Enhanced Upconversion Luminescence Research Articles

Enhancement of Upconversion Luminescence through Three-Dimensional Design of Plasma Ti3O5-Coupled Structural Domain-Limiting Effects.

Upconversion luminescence plays a crucial role in various technological applications, and among the various valence states of lanthanide elements, Ln3+ has the highest stability. The 4f orbitals of these elements are in a fully empty, semifull, or full state. This special 4f electron configuration allows them to exhibit rich discrete energy levels. However, the 4f-4f transition of Ln3+ rare earth ions itself is prohibited, resulting in a lower luminescence efficiency. This limitation greatly hinders the practical application of upconversion luminescence. In this study, we report nanostructured luminescence-enhanced substrate platforms with both semiconductive local surface plasmons and spatially confined domain effects on a single defect semiconductor substrate. By coupling NaYF4:Yb-Er nanoparticle emitters to the surface of Ti3O5 NC-arrays plasmonic nanostructures, an ultrabright luminescence with a 32-fold increase in green emission and a 40-fold increase in red emission was achieved. Furthermore, the fluorescence resonance energy transfer characteristics observed in the R6G/NaYF4/Ti3O5 NC-array composite film enable accurate detection of fluorescent molecules. The results provide an innovative and intelligent approach to enhance the upconversion luminescence intensity of rare-doped nanoparticles and develop highly sensitive molecular detection systems based on the above luminescence enhancement.

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.

Enhanced upconversion luminescence of NaYF4:Er nanocrystals based on the synergy between whispering gallery mode excitation and förster resonant energy transfer

The upconversion luminescence at the visible band was excited by the high power density whispering gallery mode (WGM) on the surface of the microsphere. Under the WGM excitation, Er3+ of NaYF4:Er3+ directly absorbed three photons at 1525 nm, followed by the generation of upconversion luminescence. We used WS2 quantum dots (QDs) as donors and NaYF4:Er3+ upconversion nanoparticles (UCNPs) as acceptors to enhance upconversion luminescence by Förster resonant energy transfer (FRET). The physical mixture composed of monolayer WS2 and NaYF4:Er3+ nanoparticles was coated on SiO2 microsphere by immersion method. Excited by high power density WGM, three photons were absorbed by WS2-QDs based on the quantum size effect to generate excited electrons as donors and UCNPs as acceptors based on FRET, subsequently, the energy of the electrons were transferred to the luminescence center Er3+ to improve the upconversion luminescence efficiency. The mechanism model of upconversion luminescence enhancement based on FRET of WS2–NaYF4:Er3+ was proposed, and the enhancement effect was experimentally studied and demonstrated. To study the distance dependence of energy transfer between QD and UCNP pairs, we covered the surface of the silica microsphere with a controlled concentration of WS2 mixed with NaYF4:Er3+ nano-particles. When the mixed concentration of WS2-QDs was 0.15%, the upconversion luminescence reached the highest efficiency. The results showed that a twofold upconversion luminescence enhancement can be experimentally achieved. The proposed approach for enhancing the upconversion luminescence could benefit the improvement of imaging signal-to-noise ratio (SNR) using UCNPs for fluorescent labels in life sciences.

Brownian Motion Governs the Plasmonic Enhancement of Colloidal Upconverting Nanoparticles.

Upconverting nanoparticles are essential in modern photonics due to their ability to convert infrared light to visible light. Despite their significance, they exhibit limited brightness, a key drawback that can be addressed by combining them with plasmonic nanoparticles. Plasmon-enhanced upconversion has been widely demonstrated in dry environments, where upconverting nanoparticles are immobilized, but constitutes a challenge in liquid media where Brownian motion competes against immobilization. This study employs optical tweezers for the three-dimensional manipulation of an individual upconverting nanoparticle, enabling the exploration of plasmon-enhanced upconversion luminescence in water. Contrary to expectation, experiments reveal a long-range (micrometer scale) and moderate (20%) enhancement in upconversion luminescence due to the plasmonic resonances of gold nanostructures. Comparison between experiments and numerical simulations evidences the key role of Brownian motion. It is demonstrated how the three-dimensional Brownian fluctuations of the upconverting nanoparticle lead to an "average effect" that explains the magnitude and spatial extension of luminescence enhancement.

Thermal Enhancement of Upconversion in Sub‐10 nm Yb3+/Er3+/Na+ Tridoped Cs2ZrF6 Nanocrystals for Ratiometric Temperature Sensing

AbstractAlkaline zirconium fluorides (AxZryFx+y, A = Li, Na, and K), featuring unique crystallographic structures, have recently emerged as a class of attractive hosts for fabricating lanthanide (Ln3+)‐doped upconversion nanocrystals (UCNCs) that exhibited distinct morphology, upconversion luminescence (UCL) performance, and physicochemical property. In this paper, for the first time the controlled preparation of Yb3+/Er3+‐doped UCNCs is reported based on the trigonal Cs2ZrF6 host, leading to tunable morphology and size of the resulting UCNCs by varying the reaction temperature and time. By further incorporating Na+ ions into the Cs2ZrF6 crystal lattice, sub‐10 nm Yb3+/Er3+/Na+ tridoped UCNCs with highly improved crystallinity and thus greatly enhanced UCL intensity are obtained. Moreover, these resulting UCNCs display abnormal thermal enhancement of UCL over a temperature range from 333 to 493 K, enabling the fabrication of supersensitive luminescent nanothermometers for temperature sensing. Based on the luminescence intensity ratio of two nonthermally coupled levels (i.e., 4F9/2 and 2H11/2) of Er3+, the as‐prepared Cs2ZrF6:Yb/Er/Na UCNCs exhibit an extremely large absolute sensitivity of 177.3% K−1 and a considerably high relative sensitivity of 1.52% K−1 at 333 K. These results unambiguously demonstrate that Cs2ZrF6 is a suitable host material for preparing small‐sized Ln3+‐doped UCNCs as nanothermometer for high‐performance ratiometric temperature sensing.

Enhanced up-conversion luminescence and temperature sensing performance of NaBiF4: Er3+, Yb3+, Al3+

Rare earth doped fluoride-based up-conversion luminescent materials have been widely studied in non-contact temperature sensing technology. However, the luminous intensity of the fluoride at high temperature still needs to be improved. Here, enhanced up-conversion luminescence and temperature sensing performance of NaBiF4: Er3+, Yb3+ is realized by Al3+ substitution. The samples exhibit the characteristic green (521 nm and 540 nm) and red (654 nm) emissions of Er3+ ion under 980 nm excitation. When the concentration of Al3+ is 5%, the green emission is enhanced by about 10 times, and the red light is enhanced by about 7 times. Obvious lattice shrinkage caused by the introduction of Al3+ is responsible for the enhancement. In addition, the optimal sample is highly thermally stable from 303 K to 443 K. The maximum relative sensitivity at 303 K increases from 0.791% K−1 to 1.106% K−1. The results indicate that NaBiF4: Er3+, Yb3+, Al3+ be a potential thermosensitive material.

Phase-separation enhanced upconversion luminescence with regulated pure-red emission in manganese fluorosilicate glass

In this work, rare earth ions (REs) including Yb3+/Er3+, Yb3+/Ho3+ and Yb3+/Tm3+ co-doped manganese oxyfluoride glasses were fabricated using melt quenching method. By fully utilizing the upconversion luminescence (UCL) of REs and regulating energy transfer between the different energy levels of RE ions and the 4T1 level of Mn2+, the output of UCL was regulated and even pure-red light can be achieved. Moreover, owing to the selective partitioning caused by phase-separation network structure in the oxyfluoride glass, the UCL intensity of glasses annealed for 72 h is significantly enhanced 58 times compared to the rapidly quenched samples.

Systematic study on the intensified upconversion performance of LaVO4:Yb3+/Er3+ nanocrystals through Ti4+ ions doping by combining experiments and DFT calculations

The inherent low-efficiency for upconversion fluorescence materials constricts their further applications in many research domains. Over the last decades, considerable efforts have been paid to the fluorides, less works concering LaVO4 are reported. Based on series of impurity content-dependent experiments, Ti4+ ions doped LaVO4:Yb3+/Er3+ crystals are hydrothermally fabricated. The products are characterized by XRD, ICP, TEM and luminescence spectroscopy. Through modulating the Ti4+ ions doping concentration, the UCL intensity of 533 nm and 664 nm emissions are greatly intensified. The reasons are analyzed on the basis of three major factors. Meanwhile, extra DFT calculations are performed to support the experimental result. This report paves a new way for enhancing upconversion luminescence intensity of LaVO4 nanocrystals based on impurity doping.

Li+-induced triple optimization strategy for enhancing upconversion luminescence, anti-thermal quenching and optical thermometry performance in Yb2W3O12: Er3+ phosphors

Lanthanide (Ln3+)-doped A2M3O12-type negative thermal expansion (NTE) materials have received increasing attention as luminescent materials with thermal enhancement effects. However, it is highly desirable to develop effective methods to further improve their properties. Herein, the effects of Li+ co-doping on the structure, morphology, hygroscopicity, thermal expansion behavior, upconversion luminescence (UCL) property and optical thermometric performance of Yb2W3O12: Er3+ NTE materials are investigated in detail. X-ray diffraction (XRD) analysis reveals that the preferential occupancy of Li + ions in the void spaces of the Yb2W3O12 structure results in an expansion of host lattice and a slight change of the NTE behavior. Thermal analysis indicates that the presence of Li + ions reduces the intrinsic hygroscopicity of Yb2W3O12. Upon 980 nm excitation, enhancements in both the emission intensity and anti-thermal quenching capacity of Er3+ ions are achieved through the incorporation of 3 mol%Li+, which is mainly attributed to the improved structural rigidity and weakened cross-relaxation processes between Er3+ ions. When the temperature sensing is based on the intensity ratio of 2H11/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions (I527/I659), the absolute sensing sensitivity (Sa-max = 503 × 10−4 K−1) and relative sensitivity (Sr-max = 1.4 %K−1) of Yb2W3O12: 5 %Er3+, 3 %Li+ are higher than those of the sample without Li+ co-doping (Sa-max = 308 × 10−4 K−1, Sr-max = 1 %K−1). The present findings may shed light on optimizing the application performance of Ln3+ ions doped A2M3O12 phosphors.

0D/2D Bi2WO6:Yb3+,Tm3+/Bi12O17Cl2 S-scheme heterojunction photocatalyst with enhanced full spectrum light activity by upconversion luminescence

To effectively utilize near-infrared light in the solar spectrum, expanding the spectral response range of photocatalysts is one of the main issues at present. Herein, a novel 0D/2D Bi2WO6:Yb3+, Tm3+/Bi12O17Cl2 S-scheme heterostructure with full spectral response is successfully synthesized through a hydrothermal method. The optimized Bi2WO6:Yb3+,Tm3+/Bi12O17Cl2 (1:1) photocatalyst degraded 68.2% and 59.1% of methylene blue (MB) and Rhodamine B (RhB) at 980 nm NIR light irradiation for 240 min, and the degradation of MB and RhB was 96.1% and 92.3% under visible light irradiation for 40 min, respectively. The enhanced photocatalytic activity could be attributed to these synergistic effects including the unique 0D/2D contact interface, the expanded photoresponse range, enhanced upconversion luminescence, as well as efficient energy transfer process between Yb3+/Tm3+ and Bi2WO6. Based on characterization and photocatalytic experiments, the introduction of Bi2WO6:Yb3+, Tm3+ can construct S-scheme heterojunctions with Bi12O17Cl2 and produce a full-spectrum response to sunlight. The result, the Bi2WO6:Yb3+, Tm3+/Bi12O17Cl2 photocatalysts possessed effective charge distribution and migration and maintained the excellent redox capacity of semiconductor materials. The hydroxyl radicals (·OH), superoxide radicals (·O2), and holes (h+) as active species played crucial roles in the degradation process. This work describes a potential method to construct S-scheme photocatalyst with great upconversion activity that possesses full spectral response for water pollution control.

Vacuum-assisted colossal enhancement of up-conversion luminescence of lanthanide-doped nanoparticles upon NIR laser irradiation – a new strategy for phosphor development

Permanent enhancement (by 2 orders of magnitude) of up-conversion luminescence via localized crystal growth, induced by NIR laser irradiation under vacuum conditions. This effect is caused by vacuum-enhanced light-to-heat conversion efficiency.

Giant enhancement of anti-quenching upconversion luminescence in Sc2W3O12:Er3+/Yb3+ phosphors for temperature sensing

Although negative thermal expansion (NTE) materials provide a new strategy to overcome the thermal-quenching phenomenon in rare earth doped luminescent materials, the overall weak upconversion luminescence still restrict their application...

Ag-cap-enhanced upconversion luminescence of micropillars with unidirectional radiation

Exploration of plasmonic structures to enhance upconversion luminescence (UCL) attracts attention because faint UCL from a material is a bottleneck for its applications. We designed and prepared three easily realized structures to improve the UCL of β-NaYF4:Yb3, Er3+ micropillar (MP), and compared them to a reference structure on glass on single particles. We achieved a 43-fold UCL enhancement with the MPs with an Ag cap.The experimental results and simulations indicated that the improvements in excitation field and radiation direction collectively enhanced the MP UCL. We validated the captured radiation patterns generated from various structures by excitation simulations and provide a rational criterion for cavity design.

Realizing Superior Luminescence in Oxyfluoride Glass‐Ceramics by Enhancing Nano‐Micro Phase Separation

AbstractIn this work, a novel series of oxyfluoride glasses‐ceramics (GCs) is developed by enhancing the phase separation through the substitution of LaF3 for La2O3. The thus‐derived GCs exhibit a remarkable 2700‐fold increase in up‐conversion (UC) luminescence of Er3+ ions compared to the precursor glass. From the 19F Nuclear Magnetic Resonance analysis, this enhancement is attributed to the structural disorder‐to‐order transition in the fluoride‐rich phase. Upon isothermal heat treatment, the translucent GCs transform into transparent ones, making UC luminescence even stronger. The enhanced UC luminescence leads to strong temperature‐sensing ability of the studied glasses. The nano‐micro phase separation is clarified by atomistic simulations and scanning electron microscopy. This study implies that phase separation engineering is a powerful way to achieve superior photonic performances.

Multi-target responsive nanoprobe with cellular-level accuracy for spatiotemporally selective photodynamic therapy.

Photodynamic therapy is known for its non-invasiveness to significantly reduce undesired side effects on patients. However, the infiltration and invasiveness of tumor growth are still beyond the specificity of traditional light-controlled photodynamic therapy (PDT), which lacks cellular-level accuracy to tumor cells, possibly leading to "off-target" damage to healthy tissues such as the skin or immune cells infiltrated. Here, upconversion nanoparticles (UCNPs) were co-encapsulated with manganese dioxide (MnO2) by amphiphilic polymers poly(styrene-co-methyl acrylate) (PSMA) and further coated with photosensitizer (riboflavin)-loaded mesoporous silica (C@S/V). The C@S/V nanoprobes exhibited shielded upconversion luminescence in normal conditions (pH 7.4, no hydroperoxide (H2O2)) under 980-nm irradiation and thus minimal reactive oxygen production from riboflavin. However, the excess H2O2 (1mM) and acidic environment (pH 5.5) could decompose the MnO2 within the C@S/V, resulting in remarkable enhancement of upconversion luminescence and a favorable hypoxia-relieving condition for PDT, providing a spatiotemporal signal for therapy initiation. The C@S/V nanoprobes were applied to the co-culture of normal cells (HEK293) and pancreatic cancer cells (Panc02) and performed a selective killing on Panc02 under the 980-nm irradiation. By using the "double-safety" strategy, a responsive C@S/V nanoprobe was designed by the selective activation of acidic and H2O2-rich conditions and 980-nm irradiation for spatiotemporally selective photodynamic therapy with cellular-level accuracy.

Enhancement of upconversion luminescence in Yb3+/Er3+-doped BiVO4 through calcination

Dopant concentration is generally increased in order to enhance the emission efficiency of the upconversion phosphor materials. However, a higher doping concentration generally results in concentration quenching of the upconversion emission resulting in low upconversion efficiency. In such instances, the calcination technique can offer an alternate way of enhancing the emission efficiency of the upconversion phosphors. Here, Yb3+/Er3+-doped BiVO4 has been synthesized by microwave hydrothermal process and the as-synthesized phosphor was calcined at 900 °C in air. Yb3+/Er3+-doped BiVO4 phosphor has been systematically characterized. The elemental distribution is homogeneous. Phase change has occurred from the tetragonal BiVO4 of the as-synthesized sample to the mixture of tetragonal and monoclinic BiVO4 in the calcined sample. The bandgap of the calcined sample has been reduced by 0.52 eV as compared to the as-synthesized one. Under 980 nm excitation, the calcined sample shows ∼ 7 and 15-fold enhancement in the upconversion and downshifting emission intensity, respectively, as compared to the as-synthesized sample. The calcination is found to have increased the lifetime of all the emitting excited states resulting in enhanced emission efficiency which has been confirmed by the time-resolved photoluminescence measurements.

Varying aspect ratios of Au nanorods with LSPR effect for efficient enhanced upconversion luminescence

Varying aspect ratios of Au nanorods with LSPR effect for efficient enhanced upconversion luminescence

Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength.

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light-matter interactions in nanophotonic composite systems and promote UCNP applications.

Enhancing upconversion luminescence of rare earth ions by the activation of the antenna effect in plasmonic cuprous sulfide nanoparticles

To modulate the local electromagnetic field in the upconversion luminescence (UCL) of rare earth ions is one of the most effective ways to improve the luminescence intensity of upconversion nanocrystals (UCNs). Herein, the luminescence intensity of UCNs was increased by 5.8 times by activating the antenna effect of near-infrared plasma in cuprous sulfide nanoparticles. By simulating the local electromagnetic field distribution of the core-shell composites under 980 nm excitation light, the UCL enhancement mechanism of rare earth ions was studied. It showed that the antenna effect of plasmonic cuprous sulfide nanoparticles enhanced the absorption and utilization of excited light by UCNs, and the optical field in the vicinity of the core-shell composites was significantly optimized by inducing the localized surface plasmon resonance coupling between cuprous sulfide nanoparticles. Finally, our results provide a novel way to effectively regulate the local electromagnetic field in the UCL of rare earth ions.

Modulated upconversion luminescence of WO3: Yb3+/Ho3+ through non-equivalence substitution of Bi3+ ions

The upconversion luminescence (UCL) of inorganic materials doped with activators and sensitizers has great application, but its luminescence intensity always impose restrictions on its development. Herein, an obvious enhancement in luminescence intensity of the WO3: Yb3+, Ho3+ phosphor was realized through non-equivalence substitution of Bi3+ ions. The single pure phase of the synthesized WO3: Yb3+, Ho3+, and Bi3+ phosphors has been confirmed by the XRD pattern. The morphology of phosphors and valence state of elements have been performed by SEM and XPS techniques. The sample on excitation with 980 nm performs forceful green emission and weak red emission at 543 nm and 662 nm, separately. The concentrations for doped Yb3+ and Ho3+ to obtain the optimal UCL in WO3 are 8% and 1%, respectively. The optimized doping concentration for Bi3+ ions is 3%. Compared to samples without Bi3+ ions, the Yb3+/Ho3+/Bi3+ doped WO3 obtains 1.59 and 2.33 times increase in emission intensity of green and red, respectively. We also explored the UCL mechanism and enhancement mechanism on the basis of the power dependency, the UCL and the downshift luminescence. These results based on Yb3+/Ho3+ UCL phosphors research is of great significance.