Strong Upconversion Luminescence Research Articles

Strong multi-mode upconversion luminescence of YbVO4: Er3+ phosphors for multimode optical thermometry

This study explored the multi-mode upconversion luminescence in YbVO4: Er3+ under a 980nm laser. The optimal doping concentration of Er3+ ions in YbVO4: Er3+ is 0.02. The phosphor exhibits green (527nm, 2H11/2→4I15/2 and 553nm, 4S3/2→4I15/2), red (654nm, 4F9/2→4I15/2) and near-infrared emissions (803nm, 4I9/2→4I15/2). A multi-mode temperature sensor of YbVO4: Er3+ was developed, featuring three temperature sensing modes based on the luminescent intensity ratio (LIR) of 2H11/2/4S3/2 thermally coupled level, as well as the LIR of 2H11/2/4F9/2 and 4S3/2/4I9/2 non-thermally coupled levels. Corresponding maximum relative sensitivities were determined to be 1.21% K−1 at 298K, 0.93% K−1 at 298K, and 0.33% K−1 at 473K, respectively. The phosphor demonstrates notable temperature sensitivity, highlighting its potential in optical temperature sensing. This study introduces an innovative platform for crafting multi-mode self-reference optical temperature sensors, presenting substantial advancements in the field.

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

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

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

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

Natural and polyanionic heparin polysaccharide functionalized upconversion nanoparticles for highly sensitive and selective ratiometric detection of pesticide

Pesticide contamination is a global concern, threatening human health and food safety. Herein, we developed heparin (HEP) functionalized upconversion nanoparticles (UCNPs)-based ratiometric nanosensor for the sensitive detection of 2,6-dichloro-4-nitroaniline (DCN) pesticide via inner filter effect. The strategy for HEP functionalization of UCNPs is based on adjusting the surface potentials of UCNPs with polyanionic HEP through the electrostatic interaction. UCNPs (NaYbF4:Gd/Y/Tm@NaYbF4@NaYF4) was designed with core-shell-shell structure and extra sensitizer layer for efficient and strong upconversion luminescence (UCL) in the range of UV to NIR. After incorporation of DCN, the upconverted UV emission of UCNPs-HEP ratiometric nanosensor was considerably quenched with the NIR UCL at 800 nm remaining unchanged as internal standard. The UCNPs-HEP ratiometric nanosensor can achieve outstandingly selective and sensitive detection of DCN at the wide linear range of 5–300 μM with a detection limit of 0.41 μM. The remarkable applicability of the UCNPs-HEP ratiometric nanosensor was verified in apple, cucumber and grapes samples. The developed UCNPs-HEP ratiometric nanosensor with excellent biocompatibility and water dispersion capability, is promising for convenient, selective and sensitive sensing of DCN towards food and aqueous samples.

Optical Upconversion in Mononuclear Lanthanide Co-Crystal Assemblies.

In this work, we developed two kinds of co-crystal assemblies systems, consisting of discrete mononuclear Yb3+ and Er3+ and mononuclear Yb3+ and Pr3+, which can achieve Er3+ and Pr3+ upconversion luminescence, respectively, by Yb3+ sensitization under 980 nm excitation. The structure and composition of two co-crystal assemblies were determined by single crystal X-ray diffraction. By investigation of the series of two assemblies, respectively, it is found that the strongest upconversion luminescence is both obtained when the molar ratio of Yb3+ and Ln3+ (Ln=Er or Pr) is 1 : 1. The energy transfer mechanism of Er3+ assemblies is determined as energy transfer upconversion, while that of Pr3+ assemblies is determined as energy transfer upconversion and cooperative sensitization upconversion. This is the first example of Pr3+ upconversion luminescence at the molecular dimension at room temperature, which enriches the research in the field of upconversion luminescence with lanthanide complexes.

Highly efficient upconversion luminescence in narrow-bandgap Y2Mo4O15.

Lanthanide-doped upconversion (UC) materials have been extensively investigated for their unique capability to convert low-energy excitation into high-energy emission. Contrary to previous reports suggesting that efficient UC luminescence (UCL) is exclusively observed in materials with a wide bandgap, we have discovered in this study that Y2Mo4O15:Yb3+/Tm3+ microcrystals, a narrowband material, exhibit highly efficient UC emission. Remarkably, these microcrystals do not display any four- or five-photon UC emission bands. This particular optical phenomenon is independent of the variation in doping ion concentration, temperature, phonon energy, and excitation power density. Combining theoretical calculations and experimental results, we attribute the vanishing emission bands to the strong interaction between the bandgap of the Y2Mo4O15 host matrix (3.37 eV) and the high-energy levels (1I6 and 1D2) of Tm3+ ions. This interaction can effectively catalyze the UC emission process of Tm3+ ions, which leads to Y2Mo4O15:Yb3+/Tm3+ microcrystals possessing very strong UCL intensity. The brightness of these microcrystals outshines commercial UC NaYF4:Yb3+,Er3+ green phosphors by a factor of 10 and is 1.4 times greater than that of UC NaYF4:Yb3+,Tm3+ blue phosphors. Ultimately, Y2Mo4O15:Yb3+/Tm3+ microcrystals, with their distinctive optical characteristics, are being tailored for sophisticated anti-counterfeiting and information encryption applications.

Strong green up-conversion luminescence and optical thermometry of Ho3+/Yb3+ Co-doped AlN submicron towers

Rare-earth (RE) doped aluminum nitride (AlN) holds great promise for integrated optoelectronic devices. Here, the Ho and Yb co-doped AlN (AlN:Ho3+/Yb3+) submicron towers were prepared by a direct nitridation route. XRD, Raman, XPS and EDS studies showed successful doping of Ho and Yb ions into AlN. SEM images show that the submicron towers have an interesting layered structure by layer-by-layer stacking of hexagonal AlN nanosheets. Under excitation at 980 nm, AlN:Ho3+/Yb3+ submicron towers exhibit up-conversion (UC) luminescence at 540, 550, 659, and 762 nm, which are due to Ho3+/Yb3+ system from 5F4, 5S2→5I8, 5F5→5I8, and 5F4, 5S2→5I7 respectively. Based on the intensity ratio and decay lifetime of UC luminescence, the optical temperature sensing characteristics are investigated from 298 K to 548 K. The maximum relative sensitivities associated with the intensity ratio of I540, 550 and I659 and decay lifetime of 659 nm are as high as 2.73% K−1 and 0.43% K−1, respectively. This work broadens the optoelectronic properties of RE doped AlN.

The Use of Diatoms in the Synthesis of New 3D Micro-Nanostructured Composites (SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs) Exhibiting an Intense Anti-Stokes Photoluminescence.

New 3D micro-nanostructured composite materials have been synthesised. These materials comprise SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs, exhibiting strong upconversion luminescence. The synthesis was accomplished by metabolically doping diatom cells with neodymium and vanadium. Subsequently, the biomass of these doped diatoms was subjected to pyrolysis at 800 °C. The morphology, structure, and physicochemical properties of the doped diatom biomass as well as dried (SiO2/CaCO3/Corg/NdVO4NPs) and pyrolysed (SiO2/CaO/Corg/NdVO4NPs) samples were characterised using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), thermal analysis (TG), and fluorescence spectroscopy (FS). Studies have shown that the surface of diatom shells is covered with trigonal prismatic nanocrystallites (nanoparticles) of NdVO4 with dimensions of 30-40 nm, forming the crystallite clusters in the form of single-layer irregular flakes. The synthesised composites produced intense anti-Stokes fluorescent emission in the visible region under xenon lamp excitation in the near-infrared (λex = 800 nm) at room temperature in an ambient atmosphere. Such materials could be attractive for applications in solar spectrum conversion, optical sensing, biosensors, or photocatalysts.

Ultrastrong up-conversion luminescence in inert-active-inert sandwich structure with critical inert-core size

Lanthanide-based up-conversion materials exhibit abundant emission colors under infrared excitation; however, enhancing their up-conversion luminescence efficiency remains a hot topic and a challenge. Here, we show ultra-strong up-conversion luminescence in an inert-active-inert sandwich structure with critical core sizes. It is observed that the emission intensity of the sandwich structure (NaYF4@NaYbF4:0.5 %Tm@ NaYF4) is equal to ∼ 129 times of that in the NaYF4@NaYbF4:0.5 %Tm core/shell nanoparticles and 64 times of that in the NaYbF4:0.5 %Tm@Y core/shell nanoparticles. Moreover, it is more than a tenfold enhancement compared to the well-known classic core–shell structures (NaYF4:20 %Yb, 0.5 %Tm@NaYF4). By restricting the activator to 2D planes, their interactions with vacancies that are randomly distributed in 3D space are minimized. As a result, the energy transfer rate of Yb3+ defects is suppressed in this sandwich structure, while further effectively maintaining or enhancing the energy transfer from Yb3+ to the activator. Worth mentioning is that the strongest up-conversion luminescence is observed in the inert-active-inert sandwich structure with a critical inert core size of approximately 85 nm, which is in good agreement with the inflexion point of the calculated the effective excitation volume per unit cross-section.

Green-emitting lanthanum niobate mesoporous nanospheroids for near-infrared light responsive cancer theranostics

Biomedical applications require nonlinear optical materials with high performance and specific morphology. Among these materials, rare-earth niobates are very promising candidates. However, synthesizing pure-phase rare-earth niobates with controlled shape is challenging. To overcome this obstacle, we present a feasible technique to prepare biocompatible LaNbO4:Er3+/Yb3+ mesoporous nanospheroids with strong upconversion luminescence. We use a pre-Ouzo effect assisted hydrothermal process to obtain the monoclinic phase nanospheroids, which exhibit two-photon excitation induced green emission under 980 nm laser irradiation. We also investigate the energy transfer mechanism between Yb3+ and Er3+ in the LaNbO4 matrix and also explored their pathways in energy level diagram. The cytocompatibility of the LaNbO4:Er3+/Yb3+ mesoporous nanospheroids is verified by Cell Counting Kit-8 assay. Moreover, the cytoplasm and nucleoplasm of LaNbO4:Er3+/Yb3+ mesoporous nanospheroids stained MDA-MB-231 breast cancer cells exhibit upconversion luminescence, indicating that the mesoporous nanospheroids can enter them effectively. Additionally, these nanospheroids have a good ability to deliver DOX to the cancer cells. These results suggest that the LaNbO4:Er3+/Yb3+ mesoporous nanospheroids are promising candidates for luminescence imaging-based cancer diagnosis and therapy.

Preparation and strong green upconversion luminescence of Ca9Y(VO4)7: Yb3+/Er3+ phosphor

Exploring novel oxysalt compounds remains significant due to their affordability and versatile applications, such as serving as laser crystals, piezoelectric crystals, frequency-doubling crystals, and luminescent materials. Specifically, this study introduces a new near-single green upconversion luminescent Ca9(VO4)7: Yb3+/Er3+ material, synthesized through high-temperature solid-phase methods. When subjected to 980 nm near-infrared laser irradiation, the Ca9(VO4)7: 0.3 Yb3+, 0.02 Er3+ phosphor demonstrates robust green luminescence at 531 nm (2H11/2 → 4I15/2) and 558 nm (4S3/2 → 4I15/2), accompanied by faint red luminescence at 665 nm (4F9/2 → 4I15/2). The optimal doping concentrations for Yb3+ and Er3+ ions, yielding the highest upconversion luminescence intensity, are determined to be 0.3 and 0.02, respectively. The investigation elucidates the upconversion luminescence mechanism through the downward shift spectrum in photoluminescence and the pumping power dependence of upconversion green-red luminescence. The primary excitation pathway identified for the upconversion process in Ca9Y(VO4)7: 0.3 Yb3+, 0.02 Er3+ involves Yb3+ (2F5/2) + Er3+ (4I11/2) → Yb3+ (2F7/2) + Er3+ (4F7/2). This research contributes to the exploration of new materials, injecting vitality into modern industries and production processes.

Strong green upconversion emission from submicron spindle-shaped SrMoO4:Yb3+,Er3.

Upconversion luminescence (UCL) is a fluorescence process where two or more lower-energy photons convert into a higher-energy photon. Lanthanide (Ln3+)-doped UCL materials often suffer from weak luminescence, especially when directly synthesized by a hydrothermal (HT) process due to the existing hydroxyl group and undesirable arrangement of dopants within host lattices which quench luminescence and limit energy transfer. Therefore, additional heat treatment processes are required to enhance their UCL emission, even though direct hydrothermal synthesis without further heat treatment has the advantages of low energy consumption, fast synthesis, and wide applicability to generate UCL materials. In this study, via a HT process without annealing, we have produced Yb3+ and Er3+ co-doped SrMoO4 submicron spindles with a strong green UCL emission which can be seen with the naked eye, which HT produced oxide-based UCL materials often fail to demonstrate. We have investigated different HT synthesis conditions, such as temperature, time, pH and dopant composition, which control the nucleation, growth, lattice structure arrangement, and ultimately their UCL properties through XRD, SEM, EDS and UCL measurements. The bright green UCL from the SrMoO4:Yb,Er submicron spindles is further enhanced by post-synthesis annealing within a molten NaNO3/KNO3 system to prevent particle size growth. The green UCL intensity from the annealed SrMoO4:Yb,Er submicron spindles surpasses samples produced by the solid-state method and is comparable to that from the commercial NaYF4:Yb,Er sample. We have further studied the temperature-dependent luminescence of both the HT-prepared and molten-salt annealed SrMoO4:Yb,Er submicron spindle samples. The strong UCL from our SrMoO4:Yb,Er submicron spindles could warrant their candidacy for bioimaging and anticounterfeiting applications.

Structural, luminescence, and temperature sensing properties of the Er3+-doped germanate-tellurite glass by excitation at different wavelengths

Er3+-doped germanate-tellurite glasses were prepared by high-temperature melting method, in which structure, luminescent and, temperature-sensing properties were studied. The Raman spectrum indicates that the maximum phonon energy is low, which is 860 cm−1. The transmission spectrum indicates that the infrared transmissive range of glass is wide, visible, and infrared transmittance is high. Parameters of spectral line intensity Ωλ and radiation parameters were calculated based on Judd-Ofelt theory, which showed that the glass has large values of Ω2 and Ω6, and values of Ω2 and Ω6 decrease with increasing concentration of Er3+ ions. Strong up-conversion luminescence was obtained at 808, 980 and 1550 nmLD with wavelengths at 534, 553 and 668 nm, respectively, and strong down-conversion luminescence of 1.53 and 2.7 μm also were obtained. The up-conversion emission intensity under three-wavelength simultaneous excitation is significantly enhanced compared to monochromatic excitation. The emission intensity corresponding to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transition of Er3+ ions varied with temperature, and the fluorescence intensity ratio FIR of 556 nm and 524 nm increased with increasing temperature. In the temperature range from 330 to 610 K, the maximum sensitivity of glasses was 15.63 × 10−3 K−1 and 19.74 × 10−3 K−1 at T = 570 K, respectively under 808 and 980 nm LD excitation.

Enhanced upconversion luminescence using long-range surface plasmon resonance mode with prism coupler

In the study, we present the significant enhancement of the upconversion luminescence by taking advantage of long-range surface plasmon resonance mode. Compared with the reflection enhanced upconversion luminescence of Ag film, the intensity of upconversion luminescence enhanced by long-range surface plasmon resonance mode is improved 100 times. Additionally, the finite-difference time-domain simulation indicates that the incident light energy can concentrate in the upconversion nanoparticles doped dielectric layer at the long-range surface plasmon resonance mode, which the maximum electric field enhancement factor |E|2/|E0|2 can reach to 58. The experimental result shows that the upconversion luminescence enhancement is related to the thickness of doped Polymethylmethacrylate (PMMA) layer. Furthermore, due to the excited upconversion luminescence having high directionality, it is shown that the strong upconversion luminescence could be received at the specific angle.

High-sensitivity NaYF4:Yb3+/Ho3+/Tm3+ phosphors for optical temperature sensing based on thermally coupled and non-thermally coupled energy levels.

Non-contact optical temperature sensors are highly sought after by researchers due to their satisfactory temperature resolution (δ(T) < 0.1 °C), high relative thermal sensitivity (Sr > 1% °C-1), fast temporal response (t < 0.1 s), and long-term optical stability. In this study, NaYF4:Yb3+/Ho3+/Tm3+ upconversion nanoparticles were prepared by a solvothermal method, and their crystal structure, microscopic morphology, and luminescence mechanism, together with the temperature sensing properties of the specimens, were investigated. Under 980 nm laser excitation, the specimens exhibited strong upconversion luminescence, and the emission peaks corresponded to the characteristic energy level jumps of Ho3+ and Tm3+, respectively. The temperature-dependent luminescence spectra of the samples were investigated based on the fluorescence intensity ratio (FIR) technique over a temperature gradient of 295-495 K. The samples are based on thermally coupled energy levels (TCLs: 1G4(1,2) → 3H6(Tm3+)) and non-thermally coupled energy levels (NTCLs: 3F3 → 3H6(Tm3+) and 5F3 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 1G4 → 3H6(Tm3+), 3F3 → 3H6(Tm3+) and 5F5 → 5I8(Ho3+), 3F3 → 3H6(Tm3+) and 5F4 → 5I8(Ho3+)) for temperature sensing performance. The maximum absolute sensitivity (Sa), relative sensitivity (Sr), and minimum temperature resolution δ(T) were found to be 0.0126 K-1 (495 K), 1.7966% K-1 (345 K), and 0.0167 K, respectively, which are better than those of most sensing materials, and the simultaneous action of multiple coupling energy levels can further improve the temperature precision. This study indicates that the sample has a good value for optical temperature measurement and also provides new ideas for the exploration of other high-quality optical temperature sensing materials.

Synthesis and characteristics of BaYF5:Yb3+, Er3+@BaYF5 nanoparticles as a new near-infrared fluorescence bioimaging probe

Fluorescent bioimaging technology has been widely used in clinic because of its high sensitivity, quick feedback, and no radiation. Among them, NIR-II imaging has lower absorption, tissue scattering, self-fluorescence, and higher signal-to-noise ratio. As a precursor of nanoprobe, BaYF5 is an excellent material due to its low phonon energy, which makes it easy to achieve rare earth ion energy level transition and obtain strong upconversion luminescence. A near-infrared II (NIR-II) rare earth fluoride nanoparticle (NP) BaYF5 : Yb3 + , Er3 + @ BaYF5 has been constructed. The luminescence principle of the material was deeply analyzed, and the influence of different doping ion ratio on fluorescence intensity was explored. Finally, the optimal doping ratio for this matrix material was obtained. In addition, according to the surface properties of the materials, the water solubility and biocompatibility of the NPs were significantly improved by the modification. Our work also systematically tested and analyzed the cytotoxicity, hematotoxicity, and tissue toxicity of the NPs and finally realized the high-resolution fluorescence imaging in living mice. This NP can be used as an effective and safe NIR-II contrastive agent, which provides the possibility for the detection and monitoring of physiological activity under deep tissue in vivo.

Flexible piezoelectric nanogenerator based on the Er3 + doped lead-free (Na0.5Bi0.5)TiO3-BaTiO3 piezoelectric nanofibers with strong upconversion luminescence

Flexible piezoelectric nanogenerators (PENG) have attracted wide attention because of their great potential in solving the power supply problem of wearable electronic devices. In order to expand the applications of PENG, high quality (Na 0.5 Bi 0.5 )TiO 3 -0.06BaTiO 3 (NBT-0.06BT: x Er 3+ ) nanofibers doped with different Er 3+ concentrations were prepared by the gel-sol electrostatic spinning method. The morphology and phase structure of the prepared nanofibers were characterized. Dense nanofibers with good crystallization have been obtained. The local ferroelectric properties of the nanofibers were characterized by PFM. It is found the prepared nanofibers have a strong upconversion (UC) photoluminescence (PL) property. Utilizing the fluorescence intensity ratio (FIR ) technique, the temperature sensing properties of the nanofibers has been investigated, showing a maximum sensitivity of 0.0043 K −1 . Finally, the flexible PENG was prepared by encapsulating NBT-0.06BT:0.01Er 3+ nanofibers, interdigital electrode and PDMS. The maximum voltage output of PENG is 97 V. The present investigation integrates the luminescence characteristics and electrical properties of nanofibers into the flexible PENG, which may greatly expand its application field. • NBT-0.06BT: x Er 3+ nanofibers with high quality have been successfully prepared. • NBT-0.06BT: x Er 3+ nanofibers have excellent temperature sensing properties. • The present PENG has a potential application in optics. • The output voltage of the PENG reaches a high value of 97 V.

Up-conversion luminescence and temperature sensing properties based on Y2GeO5: Er3+, Yb3+ phosphors for three-mode optical thermometry

Herein, a series of novel Y2GeO5: Er3+, Yb3+ phosphors were prepared through traditional high-temperature solid-state reactions under an air atmosphere. During whole experiments, the fluorescence intensity ratio (FIR), crystal structure, up-conversion (UC) luminescence, and energy transmission between Er3+ and Yb3+ of all the samples were combined to explore their properties as optical thermometer. By exciting 980 nm laser, strong UC luminescence of Er3+ ions was emitted at 522, 546, and 652 nm, and by increasing the Er3+, Yb3+ ions co-doped concentration, the UC luminescence intensity of Er3+ ions was greatly enhanced. By using two different techniques, a dual-mode temperature sensor was explored based on the FIR of thermal coupling (2H11/2/4S3/2) and non-thermal coupling (2H11/2/4F9/2) energy levels. And the maximal relative sensitivities of thermal coupling and non-thermal coupling were 1.17%·K−1 and 1.71%·K−1, respectively. In addition, the fluorescence lifetime was used as the third temperature detection signal. And the maximum of relative sensitivity based on fluorescence lifetime was 1.81%·K−1. All the above research shows that Y2GeO5: Er3+, Yb3+ phosphors are prospective applications in temperature sensing.

Synthesis and spectroscopic properties of Er3+/Yb3+-codoped GdNbO4 phosphor for thermometry and marine safety protection

Micron-sized GdNbO4:Er3+/Yb3+ phosphors were prepared by employing a high-temperature solid-state reaction. The crystalline phase, morphology, composition, spectroscopic properties, and impact of rare-earth ion concentration, temperature and high salinity environment were systematically characterized. The extracted results show that phosphor is dominated by the existence of the GdNbO4 crystalline phase. Their morphology and agglomeration phenomenon are strongly dependent on the rare-earth concentration. The phosphor exhibits also excellent up-conversion luminescence (UCL) properties under 980 nm excitation, while a two-photon process accounts for UCL. The following optimal concentrations were selected for enhanced UCL intensity: 10 mol% for Yb3+ and 3 mol% for Er3+. The phosphor shows excellent thermometric performances including strong UCL, good thermal stability, appropriate sensitivity and a wide sensitivity response range. To evaluate the accuracy of the present optical thermometer, the temperature of a heated bench has been comparatively measured by using the proposed optical thermometer and a commercial thermocouple with an accuracy of 1 K. By comparing the temperature values measured by the two methods, it can be concluded that the present optical thermometer has an accuracy better than 1.6 K. In addition, the phosphor exhibits good chemical stability in high salinity environment. Interestingly, its crystalline phase, structure, and UCL spectral structure, intensity and color are all preserved after one-month immersion into a high salinity solution.

Surface modified hexagonal upconversion nanoparticles for the development of competitive assay for biodetection.

Up-conversion nanoparticles (UCNPs) of sodium yttrium fluoride with ytterbium and erbium ions as sensitizer and activator (β-NaYF4/Yb3+/Er3+) have been synthesised by a solvothermal method. The synthesised particles were found to be highly uniform in size (~50nm) and of hexagonal crystal phase producing strong up-conversion luminescence dominated in the green wavelength region. During the synthesis, photoluminescence properties of the reaction mixture were monitored at regular intervals to ensure the required particle size distribution and luminescence efficiency. The hydrophobic particles thus obtained were modified by coating with silica, yielding particles that were stable in aqueous media. The silica coated UCNPs were further modified with maleimide-polyethylene glycol-silane (mal-PEG-silane) to provide thiol reactive surface groups. The silanized, maleimide-bearing UCNPs were effective for conjugating to reductively-cleaved half antibodies against ofloxacin, a veterinary antibiotic, to produce photoluminescent nanobiosensors for its detection and quantification. The speed and minimum detection concentration (~10nM) that we report for a competitive assay of ofloxacin in this study is promising for developing sensors for this and other biomolecules.