Green Upconversion Research Articles

Simple express precursor synthesis of erbium-doped yttrium oxide luminescent material for optical thermometry

A new, simple and inexpensive method for the preparation of nanosized (Y1-xErx)2O3 oxides, including the stages of synthesis and thermolysis of Y1-xErx(HCOO)3 precursors, has been developed. The precursors were obtained by the interaction of mixtures of yttrium and erbium nitrates with formic acid. The effect of erbium concentration on the structure, morphology, and optical properties of (Y1-xErx)2O3 oxides was studied using X-ray diffraction, scanning electron microscopy, and optical absorption methods. Under UV excitation (Y1-xErx)2O3 oxides with 0.005≤x ≤ 0.25 exhibit strong green luminescence related to the 2H11/2/4S3/2 → 4I15/2 transitions and weak red luminescence associated with the 4F9/2 → 4I15/2 transition. According to the CIE chromaticity coordinates, the oxides demonstrate a yellowish-green color emission. A noticeable decrease in the luminescence intensity was recorded for oxides with erbium concentrations above 2.5 mol.% (x = 0.025). Yellowish-green and yellow green upconversion emission resulting from the 4S3/2 → 4I15/2 and the 4F9/2 → 4I15/2 transitions of Er3+ ions were observed upon continuous 980 nm diode laser excitation. When the concentration of erbium in (Y1-xErx)2O3 oxides increases, the luminescence color changes and the intensity of upconversion emission rises. The maximum intensity of upconversion emission was observed for the (Y0.9Er0.1)2O3 oxide. A two-photon upconversion mechanism was established based on the pumping power dependence of UC luminescence intensity. The thermoluminescence characteristics of (Y0.9Er0.1)2O3 oxides based on the ratio of the intensities of the lines corresponding to thermal-coupled 2H11/2 and 4S3/2 levels were determined, the absolute and relative sensitivity values was calculated, and the prospects for using this oxide in non-contact optical thermometers were estimated.

Fluorescent sensing probe based on heterovalent doped Lu2W2.5Mo0.5O12:Er3+/Yb3+ phosphor for real-time chip temperature monitoring

The influence of Li+/Zn2+ heterovalent doping on the structural change and upconversion luminescence properties of Lu2W2.5Mo0.5O12:Er3+/Yb3+ phosphors was investigated in details. The gradual substitution of Li+/Zn2+ ions for Lu3+ ions result in the evolution from orthorhombic Lu2W2.5Mo0.5O12 to monoclinic (LiZn)2W2.5Mo0.5O12, which bring the structural distortion, the reduction of local symmetry and the crystallite growth. The green upconversion intensity of Er3+ ions at 536 nm and 550 nm were enhanced significantly by a factor of 8000 and 4000. The temperature sensing characteristics of a single (LiZn)2W2.5Mo0.5O12:Er3+/Yb3+ particle in all-fiber structure was explored and the unusual thermally-enhanced upconversion luminescence was observed, which is beneficial for achieving high-precision temperature measurement based on the fluorescence intensity ratio technology. The absolute temperature sensitivity reached a maximum of 0.0095 K−1 at 423 K and the temperature deviation was less than 0.6 K. The as-built all-fiber temperature sensor was successfully applied in the on-line monitoring of CPU temperature.

Synergistic red dominancy over green upconversion studies in PbZrTiO3: Er3+/Yb3+ phosphor synthesized via two different modified technique and flexible thin-film thermometer demonstration on C1: PbZrTiO3 @PDMS substrates

Owing to its efficient wide range sensing using a noncontact mechanism with a decimal accuracy level, quick, non-invasive temperature sensors utilizing upconversion (UC) phosphor were examined. These sensors are perfect for cutting-edge applications such as measuring the intracellular temperature and identifying microelectronic issues. It may be possible to modify the performance of phosphor temperature sensors through nanoscale engineering. Despite were potential, it has been discovered that modern nanothermometers are ineffective in maintaining stability over a wide temperature range. Motivated by previous studies on efficient UC based solar cell demonstrations of Er3+/Yb3+: PbZrTiO3 (lead zirconate titanate) phosphors, the UC properties of Er3+/Yb3+: PbZrTiO3 for a wide range of temperature sensing and practical thermometer applications have been investigated. The UC emission properties of the Er3+/Yb3+: PbZrTiO3 phosphors synthesized via different routes, with the same dopant concentration, were compared. We have also investigated the formation of two different crystal symmetry, and an approach for the fine-tuning of the emission from the green to the red region upon changing the synthesis technique. The strategy of choosing an optimized synthesis route, based upon structural investigations, could be a way forward where dopant modification in phosphors is ruled out. Based on the UC optimization, the green and red dominant phosphors under 980 nm excitation with different pulse widths and power densities or at different temperatures were studied; the possible mechanisms were discussed in detail. The sensitivity of Er3+/Yb3+: PbZrTiO3 was independent of the pumping laser characteristics since it was essentially consistent when utilising both continuous wave and laser pulse width modulation or varying power densities. To assess the temperature of the microelectronic components, a flexible thin-film thermometer was made of Er3+/Yb3+: PbZrTiO3 on a polyDiMethylSiloxane substrate. This thermometer shows great repeatability and can measure the temperature of an electronic circuit board correctly. The findings suggested that the current non-contact UC temperature sensor might potentially replace conventional thermometers because of its steady green emission over a wide temperature range (313–673 K) and thermometric sensitivity.

Upconversion luminescence and temperature sensing performance of Er3+ ions doped self-activated KYb(MoO4)2 phosphors

In this work, a series of self-activated KYb(MoO4)2 phosphors with various x at% Er3+ doping concentrations (x = 0.5, 1, 3, 5, 8, 10, 15) was synthesized by the solid-state reaction method. The phase structure of the as-prepared samples was analyzed by X-ray diffraction (XRD), XRD Rietveld refinement and Fourier transform infrared (FT-IR) spectroscopy. The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er3+ doping concentration up to 15 at%. High-purity upconversion (UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er3+ ions in the self-activated KYb(MoO4)2 host is revealed as 3 at%. The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra. In addition, the fluorescence intensity ratios (FIRs) of the two thermally-coupled energy levels, namely 2H11/2 and 4S3/2, of Er3+ ions were investigated in the temperature region 300–570 K to evaluate the optical temperature sensor behavior of the sample. The maximum relative sensitivity (SR) is determined to be 0.0069 K−1 at 300 K and the absolute sensitivity (SA) is determined to be 0.0126 K−1 at 300 K. The SA of self-activated KYb(MoO4)2:Er3+ is almost twice that of traditional KY(MoO4)2:Er3+/Yb3+ codoping phosphor. The results demonstrate that Er3+ ions doped self-activated KYb(MoO4)2 phosphor has promising application in visible display, trademark security and optical temperature sensors.

Polymorphism and up-conversion photoluminescence properties of Y2WO6 doped with Yb3+/Er3+ under excitation at 975 nm

This article reports the synthesis and luminescent properties (up-conversion and down-shifting) of the tetragonal and orthorhombic polymorphs of Y2WO6 doped with Erbium (Er3+) and Ytterbium (Yb3+) cations. The syntheses were carried out by a high temperature solid state reaction. The orthorhombic phase was prepared by pressing the parent compounds into pellets of 13 mm diameter. The samples were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Luminescence up-conversion measurements were analyzed using a tunable continuous wave (CW) Ti:sapphire laser system tuned at 975 nm. The results show that the green up-conversion emission is more intense than the red one in both polymorphs. To gain further clarity on this matter, we have also conducted a study on down-shifting emission spectra measured at 378 nm, where only the strong green emission is observed. The pump power dependence and the decay curves of the (4S3/2 → 4I15/2) transition were also evaluated.

Enhanced upconversion luminescence and single-band red emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor through doping Cu2+

This study reports on a single-band red upconversion emission of Er3+ in a pure-phase β-Ba2ScAlO5: Yb3+/Er3+ fluorescent powder by doping Cu2+. The optimum concentration of Cu2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ powder was 0.20. The red and green emission intensity of β-Ba2ScAlO5: Yb3+/Er3+ sample with optimum concentration of Cu2+ ions increased by 19.1 and 3.6 times, respectively, relative to the β-Ba2ScAlO5:Yb3+/Er3+ material lacking Cu2+ ions. The red-green integral intensity ratio of the β-Ba2ScAlO5:Yb3+/Er3+/Cu2+ phosphor reached 141.9. The potential upconversion luminescence (UCL) mechanism was explored by analyzing the down-shift luminescence (DS) spectra, upconversion luminescence spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Cu2+ triple-doped β-Ba2ScAlO5. Enhanced red emission and green upconversion emission are achieved by energy transfer between defect band by the oxygen vacancy and Er3+ energy levels. This study's findings establish the foundation for developing novel phosphors with single UC red light emission, which has potential applications in illumination displays, optical thermometry, and biomedicine.

An Integrated Temperature-Feedback Photothermal Therapy Platform Based on Dual-Functional Rare Earth-Doped NaSrGd(MoO4)3 Phosphors

Nd3+ doped and Er3+/Yb3+ codoped NaSrGd(MoO4)3 (NSGM) phosphors were synthesized and used to build an integrated temperature-feedback photothermal therapy platform. Intense green upconversion emissions were observed in Er3+/Yb3+-codoped NSGM phosphors and used to construct an all-fiber temperature sensing probe. The temperature dependent fluorescence intensity ratio (FIR) calibration curve was established and the absolute temperature sensitivity Sa reached the maximum value of 0.013 K–1 at 423 K. The photothermal conversion performance of NSGM:Nd3+ phosphors could be easily modified by altering Nd3+ doping concentration and 808 nm laser irradiation power. An integrated all-fiber photothermal temperature measurement platform was built and the temperature measurement error was smaller than ±1 K, which could simultaneously achieve photothermal conversion and temperature measurement in narrow spaces and was expected to be used in local photothermal therapy applications.

Inhibiting oxygen vacancies and twisting NbO6 octahedron in erbium modified KNN-based multifunctional ceramics

It is a challenge to obtain highly tunable multifunctional performances in one ferroelectric system by a simple approach to meet the miniaturization, integration, and functionalization requirements of advanced electronic components. Herein, rare earth erbium (Er) modulated 0.9K0.5Na0.5NbO3-0.1Sr(1-x)ErxTi(1-x/4)O3, (0.9KNN-0.1ST: xEr) transparent-photoluminescent-ferroelectric energy storage multifunctional ceramics are prepared to solve this problem. The effect of lattice distortion and oxygen vacancies by Er doping on the optical and electrical properties is systematically investigated. The Er3+ ions can introduce a large distortion of the NbO6 octahedron by replacing the A-site in KNN-based ceramics. Thanks to the higher c/a ratio and lower oxygen vacancy content are simultaneously obtained in 0.9KNN-0.1ST: 0.1Er ceramics. The effective energy storage density (Wrec) of 0.86 J/cm3, excellent near-infrared transmittance of 51.7% (1 100 nm) and strong green upconversion photoluminescence are achieved in this multifunctional ceramic. This study provides a solid basis for rare earth ions doped ferroelectric ceramics with tunable multifunctional properties and has significant potential for applications in optoelectronic devices.

Intense green upconversion in core-shell structured NaYF4:Er,Yb@SiO2 microparticles for anti-counterfeiting printing

Rare-earth-doped NaYF4 nanoparticles are considered crucial upconversion luminescent materials with many applications, including anti-counterfeiting printing, biological imaging, and optical information storage. This work presents progress in obtaining hydrophilic pigments based on NaYF4:Er,Yb@SiO2 nanoparticles, and their utilization in water-based ink printing for anti-counterfeiting applications. Coating NaYF4:Yb/Er microparticles with SiO2 shells can provide several benefits for printing purposes, such as improved stability, dispersion, and ease of printing. The hydrophilic core-shell structured β-NaYF4:Er, Yb@SiO2 microparticles were successfully prepared using the hydrothermal synthesis and sol-gel Stober method. The obtained microparticles were characterized by Scanning Electron Microscopy, X-ray diffraction, and Energy-dispersive X-ray spectroscopy. Such characterizations confirm that the Er3+ and Yb3+ ions are incorporated in NaYF4 cores, the NaYF4:Er, Yb cores are in hundreds of nanometer sizes, and the NaYF4:Er, Yb microparticles are coated by a silica layer of 50 nm thick. Both NaYF4:Er, Yb and NaYF4:Er, Yb@SiO2 behave as up-conversion luminescent microparticles for both green and red emissions. The CIE chromaticity coordinates indicate that both the nanoparticles have their greenish color under excitation at 980 nm. Although decorating the NaYF4:Er, Yb nanoparticles with the SiO2 shell decreases luminescent intensity (by a factor of 2), this step is still necessary to achieve hydrophilic surfaces for preparing water-based printing inks. Using the synthesized NaYF4:Er, Yb@SiO2 as a pigment, a new water-based ink formula was created based on Polyamide as a polymer matrix. The obtained ink is printable on paper and on transparent and flexible Polyethylene substrate. The printed patterns with a height of 2 cm and a width of 2.5 cm were observed clearly under the irradiation of a 980 nm LED. Their durability in terms of sharpness and color was also assessed after six months.

Activating ultralow upconversion nanothermometry in neodymium sublattice for heart tissue imaging rapid-responsive

The fields of biosensitivity and biological imaging have received a lot of attention from rare earth-doped upconversion nanoparticles (UCNPs). However, owing to the relatively large energy difference of rare earth ions, biological sensitivity based on UCNPs is restricted to detect at low temperature. Here, we design core-shell-shell NaErF4:Yb@Nd2O3@SiO2 UCNPs as a dual-mode bioprobe that produces blue, green, and red multi-color upconversion emissions at extremely low temperatures between 100 K and 280 K. Based on the thermally coupled energy levels (TCELs) of Er3+ (2H11/2 and 4S3/2) and Nd3+ (4F5/2 and 4F3/2) at 100 K, the greatest relative sensitivity (SR) approaches 12.7% K−1. NaErF4:Yb@Nd2O3@SiO2 injection is used to achieve blue upconversion emission imaging of frozen heart tissue, showing that this UCNP can serve as a low-temperature sensitive biological fluorescence.

Structure, morphology, photonconversion and energy transfer characteristics of Er3+/Yb3+:BaYF5 nanocrystals synthesized by hydrothermal method for photovoltaics

Lanthanide doped nanocrystalline fluoride optical materials have been explored for diverse applications in the solar energy harvesting, industry, medical, forensic and biological fields because of high photoluminescence quantum yield and low phonon energy. In this manuscript, Er3+/Yb3+:BaYF5 nanocrystals were synthesized by hydrothermal process. These nanocrystals were investigated through X-ray diffraction (XRD), SEM/TEM, Raman, quantum yield, photoluminescence upconversion (UC) and downconversion (DC) studies. XRD patterns exhibited the cubic phase and no phase deviation with the addition of Er3+ and Yb3+ ions. The TEM images illustrate the cubic-like morphologies of the obtained nanocrystals. Raman spectrum unveils the characteristic vibrational bands with an intense band at 498 cm−1, which is considered the phonon energy of the BaYF5 matrix. Under 488 nm excitation, the near infrared (NIR) emission of Er3+ increases up to 5 mol% and then decreases for a 10 mol% doped sample. Photoluminescence DC quantum yield of Er3+/Yb3+:BaYF5 sample is measured by using integrating sphere in the visible region under 488 nm (Xe flash lamp) excitation, is 4.25%. Under 900 nm laser excitation, intense NIR emissions at 978 and 1550 nm corresponding to Yb3+ (2F5/2 → 2F7/2) and Er3+ (4I13/2 → 4I15/2) ions, respectively, were observed. With the increase of Yb3+ concentration, the NIR emissions of both Er3+ and Yb3+ increase to 5 mol% and then decrease to 10 mol%. The strength of green UC emission of Er3+ decreases with increase of Er3+ concentration, whereas it enhances with the rise of Yb3+ concentration under 980 nm laser excitation. Two-photon UC process is confirmed as the slopes of the green, and red intensities are 2 and 2. These nanocrystals exhibit intense UC and DC emissions under 980 nm and 480 nm, respectively, which can be suitable for improving the efficiency of solar cells.

Upconversion Luminescence Response of a Single YVO4:Yb, Er Particle.

We present the results of the luminescence response studies of a single YVO4:Yb, Er particle of 1-µm size. Yttrium vanadate nanoparticles are well-known for their low sensitivity to surface quenchers in water solutions which makes them of special interest for biological applications. First, YVO4:Yb, Er nanoparticles (in the size range from 0.05 µm up to 2 µm), using the hydrothermal method, were synthesized. Nanoparticles deposited and dried on a glass surface exhibited bright green upconversion luminescence. By means of an atomic-force microscope, a 60 × 60 µm2 square of a glass surface was cleaned from any noticeable contaminants (more than 10 nm in size) and a single particle of 1-µm size was selected and placed in the middle. Confocal microscopy revealed a significant difference between the collective luminescent response of an ensemble of synthesized nanoparticles (in the form of a dry powder) and that of a single particle. In particular, a pronounced polarization of the upconversion luminescence from a single particle was observed. Luminescence dependences on the laser power are quite different for the single particle and the large ensemble of nanoparticles as well. These facts attest to the notion that upconversion properties of single particles are highly individual. This implies that to use an upconversion particle as a single sensor of the local parameters of a medium, the additional studying and calibration of its individual photophysical properties are essential.

Rare earth ions doped Bi2MoO6 luminescent materials: Pechini sol-gel synthesis, down-conversion and up-conversion multicolor emissions, and potential applications

A series of rare earth ions (Eu3+, Sm3+, Yb3+/Er3+, Yb3+/Ho3+, Yb3+/Tm3+) doped bismuth molybdate (Bi2MoO6) phosphors with excellent multicolor luminescence have been synthesized by a facile Pechini sol-gel method. XRD, EDX, and XPS results confirm the highly crystalline orthorhombic phase of Bi2MoO6 and verify that the rare earth ions (RE3+) are effectively integrated into the Bi2MoO6 matrix. During the synthesis process, the calcination conditions play an important role in obtaining the luminescent host matrix, and the optimal calcination condition for the Bi2MoO6 products is determined of 800 °C for 2 h. The Eu3+ and Sm3+ doped Bi2MoO6 samples display intense red and orange-red light under UV/visible excitation whereas the Yb3+/Ln3+ (Ln = Er, Ho, and Tm) doped Bi2MoO6 materials emit green, green, and blue colors when excited by NIR light. Both down-conversion (DC) and up-conversion (UC) multicolor luminescence are obtained by doping the proper Ln3+ activators into the Bi2MoO6 host. The doping concentrations of various RE3+ ions are optimized to generate advantageous phosphors and the luminescence mechanisms of RE3+ ions are systematically studied. The LED devices fabricated by Bi2MoO6:Yb3+/Ln3+ UC phosphors exhibit dazzling multicolor emissions under an injection current, which directly discloses that the as-prepared materials may be of great potential in LEDs and optoelectronic devices. Interestingly, the Bi2MoO6:Yb3+/Er3+/Eu3+ phosphors can simultaneously exhibit red and yellow-green DC emissions and green UC light under excitation of 464, 488, and 980 nm. The multi-mode emission features illustrate that the as-synthesized phosphors may have application prospects in anti-counterfeiting applications.

Enhanced green up/down-conversion emissions through phase transformation in Ho3+/Yb3+ co-doped Y2O3:ZrO2 phosphors in presence of Na+ ions

This study reports the intense green upconversion and downconversion emissions from Ho3+/Yb3+/Na+ co-doped Y2O3:ZrO2 phosphor prepared by traditional solid-state reaction technique for fixed concentration of Ho3+/Yb3+ ions and different concentrations of Na+ ion. The phosphor samples exhibit a multiphase crystalline structure in the absence of Na+ ions. However, with co-doping of Na+ ions (at 20 mol%), it almost turns into Y4Zr3O12 with single rhombohedral phase. When Na + ions are present in the sample, the SEM image reveals a growth in particle size. The UV–Vis–NIR measurements show an enhancement in the absorbance of doped REs ions (Ho3+/Yb3+) on Na+ co-doping. The Ho3+/Yb3+ co-doped Y2O3:ZrO2 phosphor shows an intense green upconversion (UC) emission at 549 nm due to Ho3+ ions on the excitation with 980 nm radiation. In the presence of Na + ions, a modification of the crystallinity, growth in crystallite size (particle size) and an increase in the asymmetry of the crystalline structure around the REs ions led to an enhancement in the intensity of the UC emission almost about ∼8.5 times. The Log-Log plot demonstrates the involvement of two photons in the UC process. The lifetime of the 5F4/5S2 level decreases with increasing the concentration of Na + ion. Thus, the prepared phosphor could be an excellent candidate for source of green light, finger printing, optoelectronic devices etc.

Experimental optimization design synthesis and up-conversion luminescence properties of YNbO4:Ho3+/Yb3+

In order to obtain the maximum green up-conversion luminescence intensity of Ho3+/Yb3+ co-doped YNbO4, a uniform design and a quadratic general rotation combination design were applied to optimize the doping concentration. The concentration of the rare earth corresponding to the strongest green luminescence intensity was determined to be 10% Ho3+/34.9% Yb3+. Maximum luminous intensity of green light tested under 980 nm excitation was 157373.266, which was close to the theoretical calculated integral intensity value of 157290.825. The variation of the up-conversion luminescence spectra at different power density of the 980 nm laser was characterized. According to the formula fitting, the up-conversion luminescence process is a two-photon process. Meanwhile, the temperature sensing characteristic of the samples has been discussed. Finally, the CIE coordinates were analyzed and calculated to be (0.297, 0.692).

Enzyme-trigger ratiometric fluorescent nanoplatform for diagnosis and imaging of oral diseases

Oral health is an essential part of overall health. Matrix metalloproteinase-2 (MMP-2) is a potential biomarker for diseases. The ability to accurately detect MMP-2 in vivo and in vitro is of great importance for the early diagnosis and prognosis, as well as the treatment evaluation, of oral diseases. In this study, cyanine 3 (Cy3) polypeptide containing the specific peptide substrate (PLGVR) of MMP-2 was modified onto SiO2-coated upconversion nanoparticles to fabricate a fluorescence resonance energy transfer (FRET)-based ratiometric fluorescent nanoplatform (UCNPs@SiO2@Cy3-pep). The green upconversion luminescence of UCNPs@SiO2 is quenched by Cy3, while its red upconversion luminescence is undisturbed. After Cy3 is cleaved at the PLGVR peptide by MMP-2, it is detached from the surface of UCNPs@SiO2, resulting in the recovery of green luminescence. Based on this principle, we applied UCNPs@SiO2@Cy3-pep to detect MMP-2 activity in different oral disease samples and models. We found that the level of MMP-2 in saliva of patients with oral cancer was 10 times higher than that of healthy individuals. In addition, the MMP-2 level in patients with periodontitis and severe dental caries also increased to varying degrees compared with that in healthy patients. Finally, in vitro and in vivo imaging experiments revealed that the nanoplatform was effective in monitoring MMP-2 level. Together, the developed nanoplatform can be an ideal tool for medical diagnosis of MMP-2-related diseases.

Pure Green Upconversion from a Multicolor Downshifting Perovskite Crystal

AbstractLanthanide‐doped halide perovskite has emerged as a promising phosphor for multimode luminescence. Here, a chloride‐based perovskite single crystal is reported, namely Cs2NaInCl6:Yb3+,Er3+, that is grown in a hydrothermal reactor. The as‐grown crystals feature two distinct luminescence behaviors under UV and 980 nm laser excitation, respectively. Under UV lamp excitation, the crystal shows a multicolor emission of sharp bands at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram. In stark contrast, the crystal under 980 nm excitation exhibits a pure green upconversion with a green‐to‐red ratio up to 211. The universal green dominance is further demonstrated in many chlorides, including Cs2AgInCl6, Cs2NaBiCl6, and Cs2AgBiCl6. The strong green upconversion is used for optical thermometry, which demonstrates an unprecedented sensitivity up to 9.3% K−1 at the low temperature end. The work introduces a kind of new hosts for single‐band upconversion luminescence, opening up many possibilities in areas such as low‐threshold laser and pure‐green color converter.

Luminescence enhanced temperature sensor based on the up-conversion emission in Er3+/Yb3+/Mo6+ tri-doped tellurite fiber

In this study, the green up-conversion (UC) fluorescence emission in Er3+/Yb3+/Mo6+ tri-doped tellurite glasses (TeO2–ZnO–Li2CO3–Bi2O3, TZLB) was explored for temperature sensing. The doping of Mo6+ ions allowed enhanced luminescence at moderate power pumping, avoiding the introduction of undesired laser-induced thermal effects while improving the spectral signal-to-noise ratio. The luminescence characteristics were investigated in detail at different doping molar ratio of Mo6+ ions, and the strongest was observed at 8 mol%. Drawing on tri-doped TZLB glass with the strongest UC emission intensity, a tri-doped TZLB fiber was fabricated and coupled with two multimode fibers (MMFs) via Ultraviolet (UV) adhesive, forming the temperature sensor. The sensor was further encapsulated by a silica tube sealed with Ultraviolet adhesive, overcoming the poor mechanical property of tellurite fiber. The temperature information could be demodulated based on the fluorescence intensity ratio technique. The temperature sensing performance of the tri-doped TZLB sensor was investigated as temperature varied from 258 to 420 K and its repeatability was experimentally verified. The Er3+/Yb3+/Mo6+ tri-doped TZLB has an application prospect in the field of lighting, and the so-based temperature sensor is expected to be applied to thermal detection in the fields of medical diagnostics, environmental monitoring, and optical thermometers, etc.

Ratiometric upconversion nanoprobes for turn-on fluorescent detection of hypochlorous acid

Ratiometric fluorescent nanoprobes have been developed for the detection of hypochlorous acid (HOCl) by simply mixing upconversion nanocrystals (UCNCs) with plasmocorinth B (PB) dye molecules, where UCNCs are adopted as the energy donor and dye molecules are introduced as the energy acceptor. Specifically, green upconversion luminescence (UCL) emission of UCNCs can be effectively quenched by PB, resulting from the spectral overlap between the absorption of PB and UCL emission of UCNCs in the green region. Furthermore, owing to the electrostatic repulsion between negatively charged UCNCs and PB dye molecules, the fluorescence quenching mechanism is based on the IFE process. Upon interaction with HOCl, PB dye molecules degrade, resulting in the recovery of green UCL emission through inhibition of the IFE process. The red UCL emission, however, remains unchanged. Therefore, the red UCL emission is employed as an internal reference signal for the ratiometric detection of HOCl. The detection limit of the nanoprobe for HOCl is quantified to be 1.12 µM, which is much lower than that of colorimetric detection. Moreover, the developed sensor has been successfully applied for quantitative monitoring of HOCl in tap water.

Emission colour tuning in KLnF4:Yb3+,Er3+/Ho3+ phosphor

KLnF4:Yb3+,Er3+/Ho3+ (Ln = Y, Yb, Gd) phosphors were prepared by solid-state reaction technique. For each of the Yb3+/Er3+ and Yb3+/Ho3+ co-doped phosphors independently, phase confirmation and morphological examination were accomplished using the X-ray diffraction technique and scanning electron microscope analysis. X-ray photoelectron spectroscopy analysis shows the charge state and existence of lanthanides and dopants. Upconversion luminescence emissions of green and red colour were detected for the synthesized phosphors. The changes in the upconverted emission intensities and colour output pertaining to the change of the lanthanide host matrix along with dopants were investigated for the prepared phosphors. In the upconversion luminescence, erbium-doped samples exhibit a predominance of red emission while holmium-doped samples display a prevalence of green emission. The rare-earth Er/Ho doped KYbF4 shows strong red emission compared to other hosts. KYF4:Yb,Er/Ho exhibits relatively significant green upconversion emissions, while Yb,Er-doped KGdF4 host displays a 10-fold increase in green/red emission ratio with an increase in the input power of 20–780 mW. Downshifting photoluminescence studies and decay curve analysis were carried out using UV light excitation for the developed phosphors. A higher lifetime of 2.2 ms was measured for the downshifting red emission in the Ho doped KYbF4 sample. This study suggests a potential for colour tunability in the upconversion and downshifting emissions through host modifications to the fluoride phosphor.