UCS Intensity Research Articles

Enhancing Tm3+ upconversion via engineering interfacial strain for selective and sensitive MO sensing

Methyl orange (MO) is a widely used organic dye in industrial chemical production and biomedical research. However, its presence also poses potential risks to the environment and public health. The current MO sensing methods face numerous challenges such as low detection efficiency, expensive equipment, and complex operation. In this study, we propose a detection scheme based on heterostructure upconverting nanocrystals (UCNCs), where BaYF5:20Yb/0.5 Tm@SrYF5 UCNCs function as the energy donor, while the organic molecule methyl orange acts as the electron acceptor to quench the fluorescence emission band. The brightness and UC efficiency of NCs is significantly improved by engineering the interfacial strain. Specifically, the UC intensity of the BaYF5:Yb/Tm@SrYF5 core/shell NCs, exhibited a substantial increase of approximately 425-fold compared to that of the core NCs. The detection limit is measured to be about 0.25 μM, which is better than most reported fluorescence sensors. These results highlight the significant application prospects of fluorescence detection technology in the field of environmental safety.

Enhancing upconversion via constructing local energy clusters in lanthanide-doped fluoride nanoparticles

By introducing local energy clusters within the NaGdF4 lattice, the optimal Er3+, Ho3+ and Tm3+ doping concentrations were increased to 8, 8, and 2 mol%, respectively. The UC intensity was enhanced approximately 54.3 times by doping Ca2+.

Thermally stable upconverting Na3Zr2(SiO4)2PO4: Er3+/Yb3+ phosphors for displays and optical thermometry

The advanced new Er 3+ /Yb 3+ : Na 3 Zr 2 (SiO 4 ) 2 PO 4 (NASICON) monoclinic phosphors prepared by solid state reaction technique has been analyzed as upconverting materials. The crystal phase, structural parameters, surface morphology , different functional groups and bandgap of the synthesized phosphors have been analyzed. Under 980 nm continuous wave diode laser excitation, the codoping of Yb 3+ ions in the Er 3+ doped phosphors exhibit fascinating results. Stark sublevels observed in the upconversion emission have been used for the fluorescence intensity ratio (FIR) based thermometry. Relative & absolute sensitivity, thermal stability and temperature dependent CIE have been determined. The thermally stable Na 3 Zr 2 (SiO 4 ) 2 PO 4 : Er 3+ /Yb 3 phosphors with high color purity can be utilized in sensing, display and security purposes. Upon 980 nm excitation the UC emission obtained from Er 3+ /Yb 3+ doped Na 3 Zr 2 (SiO 4 ) 2 PO 4 phosphors have been utilized for temperature sensing and security ink application. • UC intensity enhancement of ~ 13 times has been observed with incorporation of Yb 3+ in Er 3+ doped Na 3 Zr 2 (SiO 4 ) 2 PO 4 upconverting phosphors. • Maximum absolute and relative sensitivity of the developed phosphor have been found to be 6.4 @ 393 K and 9.3 @ 303 K respectively with thermal resolution± 0.30 K at 303 K. • Thermal stability with activation energy ~ 0.30 eV has been studied upto 508 K.

A dendritic DPA annihilator—syntheses, photophysical properties and application for co-assembling enhanced triplet-triplet annihilation upconversion

A dendritic annihilator D-2 containing 18 peripherical methyl ester units was synthesized by attaching the branches on the phenyl unit of 9,10-diphenylanthracene (DPA). The absorption and emission spectra of D-2 are very similar to the unbranched DPA diacid 5 and the lower branched homolog D-1, while the fluorescence quantum yield increased with the degrees of the branching and was determined to be 86.9% for D-2 in MeOH. D-2 was used as the annihilator for triplet-triplet annihilation upconversion with a Schiff-base Pt(II) complex serving as the sensitizer. It was found that D-2 showed very weak UC emission in MeOH with a UC quantum yield of only 1.4%. Interestingly, the UC emission intensity increased significantly by adding different amounts of water in MeOH, the UC intensity was enhanced by more than 9 fold by adding 40% water into MeOH, and the UC quantum yield was determined to be 10.2% in MeOH with 40% water. A mechanism for the enhancing of UC emission was proposed: When in MeOH, the large molecule size of the dendrimer limited the movability of the acceptor, and the shielding effect of the dendritic branches on the DPA core limited the intimate contacts among DPA cores or between DPA core and the sensitizer. When the water was added, D-2 aggregated to nanoparticles with internal hydrophobic cavities induced by the hydrophobic effect and π-π stacking of DPA core, the sensitizer Pt-1 was captured in the internal hydrophobic cavities, and thus, both the TTET and TTA processes were greatly accelerated which attributed to the enhanced TTA-UC.

Investigation of upconversion luminescence for Tb3+/Yb3+ co-doped CaLnAlO4 (Ln = Y, Gd, La) phosphors

Tb3+/Yb3+ co-doped CaGdAlO4 phosphors were synthesized by a conventional solid-state reaction method. Green UC emission was obtained from the prepared samples under 980 nm excitation via a cooperative energy transfer process. The cooperative energy transfer efficiency from Yb3+ to Tb3+ and the phonon-assisted energy transfer efficiency from Tb3+ to Yb3+ were evaluated to be ~40% and ~1%, respectively. Partial substitution of Gd3+ ions with Y3+ or La3+ ions leads to an increase of UC intensity due to the enhancement of local distortion. The results indicate that the synthesized phosphors may be used to increase the efficiency of perovskite-based photovoltaic cells excited by green light.

Phase evolution, structure, and up‐/down‐conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho, Er, Tm)

AbstractGarnet‐type Li6Ca(La0.97Yb0.02RE0.01)2Nb2O12 (RE = Ho, Er, Tm) new phosphors were successfully synthesized via solid reaction at 900°C for 5 hours, whose course of phase evolution, macroscopic/local crystal structure and up‐/down‐conversion (UC/DC) photoluminescence were clarified. Mechanistic study and materials characterization were attained via XRD, Rietveld refinement, DTA/TG, electron microscopy (FE‐SEM/TEM), and Raman/reflectance/fluorescence spectroscopies. The phosphors were shown to exhibit UC luminescence dominated by a ~ 553 nm green band (5F4/5S2 → 5I8 transition) for Ho3+, a ~ 568 nm green band (4S3/2 → 4I15/2 transition) for Er3+ and a ~ 806 nm near‐infrared band (3H4 → 3H6 transition) for Tm3+ under 978 nm laser excitation, with CIE chromaticity coordinates of around (0.31, 0.68), (0.38, 0.60) and (0.17, 0.24), respectively. Analysis of the pump‐power dependence of UC intensity indicated that all the emissions involve a two‐photon mechanism except for the ~ 486 nm blue emission of Tm3+ (1G4 → 3H6), which requires a three‐photon process. The DC luminescence of these phosphors is featured by dominant bands at ~ 553 nm for Ho3+ (green, 5F4/5S2 → 5I8 transition), ~568 nm for Er3+ (green, 4S3/2 → 4I15/2 transition) and ~ 464 nm for Tm3+ (blue, 1D2 → 3F4 transition). The UC and DC properties were also comparatively discussed.

Splitting upconversion emission and phonon‐assisted population inversion of Ba2Y(BO3)2Cl:Yb3+, Er3+ phosphor

AbstractUpconversion (UC) peak of 4S3/2→4I15/2 transition of Er3+ is close to that of 2H11/2→4I15/2 transition. The UC emission splitting of Er3+ caused by coordination fields of host results in that it is difficult to confirm which transitions (4S3/2→4I15/2 or 2H11/2→4I15/2) are responsible for the splitting UC emission peaks. In this work, the UC luminescence peaks located at 524, 540, 551, 565, 662, 677, and 683 nm were observed in the Ba2Y(BO3)2Cl:Yb3+, Er3+ phosphor upon the 980 nm excitation. The 524 and 540 nm UC emissions intensity were increased, while the 551 and 565 nm UC emissions intensity were decreased with the temperature increasing from 323 to 573 K, which is attributed to the phonon‐assisted population inversion from the 4S3/2 to 2H11/2 level. The temperature dependence of UC emission spectra demonstrated that the 524 and 540 nm UC emissions are from 2H11/2→4I15/2 transition, and 551 and 565 nm UC emissions are from the 4S3/2→4I15/2 transition. Temperature sensing property was characterized by the UC intensity ratio of the 2H11/2→4I15/2 transition to 4S3/2→4I15/2 transition. The Ba2Y(BO3)2Cl:Yb3+,Er3+ phosphor has potential application as the non‐contact temperature sensor.

First‐Principles Calculation of Phase/Size Characteristic in Yb3+/Tm3+/ZnO Upconversion Nanoparticles through Metal Ga3+ Doping

AbstractThe crystal size of upconversion nanoparticles (UCNPs) can be effectively controlled by doping metal ions, which remarkably enhances upconversion luminescence (UCL) intensity and pure color turning. This study investigates phase and size properties of Yb3+/Tm3+/ZnO with various concentrations of Ga3+. In Yb3+/Tm3+/ZnO UCL system, Ga3+‐doping controls the structure (nanocrystal size/phase) of UCNPs and the resulting effect of UCL fluorescence properties. The first principles calculations is used to study variety of the band structure state of density and electronic density of ZnO with different Ga3+ ions. Consequently, it is found that such a series of Yb3+/Tm3+/ZnO nanoparticles doped with x mol% Ga3+ (x= 0, 1, 2, 3 mol%) can increase the electron charge density and decrease the size of nanoparticles, thereby exhibiting greatly enhancement of UC intensity.

Microwave Sol-Gel Derived Ho3+/Yb3+ Co-Doped NaCaGd(MoO4)3 Phosphors and their Upconversion Photoluminescence

NaCaGd(MoO₄)₃:Ho 3+ /Yb 3+ ternary molybdates were successfully synthesized by microwave sol-gel method for the first time. Well-crystallized particles formed after heat-treatment at 900°C for 16 h showed a fine and homogeneous morphology with particle sizes of 3-5 μm. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at the 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The strong 520-nm emission band in the green region corresponds to the 5 S₂/ 5 F₄ → 5 I 8 transition of Ho3+ ions, while the strong 630-nm emission band in the red region appears to be due to the 5 F 5 → 5 I 8 transition of the Ho 3+ ions. The optimal Yb 3+ :Ho 3+ ratio was found at 9:1, as indicated by the composition-dependent quenching effect of Ho 3+ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de LEclairage chromaticity coordinates of the phosphors were evaluated in detail.

A fruitful demonstration in sensors based on upconversion luminescence of Yb3+/Er3+codoped Sb2O3-WO3-Li2O (SWL) glass-ceramic

In this article, erbium and ytterbium doped lithium tungsten antimonate (Yb3+/Er3+:Sb2O3-WO3-Li2O) glass-ceramics (GC) is synthesized and its novel applications in temperature sensing and detection of latent fingerprints is studied. It is also estimated that this material could be useful as a solar cell concentrator. The upconversion emission studies on Yb3+/Er3+:SWL glass-ceramics have shown intense green emission at 525 nm (2H11/2 → 4I15/2) & 545 nm (4s3/2 → 4I15/2). The variation of UC intensities with external temperature have shown a well-fashioned pattern, which suggests that the 2H11/2 and 4S3/2 levels of Er3+ ion are thermally coupled and can act as a temperature sensor in the 300–500 K temperature range. Dry powder of Yb3+/Er3+:SWL glass-ceramic is used to develop latent fingerprint with high contrast in green color on glass slide.

Synthesis of NaCaLa(MoO4)3:Ho3+/Yb3+ Phosphors via Microwave Sol-Gel Route and Their Upconversion Photoluminescence Properties

NaCaLa1-x(MoO4)3:Ho3+/Yb3+ ternary molybdates with proper doping concentrations of Ho3+ and Yb3+ (x = Ho3+ +Yb3+, Ho3+ = 0.05 and Yb3+ = 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by microwave sol-gel method. Well-crystallized particles formed after heat-treatment at 900 oC for 16 h showed a fine and homogeneous morphology with particle sizes of 3-5 μm. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The optimal Yb3+:Ho3+ ratios were obtained at 9:1 and 10:1, as indicated by the compositiondependent quenching effect of the Ho3+ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

Promote the threshold of Tm3+ concentration using an inert-core/active-shell structure

The upper limit of Tm3+ doping concentration increases from the well accepted 0.5% to 3% in NaGdF4@Yb/Tm:NaGdF4 NCs with an inert-core/active-shell structure, and the UC intensity increases about 6 times, benefiting from the enhanced energy transfer efficiency from the Yb3+ to Tm3+ ions by confining them in a two-dimensional space.

Microwave sol-gel process of KGd(WO4)2:Ho3+/Yb3 phosphors and their upconversion photoluminescence properties

Double tungstate KGd1−x(WO4)2:Ho3+/Yb3+ phosphors with doping concentrations of Ho3+ and Yb3+ (x=Ho3++Yb3+, Ho3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) were successfully synthesized by the microwave sol–gel method, and the upconversion mechanisms were investigated in detail. The synthesized particles formed after heat-treatment at 900°C for 16h showed a well crystallized morphology with particle sizes of 2–5μm. Under excitation at 980nm, the UC intensities of KGd0.7(WO4)2:Ho0.1Yb0.2 and KGd0.5(WO4)2Ho0.05Yb0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the 5S2/5F4→5I8 and 5F5→5I8 transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 764, 812, 904, 984, 1050, 1106, 1250 and 1340cm−1 induced by the disorder of the [WO4]2− groups with the incorporation of the Ho3+ and Yb3+ elements into the crystal lattice or by a new phase formation.

Microwave-modified sol-gel process of NaY(WO4)2: Ho3+/Yb3+ phosphors and the upconversion of their photoluminescence properties

NaY1−x(WO4)2:Ho3+/Yb3+ phosphors with doping concentrations of Ho3+ and Yb3+ (x=Ho3++Yb3+, Ho3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) were successfully synthesized by the microwave-modified sol-gel method, and the upconversion of their photoluminescence properties was investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 2–5μm. Under excitation at 980nm, the UC intensities of NaY0.7(WO4)2:Ho0.1Yb0.2 and NaY0.5(WO4)2 Ho0.05Yb0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the 4S2/5F4→5I8 and 5F5→5I8 transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong disordered peaks at higher frequencies and weak peaks at lower frequencies induced by the incorporation of the Ho3+ and Yb3+ elements into the Y3+ site in the crystal lattice, which resulted in the unit cell shrinkage accompanying the new phase formation of the [WO4]2− groups.

Countering Fear Renewal: Changes in the UCS Representation Generalize Across Contexts

After treatment of anxiety disorders, fear often returns. Analogue studies show that outside the extinction context the conditional stimulus (CS) activates the acquisition memory (CS predicts unconditional stimulus; UCS), rather than the extinction memory (CS does not predict UCS). Conditioning theory postulates that fear also diminishes after a reduction in the subjective cost of the UCS, which can occur in absence of any changes in the CS-UCS association. We hypothesized that fear reduction via "UCS deflation" generalizes across context. Healthy students underwent acquisition in context A with neutral CSs and 100dB white noise as UCS. One group received post-conditioning UCS exposure, in which UCS intensity decreased over time ("ABAdefl"). Another group received UCS presentations at equal intensity ("ABActrl"). Two groups did a filler task ("ABB"; "ABA"). Then, all groups underwent extinction in context B and were retested in context A (ABA-groups) or B (ABB-group). During each CS participants rated UCS expectancy and UCS cost. Results showed the typical increase in UCS expectancy following the context switch from extinction to test phase. In contrast, UCS deflation caused a reduction in cost ratings that was maintained after the context change. Findings suggest that UCS deflation techniques may reduce fear renewal.

Cyclic MAM Synthesis of CaMoO<sub>4</sub>:Er<sup>3+</sup>/Yb<sup>3+ </sup>Particles and their Upconversion Photoluminescence Properties

Er3+doped CaMoO4(CaMoO4:Er3+) and Er3+/Yb3+co-doped CaMoO4(CaMoO4:Er3+/Yb3+) particles was successfully synthesized by a cyclic microwave-assisted metathetic (MAM) method, followed by heat-treatment. Well-crystallized UC CaMoO4:Er3+/Yb3+particles formed after heat-treatment at 600°C for 3 h showed a fine and homogeneous morphology with particle sizes of 1-3 μm. At excitation at 980 nm, CaMoO4:Er3+/Yb3+particles exhibited a strong 525-nm emission band and a weak 550-nm emission band in the green region, and a weak 655-nm emission band in the red region. The UC intensities of CaMoO4:Er3+/Yb3+particles were much higher than that of the CaMoO4:Er3+particles. The Raman spectra of CaMoO4:Er3+and CaMoO4:Er3+/Yb3+particles indicated the appearance of additional strong peaks in comparision with that of pure CaMoO4.

A single-step synthesis and the kinetic mechanism for monodisperse and hexagonal-phaseNaYF4:Yb, Er upconversion nanophosphors

A single-step synthesis for monodisperse and hexagonal-phase (β)NaYF4:Yb, Er upconversion nanophosphors (UCNPs) with a consistent hexagonalprism shape in the size range from 18 to 200 nm was achieved. The kineticmechanisms for the particle phase transition and growth were examined. Theβ-UCNPs were obtained via co-thermolysis of trifluoroacetate precursors in octadecene(ODE) with combined ligands of oleic acid (OA) and trioctylphosphine (TOP). Theexperimental results showed that the combined OA–TOP ligand was crucial for changingthe surface energy and controlling the particle shape over a broad size range. It wasfound that the particle sizes could be controlled by varying the molar ratios ofNa(CF3COO)/Re(CF3COO)3 (Re = Y, Yb, andEr). A high Na/Re ratio accelerated the cubic-phase transition and promoted the growth of smallerβ-UCNPs. Theformation of β-UCNPs was classified into kinetic and diffusion controlled stages, depending on the reactiontemperature and the dominant crystalline phases formed in each stage. In stage I, 250–310 °C, NaF generation wasthe limiting step and α-UCNPs were formed via a ‘burst of nucleation’. In stage II, above310 °C,the α-UCNPs formed were re-dissolved and the growth ofβ-UCNPs was a diffusion controlled process governed by the Gibbs–Thompsoneffect. A quasi-steady-state species assumption for NaF and a chemical potentialequilibrium in the solution were introduced to explain the particle size dependence onNa/Re ratios. The study of UC luminescence showed that the UC intensity was proportional to the sizes ofthe β-UCNPs.

Sodium pentobarbital: sensory and associative effects in classical conditioning of the rabbit nictitating membrane response.

Four experiments were conducted to determine the effects of sodium pentobarbital (0, 3, 9, and 15 mg/kg) on the acquisition of the rabbit's classically conditioned nictitating membrane response (NMR) and to determine the locus of the drug's effects on sensory, motor, associative, and nonassociative processes. In experiment 1, classical conditioning of the NMR was accomplished by pairing tone and light conditioned stimuli (CSs) with paraorbital shock as the unconditioned stimulus (US). The experiment revealed that pentobarbital retarded the acquisition of conditioned responses (CRs) to both tone and light CSs. Experiment 2, employing unpaired CS, UCS presentations, indicated small but significant drug effects on NMR base rate and nonassociative NMRs to the CS. Experiment 3 revealed no significant drug effect on the psychophysical functions relating UCS intensity to UCR frequency or amplitude, nor on the UCS intensity threshold for eliciting UCRs. On the other hand, in experiment 4, the drug significantly impaired CR frequency over an extended range of CS intensities and raised CS intensity threshold. It was concluded that pentobarbital's attenuation of CS intensity also operated to impair CR acquisition.

Effects of LSD on classical conditioning as a function of CS-UCS interval: relationship to reflex facilitation.

Classical conditioning of the rabbit nictitating membrane response was accomplished by presenting a 100-msec tone CS at intervals 0, 100, 200, 400 and 800 msec before the presentation of a 100-msec shock UCS. In addition, tone-alone trials were used to monitor CR acquisition and shock-alone trials to measure facilitation of the nictitating membrane reflex by the tone CS at the various CS-UCS intervals. LSD at a dose of 13 micrograms/kg (30 nmol/kg) increased the excitatory effects of the shock UCS as measured by a greater frequency and amplitude of UCRs elicited across a wide range of UCS intensities and by the ability of a low intensity shock to produce reflex facilitation. Consequently, LSD produced a higher amplitude of UCRs on UCS-alone trials and on paired trials across all CS-UCS intervals during measurement of tone-induced reflex facilitation. LSD also enhanced CR acquisition across all CS-UCS intervals. Because LSD produced larger amplitude reference UCRs on the UCS-alone trials as compared with controls, calculations of reflex facilitation as a percentage change from these reference amplitudes led to an artifactually smaller effect for the LSD group as compared with controls. Nevertheless, both reflex facilitation as measured prior to CR acquisition on the first day of conditioning and CR acquisition across 10 conditioning sessions were a function of CS-UCS intervals and these two measures were highly correlated in the LSD (+0.94) and vehicle control (+0.85) groups. It was concluded that LSD enhances CR acquisition by enhancing the excitatory effects of both the CS and UCS and thus increasing their ability to enter into associative learning.

The influence of context and UCS intensity on the UCS preexposure effect in a flavor aversion paradigm

Three studies were conducted to evaluate the influence of environmental context and UCS preexposure intensity on the acquisition of a flavor aversion. In the first study, rats were exposed to two UCS-alone presentations at one of three dose levels of LiCl. The rats were given the two UCS preexposures in one of two contexts (familiar or novel). Following the UCS-alone treatment, all of the subjects received two pairings of sucrose and LiCl (1.25 meq) in the familiar context. Animals receiving UCS preexposures in the same context as used during conditioning consumed significantly more sucrose than did saline control animals. In contrast, the influence of prior UCS preexposure was not evident when UCS preexposure was experienced in a context different from that experienced during conditioning. In Experiment 2, all animal received UCS preexposure and conditioning in the novel room. Animals received either two or four preexposures at 0, 1.25, or 3.75 meq dose of LiCl. Two UCS preexposures at 3.75 meq dose produced a stronger UCS preexposure effect than did the 1.25 meq dose. Animals in Experiment 3 received two exposures to either 0-, 1.25-, or 3.75-meq LiCl in one of two contexts, followed by conditioning with the 1.25-meq LiCl dose in the same context as preexposure. Greater UCS interference occurred in animals preexposed to LiCl in the novel rather than familiar environment, with no specific dose effects in either context. These observations are discussed in terms of context blocking and generalization decrement models of the UCS preexposure effect.