NIR Upconversion Emission Research Articles

Huge enhancement in upconversion luminescence near-infrared emission of KYb (MoO4)2: Er3+ phosphor by doping Y3+ ions

The KYb(MoO4)2: Er3+, Y3+ phosphors were synthesized by high temperature solid state reaction method. By further doping Y3+ ions, the near-infrared (NIR, 804 nm, 4I9/2 → 4I15/2) luminescence of KYb(MoO4)2: 0.1 % Er3+ phosphor is greatly enhanced. Based on the upconversion luminescence (UCL) spectra, the optimal doping concentration of Y3+ ions were 7.5 %. Its near-infrared UCL intensity is about 26.9 times that of undoped Y3+ ions. Through a series of characterization methods, we find that the enhancement of NIR upconversion emission is due to the generation of defect bands. It plays a crucial role in facilitating the transfer of energy from green light level (2H11/2, 4S3/2) to red light level (4F9/2) and near-infrared level. To explain the luminescence mechanism, the power dependence, UV-VI-NIR absorption spectra, excitation spectra at 804 nm and emission spectra at 380 nm were studied. In addition, the 804 nm single near-infrared UCL intensity of KYb (MoO4)2: Er3+, Y3+ shows a linear variation with temperature in the temperature range of 298 K–673 K. The maximum sensitivity is 0.13 % K−1. This study provides a new method and theoretical support for the application of near-infrared UCL in optical temperature measurement.

A signal processor made from DNA assembly and upconversion nanoparticle for pharmacokinetic study

The real-time drug-release monitoring is important for pharmacokinetic study toward clinical applications. The accuracy is usually severely affected by the fluctuation of complex biological microenvironment and dosage variation. Herein, a novel signal processor, upconversion nanoparticle (UCNP)-DNA nanocomplex (UCDC) was constructed via rational DNA design, enabling NIR-excited real-time in vivo drug-release monitoring, and realizing real-time pharmacokinetic monitoring. The signal processor was constructed by interfacial assembly of circular DNA on UCNP and the subsequent epitaxial assembly of ultralong DNA. Ultralong DNA chain was programed with multiple desired functional regions: double-stranded region for chemotherapy drugs integrating, DNA aptamer for tumor cells targeting and hairpin/i-motif switchable structure for tumor microenvironment responsive drug release. Based on filter effect of loaded drug molecules, efficient switch of real-time drug-release to optical signal was realized. For signal output, the ratiometer of red upconversion emission (UCLR) and NIR upconversion emission (UCLNIR) was monitored (UCLR/UCLNIR), with UCLNIR as an internal reference. In a breast cancer mouse model, the signal processor system achieved accurate and reliable localized drug-release monitoring, which effectively minimized the influence of the internal microenvironment and dosage variation.

Efficient NIR to NIR up-conversion in LiYF4:Yb3+,Tm3+ micro-octahedrons by modified hydrothermal method

The efficient NIR-to-NIR upconverter of LiYF4:Yb3+,Tm3+ (simplified as LYF:Yb,Tm) was synthesized by a modified hydrothermal method in this work. The synthesized LYF:Yb,Tm has well controlled morphology of monodisperse micrometer sized octahedrons. XRD pattern confirms its pure tetragonal LiYF4 structure. The LYF:Yb,Tm exhibits a dominating NIR UC emission at ~793 nm along with relative weak blue and red UC emissions under 976 nm LD excitation. The optimal concentrations of Yb3+ and Tm3+ ions for NIR up-conversion (UC) emission are 20 mol% and 0.6 mol%, respectively. The internal UC quantum yield (IUCQY) of this LYF:Yb,Tm in NIR band is tested to be 5.1% at 959 nm LD excitation power density (PD) of 120 W/cm2. The UC emission mechanism is discussed based on UC fluorescent behaviors of Yb3+ and Tm3+. The results of fluorescent labeling indicate its potential applications in fluorescent markers, solar cells and 3D flat panel displays.

Enhancing IR to NIR upconversion emission in Er3+-sensitized phosphors by adding Yb3+ as a highly efficient NIR-emitting center for photovoltaic applications

The IR to NIR upconversion emission is enhanced through codoping Yb3+ and the upconversion luminescence kinetics involved is investigated.

Construction of NaYF4:Yb,Er(Tm)@CDs composites for enhancing red and NIR upconversion emission

Upconversion luminescence can be tuned in NaYF4:Yb,Er(Tm)@CDs composites by efficient energy transfer.

Highly Efficient La2O3:Yb3+,Tm3+ Single-Band NIR-to-NIR Upconverting Microcrystals for Anti-Counterfeiting Applications.

Efficient single-band NIR-to-NIR upconversion (UC) emission is strongly desired for many applications such as fluorescent markers, plastic recycling, and biological imaging. Herein, we report highly efficient single-band NIR-to-NIR UC emission in La2O3:Yb3+,Tm3+ (LYT) microcrystals. Under 980 nm laser excitation, LYT exhibits a NIR UC emission at ∼795 nm (Tm3+: 3H4 → 3H6) and blue UC emission at ∼476 nm; the NIR UC emission is dominant, with the intensity ratio of the NIR to blue INIR/ Iblue > 100. Remarkably, a high absolute UC quantum yield (UCQY) of 3.4% is obtained for the single-band NIR UC emission of LYT at a relatively low excitation power density of 7.6 W/cm2. This value is much higher than the reported values of a single-band NIR UC for rare-earth-based UC materials in literature, such as the well-known benchmark UC materials of β-NaYF4:Yb3+,Er3+ (∼0.9%, with a excitation power density of 9 W/cm2) and Gd2O2S:Yb3+,Er3+ (∼1.9%, with a excitation power density of 20 W/cm2). The high absolute UCQY of single-band NIR UC emission combined with their facile preparation hints at their potential application in anti-counterfeiting, verified by the proof-of-concept demonstration of fluorescent labeling of a transparent IMT pattern.

Quantification of excitation-power dependency in Tm3 +/Yb3 + doped fluorotellurite upconverting glass phosphor for iris recognition

Excitation-power dependency of upconversion (UC) photons have been quantified in Tm3+/Yb3+ doped fluorotellurite (BALMT) glasses under the excitation of 975nm laser. The net powers of three-photon-excited blue and red and two-photon-excited NIR emissions are determined to be 242, 101 and 7994μW in 0.5wt% Tm2O3 and 2wt% Yb2O3 co-doping case under the excitation power of 870mW, respectively, and the net emission photon numbers are identified to be 58.2×1013, 33.0×1013 and 3253.2×1013cps. The quantum yields (QYs) for multi-photon-excited UC emissions of Tm3+ are identified as a positive dependency with pumping powers, and the relativity for three-photon fluorescence is extremely severe. When the excitation power density is set to 110.8W/mm2, the QY values for 476nm blue and 650nm red UC emissions are up to 1.49×10−4 and 0.84×10−4, and furthermore, the value for 809nm NIR UC emission is as high as 83.22×10−4. The 809nm luminescence is one of the good matching wavelengths for iris recognition in NIR ranges, the intensive NIR luminescence and the efficient blue fluorescence are promising in scanning and positioning for iris scanning. The macroscopic quantization for UC photon generation from Tm3+ in low-phonon fluorotellurite glasses provides a reliable reference for developing compact high-power-density light sources in iris recognition.

Frequency upconversion and downshifting emissions in solution combustion derived Yb3+, Pr3+ co-doped strontium aluminate nano-phosphor: A multi-modal phosphor

This paper reports the frequency upconversion and downshifting emissions from Yb3+, Pr3+ co-doped strontium aluminate nano-phosphor synthesized through solution combustion method. The structural measurements show nano-crystalline nature of the samples. The Fourier transform infrared measurements of the samples confirm the presence of different molecular species in the sample. The UV–vis–NIR spectrum of the sample shows absorption bands due to charge transfer band (CTB) and 4f–4f transition. The sample gives intense NIR upconversion emission centered at 854nm on excitation with 976nm laser. The emission intensity is optimum for 0.10mol% concentration of Pr3+ ion. The power dependent emission intensity measurement indicates the involvement of two photons for the upconverted emissions. The sample also emits intense blue upconversion and red downshifting emissions on excitation with 532nm laser. The emission intensity of the bands is enhanced significantly on annealing the samples at higher temperature. The large enhancement in the emission intensity is a combined effect of rare earth concentration, crystallinity and reduction in optical quenching centers. Thus, the multi-modal Yb3+, Pr3+ co-doped strontium aluminate nano-phosphor may be used for monochromatic source of NIR light, optical and display devices.

Insights into Er3+↔Yb3+ energy transfer dynamics upon infrared ~1550 nm excitation in a low phonon fluoro-tellurite glass system

Highly upconverting, monolithic transparent inorganic glass co-doped with Er3+/Yb3+ ions have been explored in view of their easy integration with Si-PV cell. A ~4 fold enhancement in the photo-current of mc-Si-PV cell has been observed using a Er3+/Yb3+ co-doped sample compared to Er3+ ions singly doped glass. The role of Yb3+ ions on the enhancement of photo-current has been discussed in light of the Er3+↔Yb3+ energy transfer mechanism involved from IR to NIR and VIS upconversion process upon IR ~1550nm excitation. The influence of excitation pump power and donor Er3+ ion concentration on the energy transfer upconversion (ETU) as well as excited state absorption (ESA) energy transfer mechanisms and its effect on the upconversion emission properties have been described in detail. The prominence of ETU or ESA process were elaborated considering the decay dynamics of NIR upconversion emission upon ~1550nm excitation.

Near infrared to blue upconverting Tm3+/Yb3+/Li+:Gd2(MoO4)3 phosphors for light emitting display devices

Tm3+-Yb3+/Tm3+-Yb3+_Li+ codoped/tridoped Gd2(MoO4)3 phosphors using chemical co-precipitation method have been synthesized and characterised by XRD, FTIR, diffuse reflectance spectra and FE-SEM analysis. The downconversion emission spectra recorded by using 390nm radiation shows blue colour emission band due to the 1G4→3H6 transition of Tm3+ ion. Frequency upconversion emission study show overall intense blue, red and NIR upconversion emission bands due to the 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ ion under 980nm laser diode excitation. The effect of incorporation of Li+ ions in the codoped phosphors produces small shifting in the XRD peaks towards the higher diffraction angle side and also intensity of the blue upconversion emission bands is enhanced around ∼510 times in the Tm3+-Yb3+_Li+:Gd2(MoO4)3 phosphors as compared to the Tm3+ doped phosphors. The confirmation of overall blue colour emission has been identified by colour co-ordinate analysis. The result shows that the developed tri-doped phosphors show improved blue colour emission and hence could be a proper material for near infrared to blue upconverter and blue colour emitting device fabrications.

NIR upconversion emission of Tm3+ doped glassceramics for solar cells applications

The Tm3+ 800nm upconversion emission corresponding to the 3H4→3H6 transition has been obtained upon infrared sub-Si bandgap excitation at 1210nm in Tm3+ doped transparent glasses and glass ceramics with composition SiO2–Al2O3–CdF2–PbF2–YF3. Possible energy transfer mechanisms have been carefully studied through different experimental measurements such as the excitation spectrum, decay rate of the emission and laser pump power versus integrated emission. The results suggest that energy transfer upconversion (ETU) mechanism is responsible for the emission. It is based on the following process: Tm3+(3F4)+Tm3+(3F4)→Tm3+(3H6)+Tm3+(3H4). The upconverted emission is about three times more intense in the glass ceramic samples than in the precursor glasses. This emission can be used to enhance the performances in crystalline silicon (c-Si) solar cells.

Enhanced near-infrared upconversion luminescence of GdF3:Yb3+, Tm3+ by Li+.

GdF3:0.23Yb3+, 0.005Tm3+, x%Li+ (x = 0-7) NIR to NIR upconversion nanocrystals (UCNPs) were synthesized by a hydrothermal method. Their XRD patterns show that they are all orthorhombic phase despite of different Li+ ion concentrations. The detailed analysis indicates that lithium ions substitute Gd3+ sites at x < 3. As the Li+ content increases, more Li+ ions enter host lattice interstitially. The doped Li+ ions affect the crystal field symmetry around Tm3+ ions, which results in the change of the irradiation transition probabilities between their corresponding transition levels. Compared with GdF3:0.23Yb3+, 0.005Tm3+, the NIR to NIR upconversion emission intensity of GdF3:0.23Yb3+, 0.005Tm3+, 0.03Li+ nanocrystals (excitation at 980 nm, emission at 808 nm) increases 2.2 times.

Enriched green upconversion emission in combustion synthesized Y2O3:Ho3+–Yb3+ phosphor

Ho3+ and Yb3+ co-doped Y2O3 phosphor has been prepared by the combustion route and its upconversion emission has been studied by using a 980 nm diode laser excitation. The powder XRD measurement has shown cubic phase of the sample. Prepared phosphors have shown good upconversion intensity and exhibited UV to NIR upconversion emission bands. The co-doping of Yb3+ in Y2O3:Ho3+ phosphor has found to enhance the Ho3+ emission intensity nearly ∼290 times. Interestingly, large part of the total upconversion intensity emitted by the sample was found to be concentrated around ∼545 nm which resulted pure green emission. For potential security applications, the upconversion based text reading concept has been demonstrated using this phosphor. The temperature sensing property of synthesized phosphor has also been studied by using the fluorescence intensity ratio of two nearby levels of green emission.

Effect of Yb3+ and Tm3+ concentrations on blue and NIR upconversion luminescence in Yb3+, Tm3+ co-doped CaMoO4

Polycrystalline Tm3+/Yb3+ co-doped CaMoO4 UC phosphors were successfully synthesized by a complex citrate-gel method and their upconversion (UC) luminescence was investigated. Under excitation at 980nm, Tm3+/Yb3+ co-doped CaMoO4 showed bright blue emission near 475nm generated by the 1G4→3H6 transition and strong NIR UC emission around 796nm generated by the 3H4→3H6 transition, with weak red emission near 650nm due to the 3F2→3H6 transition. The optimum doping concentrations of Tm3+ and Yb3+ for the highest UC luminescence were investigated, and the related UC mechanism of Tm3+/Yb3+ co-doped CaMoO4 depending on pump power was studied in detail.

Ultrasmall Monodisperse NaYF4:Yb3+/Tm3+ Nanocrystals with Enhanced Near-Infrared to Near-Infrared Upconversion Photoluminescence

Photoluminescent NaYF(4):Yb(3+)/Tm(3+) nanocrystals are ideally suited for in vitro and in vivo photoluminescence (PL) bioimaging due to their virtue of near-infrared to near-infrared (NIR-to-NIR) upconversion (UC); they display PL with a peak at approximately 800 nm if excited at approximately 980 nm. Here, we report the synthesis of monodisperse NaYF(4):Yb(3+)/Tm(3+) nanocrystals of ultrasmall size (7-10 nm) with high UC efficiency. The intensity of their NIR UC emission was demonstrated to increase by up to 43 times along with an increase in the relative content of Yb(3+) ions from 20 to 100%, with a corresponding decrease in the Y(3+) content from 80 to 0%. The achieved ultrasmall NaYbF(4):2% Tm(3+) nanocrystals manifest NIR PL emission, which is 3.6 times more intense than that from 25-30 nm sized NaYF(4):20% Yb(3+)/2% Tm(3+) nanocrystals, previously synthesized and used for in vitro and in vivo bioimaging. An optimization of both size and UC PL efficiency of NIR-to-NIR nanocrystals provides us with highly efficient optical imaging probes for bioapplications.