Near-infrared Upconversion Emission Research Articles

Optical transition and near-infrared upconversion luminescence properties of YNbO4: Er3+, Yb3+ phosphors

Optical transition and near-infrared upconversion luminescence properties of Er3+ single-doped and Er3+, Yb3+ co-doped YNbO4 phosphors are reported. Based on the framework of Judd-Ofelt theory and modified Judd-Ofelt calculation method, the optical transition properties of Er3+ and Yb3+ ions in YNbO4: Er3+, Yb3+ sample were studied, respectively. The calculated results showed that the absorption cross-section of Er3+ ion at ∼1550 nm is larger than that at ∼980 nm in YNbO4: Er3+ phosphor. And, the absorption cross-section of 2F7/2 → 2F5/2 transition of Yb3+ in YNbO4: 15.0 mol% Er3+, 15.0 mol% Yb3+ sample was calculated to be 138.70 × 10−20 cm2. According to the emission cross section of Er3+ (4I11/2 → 4I15/2) and the absorption cross section of Yb3+ (2F7/2 → 2F5/2), the energy transfer rates from Er3+ to Yb3+ were quantitatively analyzed via the Föster-Dexter model. Furthermore, 1550 nm was selected as the excitation wavelength, the near-infrared upconversion emission spectra of YNbO4: Er3+, Yb3+ samples were measured. It was found that the sample has strong emission at ∼980 nm and the emission intensity was still enhanced with the incorporation of Yb3+.

A NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods with infrared thermally enhanced upconversion luminescence for optical thermometers

A novel strategy for optical thermometers is reported based on the NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods which generate thermally enhanced near-infrared upconversion emission. The fluorescence intensity ratio (FIR) between the near-infrared emission of Tm3+ (3H4→3H6) and the green emission of Er3+ (4S3/2 → 4I15/2) as a function of temperature are studied. The relative sensitivity (Sr) of FIR (3H4→3H6/4S3/2 → 4I15/2) is compared with that of classical FIR (2H11/2 → 4I15/2/4S3/2 → 4I15/2). The results show that FIR (2H11/2 → 4I15/2/4S3/2 → 4I15/2) is suitable for low temperature, while FIR (3H4→3H6/4S3/2 → 4I15/2) is suitable for high temperature. Using FIR with higher Sr at different temperature intervals can keep the Sr of the thermometer at a higher value (0.67–1.07 %K−1) in the temperature range of 293–523 K. The results show that NaYF4:Gd3+/Yb3+/Er3+/Tm3+ nanorods can be used as high-quality candidates for thermometers with high sensitivity and wide temperature range.

Intense blue-emitting Yb/Tm-CaSiO3 wollastonite upconversion phosphors

Wollastonite is a naturally occurring mineral with a chemical formula of CaSiO3. Owing to outstanding mechanical, chemical, and thermal stabilities, wollastonites have become one of the most versatile industry minerals for applications in construction materials, cement, plastics, paints and coatings, friction, automobile brakes, ceramic and metallurgical applications to name a few. Despite technological importance, research on functional properties such as photon upconversion in wollastonites is still lacking. In this report, an initiative has been taken to demonstrate ultra-violet, blue, and near-infrared photon upconversion in CaSiO3 wollastonite via Yb and Tm doping. The wollastonite ceramics are synthesized via microwave hydrothermal technique followed up by heat-treatment in air. β-wollastonite (2M) phase in the synthesized samples has been confirmed by X-ray diffraction and a successful doping of Yb3+ and Tm3+ ions in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The most intense phonon band has been observed at 872 cm−1. Upon 980 nm excitation, ultraviolet, intense blue, and near-infrared upconversion emissions as well as downshifting infrared emissions are observed from Tm3+ ions as a result of sensitization by Yb3+. The temporal evolution of the emitting states is studied to understand the emission mechanism. An absolute upconversion quantum yield of the 20Yb/0.5Tm–CaSiO3 sample in the 400–850 nm range is 0.79%.

Intense green photoluminescence and upconversion-based intrinsic optical bistability in Ho3+/Yb3+ codoped CaSc2O4 and upconversion in Ho3+/Yb3+ codoped CaY2O4 phosphors

The present study details the downshifting, frequency upconversion and intrinsic optical bistability in CaSc2O4:Ho3+/Yb3+ and upconversion in CaY2O4:Ho3+/Yb3+ phosphors synthesized by a complex-based precursor solution method. The X-ray powder diffraction confirms the formation of highly crystalline phosphors with pure orthorhombic phase. Fourier transform infrared studies of synthesized phosphors show vibrational bands due to the presence of Ca–O, Sc–O and Y–O groups. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to presence of Ho3+ and Yb3+ ions. The values of optical band gap (Eg) are found to be 5.69 eV and 5.58 eV for the Ho3+/Yb3+ codoped CaSc2O4 and CaY2O4 phosphors, respectively. The Ho3+/Yb3+ codoped CaSc2O4 phosphors display intense green downshifting emission upon 454 nm excitations. The lifetime of green luminescence of CaSc2O4:Ho3+/Yb3+ phosphors with varied Yb3+ concentrations have also been measured. The decay curves show a non-exponential nature fitted to the Inokuti-Hirayama model and the energy transfer microscopic parameters have been also calculated. The Ho3+/Yb3+ co-doped CaSc2O4 and CaY2O4 phosphors display intense green alongwith weak blue, red, and near-infrared upconversion (UC) emissions upon 980 nm excitations. The spectral color purity (Sgr) of CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor is calculated to be 0.78. Importantly, the variation of pump power generates intrinsic optical bistability (IOB) in the CaSc2O4:Ho3+(1%)/Yb3+(5%) phosphor for the green emission, which is not observed in the CaY2O4:Ho3+(1%)/Yb3+(5%) phosphor. Therefore, the Ho3+/Yb3+ co-doped CaSc2O4 phosphor could potentially be used in UC-based devices, optical memory devices, optical gates, optical transistors and switching devices for optical communications.

The upconversion luminescence from visible to near-infrared in pyrosilicate C-Er2Si2O7

Rare earth pyrosilicate C-Er2Si2O7 ceramics were synthesized by the conventional solid-state reaction method. We observed strong photoluminescence (PL) peaks of Er3+ around 1546 nm with a lifetime of 135.4 μs at room temperature, which is longer than that of Er2Si2O7 films fabricated on Si substrate. Under 980 nm excitation, obvious blue, green, and red upconversion (UC) emissions of Er3+ are observed in this material, making C-Er2Si2O7 a potential material for color display. The luminescence mechanism that two and three photons participate in the energy level excitation was analyzed. Moreover, the near-infrared UC emission in the first biological window was also observed in C-Er2Si2O7, indicating that this material can be used in the in vivo field.

Green, red, and near-infrared up-conversion emission of NaY(MoO4)2:Er3+ submicrometric particles obtained by one-step synthesis, and its thermometric application

Lanthanide ion-based nonlinear optical processes for conversion of infrared radiation to visible radiation are well known. These processes have been used to produce efficient photonic devices for optical amplifiers in Telecom, bioimaging systems, solid-state lasers, temperature sensors, displays, and solar cells. Here, we obtained submicrometric spherical NaY(MoO4)2:Er3+ particles doped at 0.5, 1, 2, 5, 10, 15, and 20% (mol/mol, Er3+/Y3+ ions) by spray pyrolysis in one step, and we studied up-conversion emission as a function of the lanthanide ion content in the matrix. Characterization of the samples by XRD, FTIR, TEM, and luminescence spectroscopy confirmed that spherical particles with micro- and submicrometric diameters were produced. All the samples had tetragonal structure with space group I41/a. The up-conversion studies performed upon excitation at 980 and 1550 nm confirmed a two- and three-photon mechanism, respectively. The emission behavior depended on the Er3+ content, and the materials emitted photons in the green, red, and NIR region. In addition, color emission could be tuned by the Er3+ content. Next, we studied the up-conversion behavior of the materials as a function of temperature. Spectroscopy showed that the integrated intensity emission from thermally coupled levels (2H11/2 and 4S3/2) depended linearly on temperature. The particles obtained here could be useful sensitizers for solar cells, bioimaging systems, and luminescent thermometry devices.

Up-conversion luminescence properties and temperature sensing behavior of Nd3+/Yb3+/Tm3+ triply doped LaNbO4 phosphors under 808 nm and 980 nm excitations

LaNbO4: Nd3+/Yb3+/Tm3+ phosphors were synthesized via a solid-state reaction method. Under both 808 nm and 980 nm excitations, the effects of Tm3+ concentration and temperature on the up-conversion luminescence properties of Tm3+ were investigated. From the excitation power densities dependent up-conversion emission intensities, it was confirmed that the up-conversion luminescence process of Tm3+ was insensitive to sample temperature within the temperature range we studied. Under the excitations of 808 nm and 980 nm, both blue and red up-conversion emissions of Tm3+ kept two-photon and three-photon processes at various temperatures. And the near-infrared (NIR) up-conversion emission of Tm3+ was two-photon process when excited at 980 nm. Variation of the fluorescence intensity ratio (FIR) based upon the two thermally coupled energy levels 3F2,3 and 3H4 of Tm3+ with temperature was investigated and the temperature sensing behavior of Tm3+ was studied under 980 nm excitation. In the temperature range from room temperature to 663 K, the absolute temperature sensitivity of Tm3+ increases monotonously with the elevation of temperature, and the maximum value was obtained to be 3.702 × 10-4 K-1 at 663 K.

Structural and optical properties in Tm3+/Tm3+–Yb3+ doped NaLuF4 glass‐ceramics

AbstractTransparent NaLuF4 glass‐ceramics (GCs) doped with Tm3+ and Tm3+/Yb3+ have been prepared by melting‐quenching followed by thermal treatment at temperatures near the glass transition temperature. The crystallization process has been studied using X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM). NaLuF4 nanocrystals (NCs) ranging 9–30 nm in size are the only crystalline phase, the crystal size increasing with the dopant concentration. Energy dispersive X‐ray (EDX) measurements confirm the Tm3+ and Yb3+ incorporation in the NCs. Optical characterization included the analysis of up‐conversion (UC) as well as the Near‐infrared (NIR) luminescence. NIR emission spectra of Tm3+ and Yb3+ in co‐doped samples confirmed an efficient energy transfer between both ions. No UC emissions are observed in Tm3+ single‐doped glass and GCs. Yb3+ incorporation favors the Tm3+‐Tm3+ UC processes resulting in Tm3+ blue, yellowish‐red and NIR UC emissions after excitation at 975 nm. Blue UC emission is also observed in the codoped samples after Tm3+ excitation at 791 nm. These effects were more evident for the GCs compared to the base glasses, confirming the RE ions incorporation in the NCs. As a result, these GCs can be used to tune the UC emission from NIR to blue by selective excitation.

Enhanced one-band near infrared upconversion luminescence of Yb3+-Tm3+ co-doped BiOCl1-xBrx nanosheet by tuning band gap

Tm3+-Yb3+ codoped nanophosphor with highly efficient near-infrared (NIR) upconversion (UC), which is nearly pure NIR-to-NIR luminescence, exhibited great potential in revolutionary biological luminescence labels and super resolution fluorescence imaging on account of its depth of penetrability into tissue and high signal-to-noise ratio. Herein, we reported a different strategy to enhance the one-band NIR UC of Tm3+ ion by tuning the band gaps of polarized semiconducting nanosheets. Under excitation at 980 nm, increasing Br− concentration from 0 to 0.5, the one-band NIR UC emission generated by the 3H4→3H6 electric dipole transition (801 nm) in Tm3+-Yb3+ co-doped BiOCl1-xBrx nanosheets, was gradually enhanced accompanied by prolonged decay time, which was as a result of the high environmental sensitivity of the spontaneous host; however further increase of Br resulted to a contrasting effect. The results show that band gap tuning with Br− improved the separation efficiency of the photocarriers of the semiconducting nanosheets and led to asymmetrical local crystal field, which enabled the prolonged decay time of the excited energy levels of Tm3+ ions, and consequently, the UC enhancement. This work presents a new direction for the realization of efficient and pure NIR-to-NIR UC in fluorescent labelling probe and super resolution fluorescence imaging.

Nano-Crystallization of Ln-Fluoride Crystals in Glass-Ceramics via Inducing of Yb3+ for Efficient Near-Infrared Upconversion Luminescence of Tm3.

Transparent glass-ceramic composites embedded with Ln-fluoride nanocrystals are prepared in this work to enhance the upconversion luminescence of Tm3+. The crystalline phases, microstructures, and photoluminescence properties of samples are carefully investigated. KYb3F10 nanocrystals are proved to controllably precipitate in the glass-ceramics via the inducing of Yb3+ when the doping concentration varies from 0.5 to 1.5 mol%. Pure near-infrared upconversion emissions are observed and the emission intensities are enhanced in the glass-ceramics as compared to in the precursor glass due to the incorporation of Tm3+ into the KYb3F10 crystal structures via substitutions for Yb3+. Furthermore, KYb2F7 crystals are also nano-crystallized in the glass-ceramics when the Yb3+ concentration exceeds 2.0 mol%. The upconversion emission intensity of Tm3+ is further enhanced by seven times as Tm3+ enters the lattice sites of pure KYb2F7 nanocrystals. The designed glass ceramics provide efficient gain materials for optical applications in the biological transmission window. Moreover, the controllable nano-crystallization strategy induced by Yb3+ opens a new way for engineering a wide range of functional nanomaterials with effective incorporation of Ln3+ ions into fluoride crystal structures.

Near-infrared excitation and emitting thermometer based on Nd3+ doped ytterbium molybdate with thermally enhanced emissions

Lanthanides doped optical materials with temperature sensing property are of great interest for optical thermometry. However, most lanthanides doped luminescent materials for ratiometric thermometer are often accompanied by thermal quenching, which leads to a decrease in temperature sensing performance. Here, Nd3+ doped Yb2Mo3O12 phosphor with near-infrared upconversion emissions has been fabricated. A non-contact thermometer is constructed with the luminescence of Nd3+ ions and the change of the emission peak height ratio of 4F7/2-4I9/2 and 4F5/2-4I9/2 transitions. Interestingly, the intensity of the emission peaks in the prepared phosphor increases with increasing temperature. Avoiding thermal quenching, the thermally enhanced upconversion emission affords high sensing accuracy. The maximum relative and absolute sensitivity was 1.186% and 9.789 × 10−3 K−1, respectively. The results suggest that appropriate emission bands with thermal population are benefit for optical ratiometric thermometers.

Microwave hydrothermal synthesis and upconversion properties of BiVO4 nanoparticles

Nanomaterials are the subject of extensive investigations due to their applications in medicine, multimodal imaging, volumetric displays, and photonics. Here, lanthanide-doped bismuth vanadate (BiVO4) upconverting nanoparticles (UCNPs) have been reported. The nanoparticles have been synthesized by a microwave hydrothermal method. As-synthesized nanoparticles are highly crystalline in the tetragonal zircon phase with particles about 200 nm in size. Under 980 nm excitation, intense multicolor visible and near-infrared upconversion emissions are observed. Moreover, broadband infrared downshifting emissions are also observed. Time-resolved emission measurements have been carried out to investigate the involved upconversion and energy transfer mechanism. The BiVO4-based UCNPs may provide a new class of nanomaterials for multifunctional applications.

Single-band near-infrared upconversion emission and visible-light absorption in highly doped pseudo-perovskite oxides

Currently, concentration-induced near-infrared upconversion quenching at highly doped levels of lanthanide ions poses a significant constraint for their practical applications. In this work, the fabricated Tm3+/Yb3+ codoped Na0.5Bi2.5Nb2O9 (NBN) materials with a layered structure exhibited a single-band near-infrared to near-infrared upconversion emission (808 nm emission, 980 nm excitation) with no obvious concentration quenching even with a higher Yb3+ content of 90 mol%, while maintaining excellent thermal stability. Meanwhile, the Tm3+/Yb3+ co-doped NBN materials showed strong visible-light absorption at 400-800 nm under the irradiation with sunlight (AM1.5), and the absorbed light can be released via a thermal stimulus, showing a typical photochromic reaction. The near-infrared upconversion emission intensity was effectively tuned after and before sunlight irradiation. This research provides a new strategy for designing high-efficiency near-infrared upconversion and visible photoresponsive oxides for near-infrared modulation, solar energy conversion, and other multifunctional applications.

Silica-Coated Ga(III)-Doped ZnO: Yb3+, Tm3+ Upconversion Nanoparticles for High-Resolution in Vivo Bioimaging using Near-Infrared to Near-Infrared Upconversion Emission.

Photon avalanche has attracted much attention due to the unique nonlinear luminescence dynamics and high-efficiency upconversion luminescence properties. In this paper, we present a simple but effective method to prepare Yb/Tm/GZO@SiO2 (GZO = gallium-doped zinc oxide). Low-threshold photon-avalanche luminescence was obtained below the milliwatts (2.5 mW) in Yb/Tm/GZO@SiO2 core/shell nanoparticles. Compared with Yb/Tm/GZO nanoparitlces, near-infrared (NIR) upconversion luminescence intensity of Yb/Tm/GZO@SiO2 was enhanced ∼12 times. Furthermore, Yb/Tm/GZO@SiO2 acted as luminescence probe, which realized the red fluorescence imaging of myocardial tissue. With injection of 6 mg/kg Yb/Tm/GZO@SiO2, the red NIR fluorescence imaging of heart tissue became brighter. The experimental results of histological assessments of representative organs indicated that there was low toxicity of Yb/Tm/GZO@SiO2 in vivo. This study proved that Yb/Tm/GZO@SiO2 posed a promising potential for bioimaging applications.

BiVO4 as highly efficient host for near-infrared to visible upconversion

BiVO4 is a well-known visible-light-active semiconductor photocatalyst. Here, we report BiVO4 as a highly efficient host material for near-infrared (NIR) to visible frequency upconversion. Various lanthanide ions (Yb, Er, and Tm) doped BiVO4 upconversion phosphors were successfully synthesized through a facile microwave hydrothermal method. As-synthesized samples exhibit intense green, red, and NIR upconversion emissions under 980 nm excitation at power density as low as 0.02 W cm−2. The quantum efficiency for Yb, Er, and Tm triply doped BiVO4 under 2.0 W cm−2 was as high as 2.19% in the 500–850 nm range. Moderately low phonon energy (824 cm−1) of BiVO4 was found to be responsible for the existence of long-lived metastable energy levels leading to efficient upconversion emissions. Potential application of the material for producing latent images and security printing has been demonstrated. The high quantum efficiency of BiVO4 offers an opportunity to develop alternative upconversion materials based on the BiVO4 host for various optical applications.

Small lanthanide-doped Sr2YbF7 nanocrystals: Upconversion fluorescence and upconversion-driven photodegradation

A series of lanthanide-doped Sr2YbF7 nanocrystals were prepared conveniently via a solvothermal method using oleic acid as the stabilizing agent, which were about 15 nm of the average crystalline size at 200 °C and 24 h. Through screening the doped lanthanide ions and their concentrations, we found that the nanocrystals realized intense ultraviolet, visible and near-infrared upconversion emissions under 980 nm excitation. Based on the photo-physical property of the nanocrystals, we built the hybrid Sr2YbF7: Tm3+@TiO2 to successfully realize upconversion-driven photo-degradation of Rhodamine B, in which semiconducting TiO2 took advantage of the light emitted by Sr2YbF7: Tm3+ to produce the electron-hole pairs.

Near-infrared up-conversion emission from erbium ions doped amorphous tellurite media: Judd-Ofelt evaluation

Efficient up-converted lasing materials are required for high performing, durable and low cost photonic devices. Rare earth ions doped glass systems with modified optical properties may meet this need. In this view, erbium (Er3+) ions doped zinc-magnesium-tellurite glass system of composition (75-x)TeO2–15ZnO–10MgO–xEr2O3 (0.5 ≤ x ≤ 2.0 mol%) was prepared via melt-quenching method. Optical behavior of such glasses was determined as a function of changing Er2O3 content to examine the feasibility of achieving up-converted lasing media. Judd-Ofelt (J-O) intensity (Ω2, Ω4, Ω6) and radiative parameters were evaluated. Glass hardness was increased linearly with increasing Er3+ ions concentration. The emission spectra revealed three peaks around 470 nm, 500 nm and 550 nm. Effect of Er2O3 content on the 4I13/2 → 4I15/2 transition was quantified in terms of fluorescence intensity and lifetime. The width of the near-infrared fluorescence band (1.53 μm) was broadened from 58.77 to 60.01 nm with the increase of Er2O3 content from 0.5 to 2.0 mol%. The proposed glass compositions were demonstrated to be potential for solid-state lasers, near infrared sensors, and other optical devices.

Microwave hydrothermal synthesis and upconversion luminescence properties of $$\hbox {Yb}^{3+}$$ Yb 3 + / $$\hbox {Tm}^{3+}$$ Tm 3 + co-doped $$\hbox {NaY}(\hbox {MoO}_{4})_{2}$$ NaY ( MoO 4 ) 2 phosphor

Tetragonal \(\text {NaY}(\text {MoO}_{4})_{2}\) (NYM) phosphors co-doped with \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM displayed bright blue emission near 472 and 476 nm (\(^{1}\hbox {G}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition), strong near-infrared upconversion (UC) emission around 795 nm (\(^{3}\hbox {H}_{4}\rightarrow {}^{3}\hbox {H}_{6}\) transition). The optimum doping concentrations of \(\hbox {Yb}^{3+}\) and \(\hbox {Tm}^{3+}\) for the most intense UC luminescence were obtained, and the related UC mechanism of \(\hbox {Yb}^{3+}\)/\(\hbox {Tm}^{3+}\) co-doped NYM depending on pump power was studied in detail.

Blue, green, red and near-infrared emissions via upconversion in α-sialon

Near-infrared to visible and near-infrared upconversion emission has been reported in Yb3+/Ln3+ (Ln3+=Er3+/Tm3+/Ho3+)-α-sialon ceramic prepared by hot press sintering technique. Under 980nm excitation, blue, green, red and near-infrared emissions are observed simultaneously as a result of the efficient energy transfer from Yb3+ to Er3+, Tm3+, and Ho3+ ions leading to a near-white light emission with CIE color coordinate of (0.38, 0.45). The two- and three-photon absorption processes are responsible for the observed upconversion emissions. The ceramic has moderately low phonon energy of 835cm−1. These novel properties make the material a promising candidate for upconversion applications.

Visible and near-infrared upconversion in α-sialon ceramics

Intense near-infrared to visible and near-infrared upconversion emissions are realized in Er3+/Ho3+/Tm3+ doped α-sialon ceramics.