustable Nanothermometers Based on Er3+-Sensitized Core@Shell Nanoparticles for Use in the First Biological Window.

In recent years, intensive research has focused on lanthanide-doped nanoparticles (NPs) used as noncontact temperature sensors, particularly in nanomedicine. These NPs must be capable of excitation and emission within biological windows, where biological materials usually show better transparency for radiation. In this article, we propose that NPs sensitized with Er3+ ions can be applied as temperature sensors in biological materials. We synthesized the NPs through a reaction in high-boiling solvents and confirmed their crystal structure and the formation of core@shell NPs by using X-ray diffraction, high-resolution transmission electron microscopy, and element distribution mapping within the NPs. NaErF4@NaYF4, NaYF4:12.5% Er3+, 2.5% Tm3+@NaYF4, NaYF4:7.5% Er3+@NaYF4, and NaYF4:12.5% Er3+, 2.5% Ho3+@NaYF4 exhibited intense upconversion (UC) emission under 1532 nm laser excitation detectable also in the whole human blood. We propose that this UC results from energy transfer between Er3+ ions and from Er3+ to Tm3+ or Ho3+ codopants. To determine the mechanism of UC, we measured the dependence of the emission band intensities on the laser power densities. Importantly, we also analyzed the temperature-dependent emission of the NPs within the 295-360 K range. Based on the collected emission spectra, we calculated the luminescence intensity ratios (LIRs) of the emission bands to assess their potential for optical temperature sensing. The temperature-sensing properties varied with the concentration of Er3+ ions and the presence of additional Tm3+ or Ho3+ codopants. Depending on the NP composition and the emission bands used for luminescence ratio calculations, the maximum relative temperature sensitivity ranged from 4.55%·K-1 to 1.12%·K-1, with temperature resolution between 0.05 and 2.53 K at room temperature. Finally, as proof of using NPs as temperature sensors in biomedicine, we successfully measured the temperature-dependent emission of NaYF4:7.5% Er3+@NaYF4 NPs dispersed in whole blood under 1532 nm excitation. We demonstrated that the ratio of Er3+ ion emission bands changes with temperature, indicating that these NPs have potential applications in temperature sensing within biological environments. We also confirmed the properties of NPs as temperature sensors by measuring the temperature reading uncertainty and the repeatability of the LIR readings during heating-cooling cycles, thereby confirming the excellent properties of the studied systems as temperature sensors.

Up-Conversion Emissions from HfO2: Er3+, Yb3+ Nanoparticles Synthesized by the Hydrothermal Method.

Up-conversion emission from HfO2 nanoparticles, as a host lattice, doped with Er3+ and Yb3+ ions and codoped with alkaline cations Li+ and Na+ obtained. The HfO2 nanoparticles, about 80 nm in diameter, were synthesized by the hydrothermal method at 200 °C for 1.3 h, and an additional heat treatment at 1000 °C was necessary to ensure the dopants incorporation into the host lattice. These nanoparticles were studied by means of XRD, Raman Spectroscopy, SEM, EDS, PL, CL, and up-conversion luminescence. First, the doping was performed with Er3+ ions in different percentages. The photoluminescence and cathodoluminescence studies showed an inefficient emission, and only at 7 at % Er3+ ions, the sample presented emissions at 522, 545, and 656 nm corresponding to the transitions of the Er3+ ions. So, codoping was carried out, and HfO2: Er3+/Yb3+ generated an efficient conversion process. The atom percentage of Yb3+ ions was fixed (7 at % Yb3+), and the Er3+ content was varied, showing the highest emission intensity at 3 at % Er3+ ions. Subsequently, the up-conversion emission intensity was optimized by varying the percentage of Yb3+ ions and keeping the Er3+ ion content fixed (3 at %). Adding cations such as Na+ and Li+ in different percentages, a notable improvement of the up-conversion emission intensities in the HfO2: Er3+/Yb3+ nanoparticles was obtained. The up-conversion emission bands observed were located at ∼523 and 544 nm, corresponding to the electronic transitions 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively. While the bands at ∼652 and 673 nm correspond to the transition 4F9/2 → 4I15/2, respectively. The excitation of these materials with infrared radiation (980 nm) produced noticeable emission bands in the red spectral range, whereas excitation with accelerated electrons (CL) generated prominent bands in the green region.

An Integrated Nanoplatform via Dual Channel Excitation for Both Precise Fluorescence Imaging and Photodynamic Therapy of Orthotopic Breast Tumor in NIR-II Region.

Although research on photodynamic therapy (PDT) of malignant tumor has made considerable progress in recent years, it is a remaining challenge to extend PDT to the second near-infrared window (NIR-II) along with real-time and accurate NIR-II fluorescence imaging to determine drug enrichment status and achieve high treatment efficacy. In this work, lanthanide nanoparticles (Ln NPs)-based nanoplatform (LCR) equipped with photosensitizerChlorin e6 (Ce6) and targeting molecular NH2-PEG1000-cRGDfK aredeveloped, which can achieve NIR-II photodynamic therapy (PDT) and NIR-II fluorescence imaging by dual channel excitation. Under 808nm excitation, Nd3+ in the outer layer can absorb the energy and transfer inward to emit strong NIR-II emissions (1064 and 1525nm). Due to the low background noise of NIR-II light and the targeting effect of NH2-PEG1000-cRGDfK, LCR can recognize tiny tumor tissue (≈3mm) and monitor drug distribution in vivo. Under 1530nm excitation, internal Er3+ can be self-sensitized, generating intense upconversion emission (662nm) that can effectively activate Ce6 for in vivo PDT due to the deep tissue penetration of NIR-II light. This study provides a paradigm of theranostic nanoplatform for both real-time fluorescence imaging and PDT of orthotopic breast tumor in NIR-II window.

Tuning the 5d State of Pr3+ in Oxyhalides for Efficient Deep Ultraviolet Upconversion

AbstractVisible‐to‐ultraviolet (UV) upconversion provides a fascinating strategy to achieve deep UV emission through readily accessible visible light. However, the intensity of deep UV emission obtained through visible‐to‐UV upconversion progress is still far from satisfactory, severely constraining its practical applications. Herein, a novel class of praseodymium ion (Pr3+)‐doped rare‐earth oxyhalides (YOCl, YOBr, and LuOBr) to achieve efficient upconverted deep UV emission in the spectral range of 250–350 nm is developed. The upconverted UV emission intensity of LuOBr:Pr3+ is determined to be 56.7 times stronger than that of the well‐established Lu7O6F9:Pr3+. When employed as a photon‐converter to activate photocatalytic water splitting reactions, upconverted deep UV emission enables H2 generation under visible light (λ > 420 nm) excitation from a xenon lamp. The efficient deep UV upconversion stems from tuning 4f15d1 state of Pr3+ by oxyhalide constituent which both facilitates the absorption of excitation photons in long‐lived intermediate 4f2 states and suppress the probability of nonradiative relaxation from 4f15d1 state. These findings not only provide new insights into a mechanistic understanding of the host effect on upconversion process but also make a breakthrough in developing efficient deep upconversion materials that will expand their further applications.

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.

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.

Upconversion multicolor tuning in Er3+ and Yb3+ doped yttrium oxide prepared by precursor technique

The (Y0.9Er0.1-xYbx)2O3 (x = 0, 0.02, 0.05, 0.07, 0.08, 0.09) and Y1-(0.02+y)Er0.02YbyO3 (y = 0.05, 0.07, 0.09, 0.11) solid solutions have been synthesized by the precursor technique using mixed anhydrous formates. The crystal structure of ytterbium formate, Yb(HCOO)3, was established for the first time. The structural parameters and phase purity of the synthesized precursors and oxides were determined by X-ray phase analysis. The average sizes of crystallites are in the 60–80 nm range. The upconversion spectra of solid solutions exhibit a weak green and an intense red line attributed to 2H11/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions. The green and red emissions of (Y0.9Er0.1-xYbx)2O3 and Y1-(0.02+y)Er0.02YbyO3 oxides are caused by two-photon conversion processes. The effect of dopant (erbium and ytterbium) concentration and Er3+/Yb3+ ratio on the intensity of upconversion emission were established, the contribution of upconversion green luminescence decreases with increasing the ytterbium concentration.

Upconversion Emission and Dual-Mode Sensing Characteristics of NaYF4:Yb3+/Er3+ Microcrystals at High and Ultralow Temperatures.

In this study, we investigate micrometer-sized NaYF4 crystals double-doped with Yb3+/Er3+ lanthanide ions, designed for temperature-sensing applications. In contrast to previous studies, which focused predominantly on the high-temperature regime, our investigation spans a comprehensive range of both high and ultralow temperatures. We explore the relationship between temperature and the upconversion luminescence (UCL) spectra in both frequency and time domains. Our findings highlight the strong dependence of these spectral characteristics of lanthanide-doped NaYF4 crystals on temperature. Furthermore, we introduce a dual-mode luminescence temperature measurement technique, leveraging the upconversion emission intensity ratio for both green and red emissions. This study also examines the correlation between temperature sensing, energy level disparities, and thermal coupling in Er3+ ions across various temperature scales. Our research contributes to advancing the understanding and application of lanthanide-doped materials, setting a foundation for future innovations in temperature sensing across diverse fields.

Efficient green upconversion emission in transparent Teo2-Geo2 glass-ceramic obtained by billet extrusion

Transparent Yb3+/Er3+glass-ceramic was successfully obtained by the extrusion method. The extrusion of oxyfluoride tellurite-germanate glass co-doped with Yb3+and Er3+ions at 520°C resulted in the formation of Ba0:75Er0:25F2:25 nanocrystals, leading to an increase in the upconversion (UC) emission intensity of 35 times in glass-ceramic with respect to the glass. The glass to glass-ceramic transition was confirmed by X-ray diffraction (XRD) and Transmission electron microscope (TEM). Also, the structural changes that occurred during crystallization were assessed using Fourier-transform infrared (FTIR) spectroscopy. Furthermore, the pump power and temperature UC emission dependence of glass and glass-ceramic under 976 nm laser excitation were investigated in detail. The assessments showed that i) two-phonons are involved in the UC process and ii) the temperature has a significant influence over it. The Yb3+/Er3+ codoped glass-ceramic shows relatively high Sa and Sr values in a wide temperature range from 300 to 573 K, presenting the maximal Sa value of 3:50 x 10–3 at 573 K and the maximal Sr value of 6:30 x 10–3at 364 K. These results suggest that the glass-ceramic is a good candidate for optical applications such as luminescent thermometry.

Preparation and optical properties of rare earth fluoride and its related composite materials

Rare earth fluoride and its composite materials have shown broad application prospects in fields such as optoelectronics and photocatalysis. In this study, we prepared rare earth fluoride (β-NaYF4 nanocrystals) and its related composite materials (β-NaYF4/ZnO composite and GQDs@NaYF4 nanomaterials) using a solvothermal method and investigated their optical performance. The characterization and performance of the prepared materials were analyzed using a transmission electron microscope, X-ray diffraction, upconversion emission spectra, and fluorescence lifetime imaging microscopy. The results show that the crystal thickness of β-NaYF4 nanocrystals is approximately 45.0 nm when the F−: Ln3+ value is 6. Furthermore, X-ray diffraction analysis reveals that diffraction peak positions in β-NaYF4 nanocrystals correspond to the peak positions of standard card at different doping concentrations of Zn2+ Moreover, it was observed that the highest fluorescence lifetime of Tm3+ ion in 1G4 is 778 μs when the doping concentration of Zn2+ is 1 mol%. When the concentration of exonuclease III increases to 22.5U, the upconversion fluorescence emission intensity of GQDs@NaYF4 nanomaterial is about 34 ∗ 106 a.u. When the activation reaction time is 90 minutes, the upconversion emission intensity of GQDs@NaYF4 nanomaterial is about 37 ∗ 106 a.u. In conclusion, we successfully prepared rare earth fluoride and its composite materials with excellent optical properties through the solvothermal method.

Multi-mode excited upconversion and downshifting of Ho3+/Yb3+ doped lead-free double perovskite Cs2NaBiCl6 for anti-counterfeiting and thermometry

Rear earth(RE)-doped halide perovskite has generated as an amazing optical material for multicolor luminescence. Free-lead halide double perovskites have attracted interesting because of their non-toxicity and higher instability. Here, RE3+ doped chloride-based double perovskite phosphors are reported. A series of heavy concentration Ho3+/Yb3+ doped Cs2NaBiCl6(CNBC) phosphors are prepared with a solvothermal route. The band structure of CNBC is calculated through density functional theory (DFT). The luminescence properties of CNBC:Ho3+ and CNBC:Ho3+/Yb3+ are investigated through upconversion(UC) and downshifting(DS) processes. From CNBC:Ho3+, the brightness orange, deep red and pale green lights are achieved under excitation at 365, 452 and 980 nm. The multicolor emissions of CNBC:Ho3+ are used to multimode fluorescent anti-counterfeiting. Comparing with CNBC:Ho3+ samples, the UC emission intensity of CNBC:Ho3+/Yb3+ are dramatically enhanced. The brightness green light can be seen by naked eyes under super lower power pumping(∼10 mW). The temperature sensing properties of CNBC:Ho3+/Yb3+ phosphor are investigated systematically based on the luminescence intensity ratio(LIR) of thermally coupled levels(TCLs)(5F1/5G6,5F2,3/3K8) and non-TCLs(5F4/5S2,5F5). The maximum relative sensitivity(SR) reaches 5.089% K−1 at 293 K according to the LIR of non-TCLs. The work will broaden the application field of RE3+-doped free-lead perovskite such as anti-counterfeiting and thermometry.

Nanocrystals Incorporated with Mordenite Zeolite Composites with Enhanced Upconversion Emission for Cu2+ Detection.

In this research, upconversion nanocrystals incorporated with MOR zeolite composites were synthesized using the desilicated MOR zeolite as a host for the in situ growth of NaREF4 (RE = Y, Gd) Yb/Er nanocrystals. The structure and morphology of the composites were studied with XRD, XPS, and TEM measurements, and the spectral studies indicated that the subsequent thermal treatment can effectively improve the upconversion emission intensity of Er3+. By using the NaYF4:Yb/Er@DSi1.0MOR-HT composite that holds the strongest upconversion emission, a probe of UCNC@DSiMOR/BPEI was constructed with the modification of branched poly ethylenimine for the detection of Cu2+. It was indicated that the integrated emission intensity of Er3+ shows a linear dependence with the logarithm value of the Cu2+ concentration ranging from 0.1 to 10 μM. This study offered a feasible method for the construction of UCNC@zeolite composites with enhanced upconversion emission, which may have a potential application as fluorescent probes for the detection of various metal ions by adjusting the doping luminescent center.

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.

Blue and green upconverted emission in fluoroindate glasses under 808 nm excitation

In this study, the upconversion (UC) luminescence of fluoroindate glasses (InF3G) co-doped with Yb-Nd-Er (Tm) ions excited in the NIR-I biological window was analyzed. In the first system, UC emission of singly Er3+ doped InF3G under 808 nm excitation occurred to be more efficient than those observed in InF3G co-doped with Yb–Er and Yb-Nd-Er. The intensity of UC emission (InF3G-Er) was 22 % higher than InF3G-Yb-Er, and even more than two times higher than in the InF3G-Yb-Nd-Er sample. The effective energy transfer (η) between Nd3+- Yb3+ (η = 45 %) and Yb3+-Er3+ (η = 68 %), was reflected in the emission observed in the NIR region mainly, ascribed to Yb3+:2F5/2 → 2F7/2 (978 and 999 nm) and Nd3+:4F3/2 → 4I9/2 (1053 nm) transitions. Meanwhile, the samples co-doped with Tm3+ exhibited a strong dependence on Yb-Nd-Tm co-doping. Samples without Yb and Nd did not exhibit any UC emission due to the absence of pumping channel. This contrasts with the downshifting NIR emission, which was at least two times higher than those exhibited in samples co-doped Yb-Nd-Er. These results suggest that Tm3+ plays a crucial role in populating the lower-lying exited levels of Yb and Nd, influencing the overall emission behavior.

Optimizing the composition of LaF3:Yb,Tm upconverting nanoparticles synthesised by the co-precipitation method to improve the emission intensity.

LaF3:1-6 mol%Yb3+,0.1 mol%Tm3+ nanoparticles with upconversion properties were synthesised by the co-precipitation method. Particles were characterized by transmission electron microscopy coupled with energy-dispersive spectrometry, inductively coupled plasma optical emission spectrometry, X-ray diffraction, and simultaneous thermogravimetry and differential thermal analysis. Upconversion properties were investigated by fluorescence spectroscopy, using 980 nm laser light excitation. The results show that the particles had a hexagonal LaF3 crystal structure. Crystallite and particle sizes decreased with increasing Yb3+ content and the average crystallite size changed between 18 and 36 nm, while the average particle diameter was 25-52 nm. The highest upconversion emission intensity at the 480 nm emission peak could be reached with an optimal Yb3+ content of 3 mol% and an Yb/Tm ratio of ∼75. These upconverting nanoparticles, prepared using a cheap and environmentally friendly co-precipitation method and containing relatively low dopant ion concentrations, will be helpful in a variety of promising fields, such as sensing, solar cells and security applications.