Spectroscopic properties and energy transfer of Nd3+/Ho3+-doped Ga2O3-GeO2 glass by codoping Yb3+ ion

This study presented the luminescence properties of Nd³⁺/Yb³⁺/Ho³⁺ dopant ions inside a host based on Ga₂O₃-GeO₂-Li₂O（GGL） glass. The measured differential scanning calorimetry result showed that GGL glass exhibited excellent stability against devitrification with ?T=135 oC. Obvious 543 and 657 nm emissions were observed in Nd³⁺/Ho³⁺-codoped sample. The incorporation of Yb³⁺ into Nd³⁺/Ho³⁺-codoped glass system had resulted in enhanced upconversion emission intensity under the excitation of 808 nm and/or 980 nm laser diode（LD）. The possible mechanisms and related discussions on this phenomenon were presented. It was noted that the presence of Yb³⁺ yielded an enhancement about 7 and 11 times in the 543 and 657 nm emission intensities respectively under 808 nm excitation due to the energy transfer from Nd³⁺ to Ho³⁺ via Yb³⁺ ion. Here Yb³⁺ played a major role as a bridging ion. While enhanced 543 and 657 nm emission intensities under the excitation of 980 nm LD originated from the sensitization effect of Yb³⁺. Our results showed that Nd³⁺/Ho³⁺/Yb³⁺ triply doped GGL glass might be a promising candidate for the development of visible-laser materials.     

Dual excitable upconversion nanoparticle@polydopamine nanocomposite with intense red emission and efficient photothermal generation

Integration of strong upconversion emission with deep tissue penetration and stable photothermal generation is of great significance for imaging-guided photothermal therapy under infrared excitation.Herein,the NaYF4:Yb³⁺,Ho³⁺,Ce³⁺ @NaGdF₄:Yb³⁺,Nd³⁺@NaGdF₄ core-shell-shell upconversion nanoparticles(UCNPs) with increasing Ce³⁺ doping concentration were firstly synthesized,in which the size manipulation,enhance...     

Decorating rare-earth fluoride upconversion nanoparticles on AuNRs@Ag core-shell structure for NIR light-mediated photothermal therapy and bioimaging

Photothermal therapy(PTT)has presented its inherent application value in cancer treatment.Nevertheless,single-functional photothermal materials cannot meet the precise diagnosis and treatment of cance r.Therefo re,it is important to design a nanocomposite that has both high therapeutic efficiency and multimodal imaging capabilities.In our work,a new nanostructure of gold nanorods(AuNRs)with silver shells decorated by BaGdF5:Yb³⁺,Er³⁺nanoparticle was synthesized by a simple way.The biostability of AuNRs is increased by coating with silver shells,and the AuNR@Ag nanoparticles can be used as excellent surface enhanced Raman scattering(SERS)probe.Moreover,the modification of BaGdF5:Yb³⁺,Er³⁺nanoparticles provides the possibility of real-time optical imaging of the tumor area.Under the irradiation of NIR laser,the AuNR@Ag/BaGdF5:Yb³⁺,Er³⁺nanocomposites(NCs)have strong upconversion emission and excellent photothermal conversion efficiency.Meanwhile,the NCs show low cytotoxicity and good biocompatibility in MTT cytotoxicity test.Moreover,the NCs are also exceptional contrast agents for CT imaging.For in vitro photothermal therapy test,NCs show excellent killing efficiency on tumor cells.Therefore,the multifaceted research of AuNR@Ag/BaGdF5:Yb³⁺,Er³⁺multifunctional nanomaterials provides a break for high-efficiency tumor photothermal therapy and multimodal imaging.     

Optical thermometry based on near-infrared luminescence from phosphors mixture

Luminescence ratiometric thermometry based on rare earth(RE)ions has attracted great interest for the potential applications in many fields.But the improvement of the measurement sensitivity and accuracy is significantly restricted due to the small energy gap between thermally coupled levels(TCL).Here,a strategy striving for good thermometric properties of luminescent materials was designed by using the phosphors mixture composed of NaY(WO₄)₂:Nd³⁺-Yb³⁺and NaY(WO₄)₂:Er³⁺,which were prepared by secondary sintering method.Under the excitation of 980 nm lase r,the near-infrared(NIR)emissions(710-920 nm)from Nd³⁺ions are effectively strengthened when the temperature increases from 304 to773 K,whereas Er³⁺NIR luminescence centered at around 1536 nm is thermally quenched.The remarkably different response of NIR emissions to the thermal variation allows us to map temperature through the ratiometric method.By optimizing the dopant concentration of rare earth(RE)ions,a maximum sensitivity of 5.14%/K together with a measurement uncertainty of about 0.1 K is acquired at304 K,which is superior to the previously reported RE luminescence-based temperature sensors,indicating that the approach developed here can pave the way for achieving optical thermometry with desired properties.     

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 dop...     

Er~(3+)-Yb~(3+)-Na~+:ZnWO_4 phosphors for enhanced visible upconversion and temperature sensing applications

The crystal structure and surface morphology of the Er³⁺/Yb³⁺/Na+:ZnWO₄ phosphors synthesized by solid state reaction method were analyzed by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) analysis.The frequency upconversion(UC) emission study in the developed phosphors was investigated by using 980 nm laser diode excitation.The effect of codoping in the Er³⁺:ZnWO₄ phosphors on the UC emission intensity was studied.The UC emission bands that are exhibited in the blue(490 nm),green(530,552 nm),red(668 nm) and NIR(800 nm) region correspond to the ⁴F_7/2→⁴I_15/2.²H_11/2,⁴S_3/2→⁴I_15/2,⁴F_9/2→⁴I_15/2 and ⁴I9/2→⁴I_15/2 transitions,respectively.The temperature sensing performance of the Er³⁺-Yb³⁺-Na+:ZnWO₄ phosphors was investigated based on the 2 H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 thermally coupled transitions of the Er³⁺ions.The photometric study was also carried out for the developed phosphors.     

White up-conversion luminescence and highly-sensitive optical temperature sensing in Na3La(VO4)2:Yb,Er,Tm,Ho phosphors

In this work,tunable white up-conversion luminescence was achieved in the Yb³⁺,Er³⁺,Tm³⁺,Ho³⁺ codoped Na₃La(VO₄)₂ phosphors under 980 nm excitation.The emissions of three primary colors are mainly attributed to the ²H_11/2/⁴S_3/2→⁴I_15/2 transitions of Er³⁺,¹G₄→³H₆ transition of Tm³⁺,and_5...     

Suppression of inner energy dissipation in Yb-doped NaErF4 upconversion nanocrystals through an energy cycling strategy

Suppression of the inner energy dissipation,related to the lattice phonons and inner defects,in lanthanide doped upco nversion luminescent materials remains a formidable challenge.Herein,we reveal an energy cycling strategy capable of suppressing the inner energy dissipation in lanthanide doped upconversion nanocrystals.Yb³⁺ ions were introduced in Er³⁺ heavily doped nanocrystals as an energy reservoir to compete with the inner energy dissipation.The detailed energy cycling...     

Gd3+ ion induced UV upconversion emission and temperature sensing in Tm3+/Yb3+:Y2O3 phosphor

Cubic phase Tm³⁺/Yb³⁺:Y₂O₃ and Tm³⁺/Yb³⁺/Gd³⁺:Y₂O₃ phosphors were prepared by low temperature combustion technique for upconversion emission in UV-visible range.The 980 nm excitation has generated UV emission at 314 nm in tridoped phosphor due to the energy transfer from Tm³⁺ to Gd³⁺ion.Characteristic emission bands from Tm³⁺ are also observed in both the phosphors....     

Down- and up-conversion processes in Nd3+/Yb3+ co-doped sodium calcium silicate glasses with concomitant Yb2+ assessment

Novel Nd³⁺/Yb³⁺ co-doped sodium calcium silicate glasses were prepared by melting quenching method:Spectroscopic study was carried out as a function of doping content by fixing sensitizer(Nd³⁺) concentration to 0.2 mol% and adjusting activator(Yb³⁺) from 0 to 1.0 mol%.The energy transfer(ET)mechanisms between Nd³⁺and Yb³⁺ are discussed based on their energy levels and excitation powerdependence emission intensity.Results show that...     

Synthesis of NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 nanorods and their size dependent uptake efficiency under flow condition

Lanthanide doped fluorescent nanoparticles have gained considerable attention in biomedical applications. However, the low uptake efficiency of nanoparticles by cells has limited their applications. In this work, we demonstrate how the uptake efficiency is affected by the size of nanoparticles under flow conditions. Using the same size NaYF₄:20% Yb³⁺,2% Er³⁺,2% Ce³⁺ (the contents of rare earths elements are in molar fraction) nanoparticles as core, NaYF₄:20% Yb³⁺,2% Er³⁺,2% Ce³⁺@NaYF₄ core–shell structured nanorods (NRs) with different sizes of 60–224 nm were synthesized by thermal decomposition and hot injection method. Under excitation at 980 nm, a strong upconversion green emission (541 nm, ²H_11/2 → ⁴I_15/2 of Er³⁺) is observed for all samples. The emission intensity for each size nanorod was calibrated and is found to depend on the width of NRs. Under flow conditions, the nanorods with 96 nm show a maximum uptake efficiency by endothelial cells. This work demonstrates the importance of optimizing the size for improving the uptake efficiency of lanthanide-doped nanoparticles.     

Energy transfer and cross-relaxation induced multicolor upconversion emissions in Er~(3+)/Tm~(3+)/Yb~(3+) doped double perovskite La_2ZnTiO_6 phosphors

Investigation on the bright and stable upconversion(UC) phosphors with multicolor emissions is fundamental and significant for the frontier applications of display and tempe rature probe.He re,dive rse emitting colors with blue,cyan and yellowish green,which are caused by the energy transfer and crossrelaxation processes,are obtained by altering Er~(3+),Tm~(3+)and Yb~(3+) concentrations in Er~(3+)singly,Er~(3+)-Tm~(3+)-Yb~(3+)co-and tri-doped double perovskite La_2 ZnTiO_6(LZT) phosphors synthesized by a simple solid-state reaction.In addition,excellent infrared emission at 801 nm located at "first biological windo w" is collected in Tm~(3+)-Yb~(3+)co-doped phosphors.Meanwhile,the temperature sensing properties based on the thermally coupled levels(~2 H_(11/2)/~4S_(3/2)) of Er~(3+) ions were analyzed from 298 to 573 K of LZT:0.15 Er~(3+)/0.10 Yb~(3+)phosphor,demonstrating that the maximal sensitivity value is about56×10-4 K~(1-) at 448 K.All these results imply that this kind of UC material has potential applications in display,bioimaging and optical device.     

Multicolor luminescence of hexagonal NaYF4:Yb3+/Ho3+/Ce3+ microcrystals with tunable morphology under 940 nm excitation for temperature-responsive anti-counterfeiting

In this study, the hexagonal NaYF₄:Yb³⁺/Ho³⁺/Ce³⁺ microcrystals were synthesized controllably, and upconversion luminescence excited at 940 nm and its application in temperature-responsive anti-counterfeiting are reported. It is clarified that the Ln³⁺ (Ln = Y + Yb + Ho + Ce) density ratio of bottom plane to side plane in the unit cell can be regulated by Ce³⁺ doping. It is also proved that the energy transfer of Yb³⁺ to Ho³⁺ is responsible for the activation of Ho³⁺ under 940 nm excitation, while the cross relaxation between Ho³⁺ and Ce³⁺ participates in the redistribution of electron population of ⁵S₂/⁵F₄ and ⁵F₅ levels. Both theory and experiment confirm that the intensity ratio of red to green emission (I_R/I_G) as a function of temperature as an independent variable has good linear characteristics in the temperature range of 300–500 K. Due to the good responsiveness of multicolor luminescence to temperature, the hexagonal NaYF₄:Yb³⁺/Ho³⁺/Ce³⁺ with tunable morphology is a promising candidate for advanced temperature-responsive upconversion anti-counterfeiting. Our results provide a new pathway for the controllable synthesis of hexagonal NaYF₄ microcrystals as well as the regulation of upconversion luminescence that is excited by wavelengths other than 980 nm and its application in anti-counterfeiting.     

Spectroscopic investigations on Yb~(3+) doped and Pr~(3+)/Yb~(3+) codoped tellurite glasses for photonic applications

In this work we repo rt on structural and spect roscopic properties of Yb3+doped and Pr~(3+)/Yb~(3+)co-doped TeO_2-Bi_2 O_3-ZnO-Li_2 O-Nb_2 O_5(TBZLN) tellurite glasses.Bending and stretching modes of TeO_2 and Te-OH bond(strong and weak) were analysed from the deconvolution of observed Raman and FT-IR spectra.Based on the absorption measurements,the energy bands of Yb~(3+)and Pr~(3+)ions are assigned.The spectroscopic properties for the radiative transitions of Yb~(3+)and Pr~(3+)ions were reported using McCumber and Judd-Ofelt theories.Visible emission bands originating from ~3 P_1 and ~3 P_0 to lower lying levels of Pr~(3+)were registered under 447 nm excitation.The emission band around 1334 nm assigned to the Pr~3:~1 G_4→~3 H_5 was observed when excited at 980 nm.The stimulated emission cross-section(σ_(emi)(λ))and effective linewidth(Δλ_(eff)) for the ~3 P_1→~3 H_6,~3 P_1→~3 H_5,~3 P_0→~3 H_6,~3 P_0→~3 F_2,~3 P_1→~3 F_3,~3 P_1→~3 F_4,~3 P_0→~3 F_4 and ~1 G_4→~3 H_5 transitions of Pr~(3+)are reported.Upconversion luminescence in Pr~(3+)/Yb~(3+)codoped glass upon 980 nm excitation was measured.Possible resonant transfer processes between Yb~(3+)and Pr~(3+)ions are presented and discussed.The chromaticity co-ordinates were also evaluated from the visible emission spectra showing that Pr~(3+)/Yb~(3+)co-doped glass may be suitable for the development of yellow-orange(λ_(exc)=447 nm) and near white light(λ_(exc)=980 nm) emitting devices in photonics.     

Up-conversion luminescence of Er~（3＋）-doped and Yb~（3＋）/Er~（3＋） co-doped 12CaO·7Al_2O_3 poly-crystals

The optical properties of Er3+-doped and Yb3+/Er3+ co-doped 12CaO·7Al2O3 (C12A7) poly-crystals, synthesized by high temperature solid state method, were investigated in detail. For Er3+-doped and Yb3+/Er3+ co-doped C12A7 poly-crystals, two main emission bands centered around 530/550 nm (green) and 660 nm (red) were observed under 980 nm diode laser excitation via an up-conversion process. The intensity of green up-conversion emission had a strong increase in Er3+ (1.0 mol.%, 1.5 mol.%, 3.0 mol.%), and the intensity ratio of red to green up-conversion emission had an increase in Yb3+ (1.0 mol.%, 2.0 mol.%, 10. 0 mol.%)/Er3+ (fixed at 1.0 mol.%). This detailed study of the up-conversion processes allowed us to identify the dominant up-conversion mechanisms in Er3+-doped and Yb3+/Er3+ co-doped C12A7 poly-crystals.     

Y4GeO8:Er3+,Yb3+ up-conversion phosphors for optical temperature sensor based on FIR technique

Herein, we reported novel Y₄GeO₈:Er³⁺,Yb³⁺ phosphors elaborated via conventional solid-state reaction, and we further explored their properties as optical thermometer by using fluorescence intensity ratio (FIR) method complemented by detailed analysis on crystal structure, up-conversion luminescence and energy transfer from Yb³⁺ to Er³⁺. Upon 980 nm laser excitation, Y₄GeO₈:Er³⁺,Yb³⁺ phosphors present 525, 547 and 659 nm emission bands assigned to the characteristic transitions of Er³⁺. Furthermore, Y₄GeO₈:Er³⁺,Yb³⁺ samples show outstanding temperature sensing performances. To be specific, the minimal temperature resolution is 0.03 K (303 K), and the relative sensitivity of FIR can be up to 1.152%/K (303 K). Hence, Y₄GeO₈:Er³⁺,Yb³⁺ phosphors can be possible candidates for thermometry devices.     

Boosting single-band red upconversion luminescence in colloidal NaErF_4 nanocrystals:Effects of doping and inert shell

Single-band red upconversion luminescence(UCL) is vital to in vivo bioimaging as well as "see and treat" biomedicines. Herein, starting with the previously reported β-NaErF4:Tm UCNPs, we examined the effects of both Yb~(3+) doping and inert shell coating on the red-to-green(R/G) ratio for Er3+ based UCL. The doping of Yb~(3+) into the β-NaErF4:Tm3+ core not only enhances the whole UCL intensity, but also raises the R/G ratio by 1.25 times. In addition, the coating of an inert NaYF4 shell, which is usually adopted for the enhancement of UCL intensity, further boosts the R/G value up to as high as 77.92. This work may benefit the potential bioimaging application of single-band red UCL.     

Preparation and Characterization Upconversion Luminescence Material of Yttrium Aluminate Doped with Rare Earth

Low phonon energy yttrium aluminate was adopted as matrix and the upconversion materials yttrium aluminate co-doped with Yb³⁺ and Er³⁺ was synthesized by solid-state reaction method. The X-ray diffraction spectra and the upconversion emission spectra of various samples were measured and the effect of Er³⁺ concentration, sensitization, fluxing agent and calcining temperature on the luminescence properties was studied. Research results showed that the sample could emit green light at 543 and 570 nm when excited 980 nm laser; the optimum concentration of Er³⁺ should be 1.0%; sensitization of Yb³⁺ could enhance luminescent effects of Er³⁺ obviously; the optimum content of F₃BO₃ fluxing agent should be 8% and the optimum calcining temperature should be 1500 °C.     

Crystal growth,structure and laser performance of a new Yb~(3+):KBaY(MoO_4)_3 crystal

A Yb~(3+):KBaY(MoO_4)_3(Yb3+:KBYM) crystal with dimensions of 51 mm × 27 mm x 10 mm was successfully grown by the TSSG method.The characteristics of the crystal structure and probability of good optical properties were analyzed.The absorption and emission spectra of Yb3+:KBYM crystal exhibit broadened bands,with the maximum absorption cross-sections of 1.17 x 10~(-20),1.44 ×10~(-20) and 1.37 x 10-20 cm~2 at976 nm for X-,Y-and Z-polarizations,respectively.The corresponding absorption FWHMs are as wide as 77,46 and 55 nm.The well-known re-absorption effect of Yb3+in the crystal is discussed.Two methods,the Fiichtbauer-Ladenburg method(FL) and reciprocity method(RM) were adopted to compute the emission cross-sections and results show a certain discrepancy but the errors are allowable.The laser potentiality of the Yb3+:KBYM crystal was also evaluated by calculations of minimum inversion fraction β_(min),saturation pump intensity I_(sat),the minimum pump intensity I_(min) and gain cross-sections spectra.Laser experiment was carried out and Watt-level continuous wave laser has been realized.Results indicate that the Yb~(3+):KBYM crystal with a disordered structure may be a potential laser media that can be used to generate tunable and ultrashort pulse laser emissions with high quality beam.