Near-infrared Downconversion Luminescence Research Articles

Simultaneous Observation of Visible Upconversion and Near-Infrared Downconversion in SrF2:Nd3+/Yb3+/Er3+ Nanocrystals and Their Application for Detecting Metal Ions under Dual-Wavelength Excitation.

In this work, a sequence of Nd3+, Yb3+, and Er3+ tridoped SrF2 nanocrystals (NCs) is synthesized by a hydrothermal method. Both the efficient near-infrared downconversion luminescence (DCL) and visible upconversion luminescence (UCL) of the Er3+ and Nd3+ ions are simultaneously observed and systematically demonstrated under dual-wavelength excitation (808 and 980 nm continuous-wave lasers). Subsequently, the SrF2:Nd3+/Yb3+/Er3+ (15/4/0.2 mol %) NCs with the strongest luminescence were utilized for detecting the metal ion concentrations under 808 nm excitation. The results reveal that both the UCL and DCL gradually decrease as the metal ion concentrations increase, and high sensitivity is obtained for Cu2+ ions with a detection limit of 0.22 nM (∼650 nm) and 0.63 nM (∼976 nm). In addition, these SrF2:Nd3+/Yb3+/Er3+ NCs are further demonstrated to achieve a solid-state display under 980 nm excitation, exhibiting obvious “red” and “green” patterns by varying the doping rare earth ion concentrations.

Enhanced near-infrared downconversion luminescence in ZnxNb(1-x)O composite host co-doped Bi3+ /Yb3+ phosphor for Si solar cell applications

The spectral modification is noticed through near Infrared (IR) downconversion (DC) in Yb3+, Bi3+ co-doped ZnxNb(1-x)O composite host. A high-intensity blue emission centered at 450 nm is observed upon UV excitation at 270 nm for the host ZnxNb(1-x)O at x = 0.5 (ZN). Doping with the optimized concentration at 4 mol% of Yb3+ with ZN (YZN) initiates an energy transfer from the niobate group to two neighboring Yb3+ ions in a co-operative energy transfer (CET) process. The resulting Yb3+ emission spectrum is around 1000 nm, which matches well with the spectral response of Si solar cells. Introducing 1 mol% of trivalent Bi3+ ions as an additional sensitizer to YZN (BZN), the excitation wavelength is further extended from UV at 270 nm to visible at 450 nm region. As an effect of this, UV excitations at 270 nm, 330 nm, and visible excitation at 450 nm in BZN enhance the luminescence in the near IR region. The DC process observed in BZN is due to the CET process from both the niobate group and Bi3+ ions to Yb3+ ions. Solar panel coated with BZN shows an increase in conversion efficiency which in turn indicates that the synthesized phosphor is a promising material for increasing Si solar cell efficiency.

Plasmon enhanced near-infrared downconversion luminescence of β-NaYF4:Pr3+ nanoparticles by high-ordered Ag nanopillar arrays with tunable nanogaps

Large-area high-ordered Ag nanopillar arrays with tunable nanogaps are fabricated by an electroless deposition method. Then, β-NaYF4:Pr3+ nanoparticles (NPs) are spin coated on the Ag nanopillar arrays. Plasmon enhanced near-infrared (NIR) downconversion (DC) luminescence involving the 876 nm (1D2→3F2) and 1017 nm (1D2→3F4,3), as well as the two-step sequential transitions at 915 nm (3P0→1G4) and 990 nm (1G4→3H4), are achieved by Ag nanopillar arrays under the excitation of 444 nm (3H4→3P2) of Pr3+ ions. The influence of different nanogaps between Ag nanopillar arrays on NIR DC luminescence is investigated, and the results show that the optimal nanogap size is 25 nm with a maximum enhancement factor about 3.98. Furthermore, 3D finite-difference time-domain (FDTD) simulation is performed to analyze the enhancement mechanism of NIR DC luminescence. Our study may have potential application in the field of silicon-based solar cells.

Broadband near-infrared downconversion luminescence in Yb3+-doped BaZn2(BO3)2

BaZn2(BO3)2 self-activated phosphors were prepared by the conventional high temperature solid-state method. The PL spectra of BaZn2(BO3)2 powders prepared under reductive and air atmosphere consist of a weak ultraviolet emission band (∼410 nm) and a broad emission band which were centered at ∼ 500 and 545 nm, respectively. According to the spectral analysis and EPR results, the green and yellow emissions may arise from the transitions of photo-generated electron close to the conduction band to the deeply trapped hole in single ionized oxygen vacancy (V+ o) centers and single negatively charged interstitial oxygen ion (O- i), respectively. An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Yb3+ doped BaZn2(BO3)2 phosphor. Upon excitation with an ultraviolet photon at 375 nm, the emissions of two NIR photons at 983 nm from Yb3+ ions were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency, and the quantum efficiency on the Yb3+ doping content were investigated in detail. The results indicated that the maximum energy transfer and the corresponding downconversion quantum efficiency could reach between 68.5% and 168.5%.

Tunable ultraviolet/visible to near-infrared down-conversion luminescence in the Er3+, Yb3+ co-doped (Y0.88La0.09Zr0.03)2O3 transparent ceramics

Herein, we report an efficient ultraviolet/visible to near-infrared (NIR) down-conversion luminescence phenomenon in transparent Er3+, Yb3+ co-doped (Y0.88La0.09Zr0.03)2O3 ceramics. Almost fully densified (Y0.88La0.09Zr0.03)2O3 transparent ceramic has been prepared by vacuum sintering at 1800 °C with different contents of Er3+ and Yb3+ elements. The intensity ratio of Yb3+: 2F5/2 → 2F7/2 emission (∼1000 nm) to the Er3+: 4I13/2 → 4I15/2 emission (∼1550 nm) has been tuned by adjusting the excitation wavelength. Phonon-assist quantum cutting from the 4G11/2 level of Er3+ with two energy transfer (ET) processes to Yb3+ has been determined, which enhances the Yb3+ emission around the wavelength of 1000 nm. It is found that when one photon around 379 nm is absorbed, two photons around 1000 nm will be emitted, and hence the quantum efficiency is estimated to be ∼182% in this transparent ceramics. The mechanism of the visible to near-infrared (NIR) down-conversion luminescence in the Er3+, Yb3+ co-doped (Y0.88La0.09Zr0.03)2O3 ceramics has been discussed.

Single red upconversion and near-infrared downconversion luminescence properties of cubic ZrO2:Y3+-Yb3+-Er3+ nanophosphors via microwave hydrothermal synthesis

The Yb3+-Er3+-Y3+ tri-doped cubic ZrO2 (brief as YSZ:Yb, Er) nanophosphors with different Yb3+ (Er3+) doping concentrations have been prepared by microwave hydrothermal method followed by further calcining treatment. X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra were used to characterize the properties of YSZ:Yb, Er nanophosphors. Under the 980 nm excitation, the sample gives a set of upconversion light: very strong red emissions near 655 and 679 nm (4F9/2 → 4I15/2), very weak green (525 nm 2H11/2 → 4I15/2, 544 nm and 557 nm 4S3/2 → 4I15/2). Moreover, the sample gives near-infrared downconversion emission (1530 nm 4I13/2 → 4I15/2). Concentration dependent studies revealed that the optimal composition was realized for the 15 at% Yb3+ and 1 at% Er3+-doping concentration with a strong pure red emission. All the results indicate that YSZ:Yb, Er nanophosphors could be a promising biological labeling materials.

Molecular-like Ag clusters sensitized near-infrared down-conversion luminescence in oxyfluoride glasses for broadband spectral modification

Molecular-like Ag clusters sized at 1–4 nm have been stabilized in Pb/Cd-free oxyfluoride glasses, showing broadband excitation/emission characteristics and unique wavelength-dependent luminescent performance with a maximal quantum yield of 26.9%. It was experimentally demonstrated that an energy transfer route of Ag clusters → Tb3+ → Yb3+ occurs in Ag+/Tb3+/Yb3+ tri-doped sample, wherein Ag clusters act as sensitizers for near-infrared down-conversion spectral modification. Hopefully, the proposed strategy that noble metal clusters being applied for harvesting solar radiation may potentially solve the sticky problems of the narrow excitation bandwidth and the low excitation efficiency in rare earth ions doped down-conversion materials.

Broadband near-infrared downconversion luminescence in Eu2+–Yb3+ codoped Ca9Y(PO4)7

An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Eu2+–Yb3+ codoped Ca9Y(PO4)7 phosphor. Upon excitation of Eu2+ ions to the 4f65d1 level with an ultraviolet photon at 322nm, emissions of two NIR photons at 983nm of Yb3+were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency (ETE), and the quantum efficiency (QE) on the Yb3+ doping content were investigated in detail. The results indicated that the maximum ETE and the corresponding downconversion QE can reach between 80% and 179%, respectively.

Bimodal Imaging Using Neodymium Doped Gadolinium Fluoride Nanocrystals with Near-Infrared to Near-Infrared Downconversion Luminescence and Magnetic Resonance Properties.

Here we report the synthesis, characterization and application of a multifunctional surface functionalized GdF3:Nd3+ nanophosphor that exhibits efficient near infrared (NIR) fluorescence as well as magnetic properties, which can be utilized for bimodal imaging in medical applications. The nanoparticles are small with an average size of 5 nm and form stable colloids that last for several weeks without settling, enabling the use for several biomedical and photonic applications. Their excellent NIR properties, such as nearly 11 % quantum yield of the 1064 nm emission, make them ideal contrast agents and biomarkers for in vitro and in vivo NIR optical bioimaging. The nanophosphors which were coated with poly(maleic anhydride- alt-1-octadicene) (PMAO) were implemented in cellular imaging and show no significant cellular toxicity for concentrations up to 200 μg ml-1. Furthermore, the incorporation of Gd into the nanocrystalline structure supplies exceptional magnetic properties, making them ideal for use as magnetic resonance imaging (MRI) contrast agents. The utility of these NIR emitting nanoparticles in infrared bioimaging and as contrast agent in magnetic resonance imaging was demonstrated by confocal imaging, magnetic resonance and tissue experiments.

Visible to near-infrared down-conversion luminescence in Tb3 + and Yb3 + co-doped lithium–lanthanum–aluminosilicate oxyfluoride glass and glass-ceramics

Tb3+ and Yb3+ co-doped oxyfluoride glasses were fabricated in a lithium–lanthanum–aluminosilicate matrix (LLAS) by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion luminescence was studied for glass and glass-ceramic samples with different Yb3+ concentrations. It has been found that the luminescence intensity at 940–1020nm from Yb3+ ions increases while the emission lifetime of Tb3+ ions decreases in the glass-ceramic compared to that in the as-prepared glass, which indicates that the energy transfer efficiency increases in the glass-ceramics compared to that in the as-prepared glass. The down-conversion luminescence also increased for increasing Yb3+ concentration from 1mol% to 2mol%, but decreased for the sample with a high Yb3+ co-doping concentration of 8mol%, which is attributed to the concentration quenching.

Lanthanide dopant-induced formation of uniform sub-10 nm active-core/active-shell nanocrystals with near-infrared to near-infrared dual-modal luminescence

We present a novel strategy involving the lanthanide dopant-induced formation of ultrasmall (sub-10 nm) uniform Ln3+:BaF2/Ln3+:SrF2 active-core/active-shell architectures. The lanthanide ions doped in the shell are demonstrated to play a key role to retard the growth of the core/shell nanocrystals. Particularly, adopting ∼3 nm Tm3+,Yb3+:BaF2 nanocrystals as cores prepared by a solvothermal reaction, growth of Gd3+,Nd3+:SrF2 shells is successfully induced on the surfaces of these cores through a thermal decomposition process, forming ∼7 nm highly uniform and monodisperse Tm3+,Yb3+:BaF2/Gd3+,Nd3+:SrF2 active-core/active-shell nanocubes. In this architecture, the Gd3+,Nd3+:SrF2 shell not only benefits the enhancement of the near-infrared to near-infrared upconversion luminescence of the Tm3+,Yb3+:BaF2 core, but also acts as the host to realize the near-infrared to near-infrared downconversion luminescence of Nd3+ dopants and the paramagnetism of Gd3+ ones. Importantly, the doping of Tm3+/Yb3+ and Nd3+ into the core and shell respectively effectively suppresses the adverse energy transfer from Tm3+ to Nd3+ as well as from Nd3+ to Yb3+, resulting in lessening of the quenching for both Tm3+ upconversion and Nd3+,Yb3+ downconversion emissions. These hydrophobic core/shell nanocrystals are further converted into hydrophilic ones using thioglycolic acid as the surface ligand. The sub-10 nm water-soluble active-core/active-shell architectures with near-infrared to near-infrared dual-modal luminescence and proper paramagnetism may find potential applications in biomedical imaging and detection.

Broadband UV excitable near-infrared downconversion luminescence in Eu 2+/Yb 3+:CaF 2 nanocrystals embedded glass ceramics

Cooperative downconversion was realized in glass ceramics containing Eu 2+/Yb 3+:CaF 2 nanocrystals with Eu 2+ greatly absorbing ultraviolet photons. Upon excitation of Eu 2+ ions to the 5 d level with an ultraviolet photon at 320 nm, emission of two near infrared photons at 976 nm of Yb 3+ were achieved. The dependence of the visible and near-infrared emissions, decay lifetime, and quantum efficiency on the Yb 3+ doping content has been investigated. The maximum energy transfer efficiency and the corresponding downconversion quantum efficiency were estimated to be 51% and 151%, respectively.