Broadband downconversion in YVO4：Tm3＋,Yb3＋ phosphors

An efficient near-infrared (NIR) downconversion (DC) by converting broadband ultraviolet (UV) into NIR was demonstrated in YVO4:Tm3+,Yb3+ phosphors. The phosphors were extensively characterized using various methods such as X-ray diffraction, photoluminescence excitation, photoluminescence spectra and decay lifetime to provide supporting evidence for DC process. Upon UV light varying from 260 to 350 nm or blue light (473 nm) excitation, an intense NIR emission of Yb3+ corresponding to transition of 2F5/2→2F7/2 peaking at 985 nm was generated. The visible emission, the NIR mission and the decay lifetime of the phosphors of various Yb3+ concentrations were investigated. Experimental results showed that the energy transfer from vanadate group to Yb3+ via Tm3+ was very efficient. Application of the broadband DC YVO4:Tm3+,Yb3+ phosphors might greatly enhance response of siliconbased solar cells.     

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.     

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...     

Energy transfer and luminescent properties of Tb3+ and Tb3+, Yb3+ doped CNGG phosphors

In this work,calcium niobium gallium garnet(Ca₃ Nb_1.6875Ga_3.1875O₁₂-CNGG) ceramic samples singledoped with Tb³⁺ and co-doped with Tb³⁺ and Yb³⁺ ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb³⁺ ions corresponding to the maximum luminescence in the green spectral range in CNGG:...     

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....     

A NIR to NIR rechargeable long persistent luminescence phosphor Ca2Ga2GeO7:Yb3+,Tb3+

Near infrared to near infrared (NIR–NIR) photo-stimulated persistent luminescence (PSPL) has shown excellent potential in high-resolution bioimaging for deep tissues. However, the PSPL in NIR-Ⅱ region (900–1700 nm) is still lacking. In this work, Ca₂Ga₂GeO₇:Yb³⁺,Tb³⁺ (CGGYT) phosphor with unique low-dimensional crystal structure was synthesized by high-temperature solid–state reaction. Thanks to the carriers transferring from deep traps to shallow ones induced by low energy light, the 978 nm PSPL originating from ²F_5/2 to ²F_7/2 transition of Yb³⁺ induced by multimode stimulating (980 nm or WLED) is successfully realized after pre-excited by UV lamp. The NIR PSPL of the specimen can be repeatedly stimulated after placed in dark for 12 h. Moreover, the results indicate that codoping with Tb³⁺ can significantly enhance the NIR-II PSPL owing to the quantum cutting persistent energy transfer (QC PET) from Tb³⁺ to Yb³⁺. Our study points to a new direction for the future development of multimode PSPL materials for bioimaging or multimode optical storage applications.     

Increased downconversion efficiency and improved near infrared emission by different charge compensations in CaMoO_4：Yb~（3＋） powders

All of the samples were synthesized by sol-gel methods.Two approaches to charge compensation,(i) 2Ca2+→Yb3++M+,where M+ is an alkali ion like Li+,Na+ and K+,and(ii) indirect charge compensation:3Ca2+→2Yb3++vacancy,were studied in detail.It was found that charge compensation would be very beneficial for the growth of the grains,especially in Li+ ions added samples.All the grains were homogeneously spherical with less boundaries;in addition,a great variety of the absorption ability in different charge compens...     

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.     

Effects of Bi3+ on down-/up-conversion luminescence,temperature sensing and optical transition properties of Bi3+/Er3+ co-doped YNbO4 phosphors

A series of YNbO₄:Bi³⁺ and YNbO₄:Bi³⁺/Er³⁺ phosphors were prepared by a conventional high temperature solid–state reaction method. The results of XRD and Rietveld refinement confirm that monoclinic phase YNbO₄ samples are achieved. The down-/up-conversion luminescence of Er³⁺ ions was investigated under the excitation of ultraviolet light (327 nm) and near infrared light (980 nm). Under 327 nm excitation, broad visible emission band from Bi³⁺ ions and characteristic green emission peaks from Er³⁺ ions are simultaneously observed, while only strong green emissions from Er³⁺ ions are detected upon excitation of 980 nm. Remarkable emission enhancement is observed in down-/up-conversion luminescence processes by introducing Bi³⁺ ions into Er³⁺-doped YNbO₄ phosphors. Pumped current versus up-conversion emission intensity study shows that two-photon processes are responsible for both the green and the red up-conversion emissions of Er³⁺ ion. Through the study of the temperature sensing property of Er³⁺ ion, it is affirmed that the temperature sensitivity is sensitive to the doping concentration of Bi³⁺ ions. By comparing the experimental values of the radiative transition rate ratio of the two green emission levels of Er³⁺ ions and the theoretical values calculated by Judd-Ofelt (J-O) theory, it is concluded that the temperature sensing property of Er³⁺ ions is greatly affected by the energy level splitting.     

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.     

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...     

Yellow upconversion luminescence in Ho3＋/yb3＋ co-doped Gd2Mo3O9 phosphor

The strong yellow upconversion (UC) light emission was observed in Ho3+/Yb3+co-doped Gd2Mo3O9 phosphor under the excitation of 980 nm diode laser. The phosphors were synthesized by the traditional soli...     

Cr3+/Y3+ co-doped persistent luminescence nanoparticles with biological window activation for in vivo repeatable imaging

The near-infrared(NIR) persistent luminescence materials(PLMs) can remain long-lasting luminescence after removal of the excitation light,which permits bioimaging with high sensitivity owing to the absence of background fluorescence interference from in situ excitation.Recently,the NIR PLMs have aroused intensive research interest in bioimaging.However,the optimal excitation wavelength of current NIR PLMs is located in the ultraviolet region with shallow tissue penetration,making it difficult to...     

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.     

Insights into structural and spectroscopic characterization of Sm3+ doped orange rich red emitting CsMgPO4 phosphors

In the present study, Sm³⁺ activated inorganic orthophosphate CsMgPO₄ (CSMP) phosphors were prepared by adopting a solid-state reaction method. The structural phase purity and morphological features were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. The molecular structure and vibrational modes were substantiated with the Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy characterization. The optical bandgap of the host and Sm³⁺ doped phosphors was deduced from the diffused reflectance (DR) spectra with a typical value of 5.72 eV and a small variation is observed with increasing concentrations. A systematic study of photoluminescence (PL) properties of Sm³⁺ doped CSMP phosphors was carried out. From the room temperature excitation and emission spectra, it is found that the phosphor emits in the orange rich red light under the suitable excitation of 402 nm in the UV region and concentration quenching occurs at x = 0.02 doping level. The emission peaks observed at around 562, 598 and 644 nm confirm the characteristic Sm³⁺ 4f-4f transitions. The temperature-dependent photoluminescence (TD-PL) of the x = 0.02 (optimum doping) is recorded from 30 to 210 °C, showing good thermal stability even at 150 °C. The thermal quenching mechanisms are discussed based on the configuration coordinate model of excitation and emission. The prepared phosphors are found to exhibit near thermal stability compared to the commercially available red phosphors. PL decay time and quantum efficiency were measured. The colour coordinates are found to lie in the orangish-red region of the colour space. Thus the prepared phosphors CSMP:x Sm³⁺ can be useful as a red component in designing UV excitable chip-based phosphor-converted white LED applications.     

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.     

Plasmon-enhanced broad-band quantum-cutting of NaBaPO4:Eu2+,Er3+ phosphors with silver nano-particles

NaBaPO₄:Eu²⁺,Er³⁺ phosphors and Ag nano-particles (NPs) were prepared by the solid-state reaction and chemical reduction method, respectively. The fluorescence spectra and decay curves demonstrate the effective energy transfer from Eu²⁺ to Er³⁺ and the existence of three-photon quantum-cutting through two-step cross-relaxation of Er³⁺. The quantum-cutting emission is peaked at 1534 nm with a broad excitation band centered at 352 nm. Plasmon-enhanced quantum-cutting of NaBaPO₄:Eu²⁺,Er³⁺ phosphors was realized by decorating Ag NPs. The largest enhancement factor is 1.395. It is hopeful to improve the photovoltaic conversion efficiency of Ge solar cells by using this phosphor.     

Synthesis and optical properties of novel apatite-type NaCa3Bi(PO4)3F:Dy3+ yellow-emitting fluorophosphate phosphors for white LEDs

In this study, novel yellow-emitting fluorophosphate NaCa₃Bi(PO₄)₃F phosphors doped with different concentrations of Dy³⁺ ions were first obtained via high-temperature solid-state reaction. The crystal structure, phase purity, particle morphology, photoluminescence (PL) properties, thermal stability, and luminescence decay curves of the resulting phosphors were then characterized in detail. Under the excitation of 349 nm, the three dominant peaks of the NaCa₃Bi(PO₄)₃F:Dy³⁺ are centered at 480 nm (⁴F_9/2-⁶H_15/2), 577 nm (⁴F_9/2-⁶H_13/2), and 662 nm (⁴F_9/2-⁶H_11/2). The optimal doping concentration of Dy³⁺ ions in the NaCa₃Bi(PO₄)₃F:xDy³⁺ phosphors is x = 5 mol%. The phosphors show excellent thermal stability with high activation energy (E_a = 0.32 eV). Eventually, the synthesized white light-emitting diode (w-LED) demonstrates the Commission International de L'Eclairage (CIE) chromaticity coordinates of (0.341, 0.334), a good correlated color temperature (CCT) of 5083 K, and a high color rendering index (R_a) of 92. Revealing its potential as yellow-emitting phosphors, the feasibility of the fabricated apatite-type NaCa₃Bi(PO₄)₃F:Dy³⁺ fluorophosphate phosphors was confirmed for w-LEDs.     

Zirconium metal organic framework for design of tetragonal rare earth-doped zirconia nanoparticles

Zirconium metal–organic frameworks ZrOBDC (where BDC = C₆H₄(COOH)₂, terephthalic acid) doped and co-doped with rare earth ions Ln (ZrOBDC:Ln³⁺, where Ln³⁺ = Eu³⁺ and Tb³⁺ as well as Er³⁺ and Yb³⁺) were used as precursors for the design of tetragonal rare earth doped zirconia nanoparticles (t-ZrO₂:Ln³⁺ NPs) through annealing process. Preparation, characterization and luminescence properties of ZrOBDC:Ln³⁺ and ZrO₂:Ln³⁺ NPs were investigated. The as-obtained t-ZrO₂:Ln³⁺ NPs have high purity with an average size of 20–30 nm. The luminescence spectra of ZrOBDC:Tb³⁺ and ZrOBDC:Eu³⁺ display strong green and red emission at around 544 and 611 nm which correspond to ⁵D₄ → ⁷F₅ and ⁵D₀ → ⁷F₂ transitions of Tb³⁺ and Eu³⁺ ions, respectively. The green and red up-conversion emissions of ZrO₂:Er³⁺,Yb³⁺ NPs due to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of the Er³⁺ ions are observed under 976 nm laser excitation.     

A novel blue-light excitable Pr3+ doped(Sr,Ba)LaMgTaO6 phosphor for plant growth lighting

In this work,a series of Pr³⁺ ions doped(Sr,Ba)LaMgTaO₆ phosphors were prepared and applied for plant growth lighting.Under 450 nm excitation,(Sr,Ba)LaMgTaO₆:Pr³⁺ exhibits intense reddish emission at around 650 nm which is assigned to the ³p₀→³F₂ transition of Pr³⁺ ions.The luminescence intensity reaches to the maximum at 2.5 mol% Pr³⁺ doping content both in SrLaMgTaO₆:Pr^...