Morphology control and temperature sensing properties of micro-rods NaLa(WO4)2:Yb3+,Er3+ phosphors

Uniform spindle-like micro-rods NaLa(WO₄)₂:Yb³⁺,Er³⁺ phosphors are prepared by the solvothermal method in the text. Controllable morphology of NaLa(WO₄)₂ crystal can be obtained by adjusting the prepared temperature, PH value, complexing agent content, and solvent ratio. Uniform NaLa(WO₄)₂:Yb³⁺,Er³⁺ micro-rods of 1.8 μm in length and 0.5 μm in width are synthesized at a low temperature of 120°C. The prepared NaLa(WO₄)₂:Yb³⁺,Er³⁺ phosphors present green upconversion luminescence under 980 nm excitation, luminescence intensity reaches to maximum at the Yb³⁺ and Er³⁺ concentration of 6 and 2 mol%. The temperature performance of the NaLa(WO₄)₂:Yb³⁺,Er³⁺ phosphors are evaluated based on thermal coupling technology. Temperature dependence of the two green emissions ratio of Er³⁺ ion is obtained, and the sensitivity of the sample can be calculated, the maximum sensitivity of NaLa(WO₄)₂:Yb³⁺,Er³⁺ is up to 0.019 K⁻¹ at the sample temperature of 564 K.     

High-accuracy dual-mode optical thermometry based on up-conversion luminescence in Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors

Due to the non-contact and high sensitivity, optical thermometry based on rare earth doped phosphors has been paid much attention to. Herein, dual-mode optical thermometers are designed using up-conversion luminescence of Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors, which were synthesized for the first time by high-temperature solid-state reaction method. The LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors exhibit reliable and excellent thermometric performance by combining fluorescence intensity ratio and decay lifetime for self-calibration. Specifically, the maximal relative sensitivities based on fluorescence lifetime were 0.27 %K⁻¹ and 0.33 %K⁻¹ for LaNbO₄:1Er³⁺:10Yb³⁺ and LaNbO₄:1Ho³⁺:10Yb³⁺ phosphors, respectively. The maximal relative sensitivity is 1.12 %K⁻¹ when using intensity ratio between thermal coupling energy levels in LaNbO₄:1Er³⁺:10Yb³⁺ as a detecting signal. Furthermore, the maximal relative sensitivity reaches as high as 0.98 %K⁻¹ when taking advantage of special non-thermal coupling energy levels in LaNbO₄:1Ho³⁺:10Yb³⁺. These results indicate that Er³⁺/Ho³⁺-Yb³⁺ doped LaNbO₄ phosphors possess great potential in self-calibrated optical thermometric techniques.     

Multifunctional optical thermometry based on the stark sublevels of Er3+ in CaO-Y2O3: Yb3+/Er3+

A conventional high temperature solid state method was utilized to prepare CaO-Y₂O₃, which is a potential candidate for manufacturing crucible material to melt titanium and titanium alloys with low cost. Meanwhile, Yb³⁺ ions and Er³⁺ ions were selected as the sensitizers and activators respectively to dope into CaO-Y₂O₃, aimed at providing real-time optical thermometry during the preparation process of titanium alloys realized using fluorescence intensity ratio (FIR) technology. The results reveal that a high measurement precision can be acquired by using the Stark sublevels of Er^{3+ 4}F_9/2 to measure the temperature with a maximum absolute error of only about 3 K. In addition, by analyzing the dependence of ⁴I_13/2 → ⁴I_15/2 transition on pump power of 980 nm excitation wavelength, it was found that the laser-induced thermal effect has almost no influence on the temperature measurement conducted by using the FIR of the Stark sublevels of Er^{3+ 4}I_13/2, which means that a high excitation pump power can be used to obtain strong NIR emission and good signal-to-noise ratio for optical thermometry without the influence of the laser-induced thermal effect. All the results reveal that CaO-Y₂O₃: Yb³⁺/Er³⁺ is an excellent temperature sensing material with high measurement precision.     

高价氧化物对掺铒碲酸盐玻璃光谱性质的影响

对比分析了相同铒离子低掺杂浓度下,Y2O3、GeO2、Nb2O5 WO3四种高价氧化物对碲锌玻璃系统光谱性质的影响.测试了四个样品的红外透过光谱,结果表明由于Nb2O5 、WO3二者引入的高价阳离子的极化作用使得二者部分的充当玻璃形成体的角色,使得玻璃的有效红外透过范围降低.同时吸收光谱也表明这两种高价氧化物会使得玻璃紫外吸收边发生明显红移.铒离子的近红外荧光光谱结果表明,引入高价氧化物会由于高价阳离子的极化作用导致铒离子的荧光半高宽增加,特别以含WO3的TZW样品具有最高的荧光半高宽达64nm.     

Multicolor upconversion emission and highly optical temperature sensing based on lanthanide-doped double perovskite Sr2LaNbO6 phosphors

Here we adopt trivalent lanthanide (Ln³⁺ = Er³⁺, Er³⁺/Ho³⁺, and Yb³⁺/Tm³⁺) doped Sr₂LaNbO₆ (SLNO) as novel upconversion luminescence (UCL) materials for achieving UCL and optical temperature sensing under 980 nm excitation. Specifically, Er³⁺ single doped Sr₂LaNbO₆ phosphors present bright high-purity green emission under the 980 nm excitation. While co-doping with the Ho³⁺ ions, the component of red emission from Er³⁺ ions increases significantly and sample show a remarkable enhancement of luminescent intensity relative to SLNO:Er³⁺ sample. The above-mentioned phosphors and Yb³⁺/Tm³⁺ co-doped phosphor (blue emission) successfully achieve high-purity trichromatic UCL and mixed white light output in the same host. Furthermore, the temperature sensing performance of the SLNO:Er³⁺/Ho³⁺ phosphor based on the fluorescence intensity ratio (FIR) is systematically studied for the first time. The temperature sensing based on the non-thermal coupling levels (NTCLs) exhibit higher sensitivity than that based on the thermal coupling levels (TCLs). The maximum absolute and relative sensitivity for ⁴F_9/2/⁴I_9/2 NTCLs reach 0.16803 K^?1 at 427 K and 0.01591 K^?1 at 641 K, respectively. Interestingly, NIR emission of ⁴I_9/2 → ⁴I_15/2 transition presents a thermal enhancement, while visible emissions show thermal quenching. These results indicate that the Ln³⁺ doped Sr₂LaNbO₆ UCL phosphors have potential applications in the fields of non-contact temperature sensors, full-color displays, and anti-counterfeiting.     

Tunable multicolor upconversion luminescence of Yb3+ sensitized Na3La(VO4)2 crystals

Multicolor upconversion luminescence materials show significantly applications in materials science. In this paper, the novel Yb³⁺-sensitized Na₃La(VO₄)₂ upconversion luminescence crystals are synthesized by the solid-state reaction method. Three primary colors upconversion luminescence are successfully achieved in Na₃La(VO₄)₂:Yb³⁺,Tm³⁺, Na₃La(VO₄)₂:Yb³⁺,Er³⁺, and Na₃La(VO₄)₂:Yb³⁺,Ho³⁺ crystals excited by the single 980 nm LD. Multicolor upconversion luminescence can be obtained by simply adjusting the combination ratios of these three samples. Luminescence mechanisms of the Yb³⁺-sensitized system are discussed in detail. In the Na₃La(VO₄)₂ host material, the Yb³⁺/Ho³⁺ codoped system exhibits unusual red upconversion luminescence based on the short decay time of Ho³⁺ ion ⁵I₆ level, which provides the possibility of three primary color luminescence under 980 nm excitation.     

Optical transition and luminescence properties of Sm3+-doped YNbO4 powder phosphors

A series of YNbO₄: Sm³⁺ powder phosphors with different doping concentrations were synthesized by a traditional high-temperature solid-state reaction method. The crystal structure of the obtained samples was characterized by means of X-ray diffraction. Concentration quenching, energy-transfer mechanism, and luminescence thermal stability of YNbO₄: Sm³⁺ samples were studied through the fluorescence spectra and decays. It was concluded that electric dipole-dipole interaction was the dominant energy-transfer mechanism between Sm³⁺ ions according to both Van Uitert's model and Dexter's model. Using the Arrhenius model, crossover process was proven to be responsible for the luminescence thermal quenching of Sm³⁺. Moreover, a novel approach for evaluating the optical transition properties of Sm³⁺ ion in YNbO₄ powders using the diffuse-diffraction spectrum and fluorescence decay was examined in the framework of Judd-Ofelt (J-O) theory. It was confirmed that the J-O parameters Ω_λ (λ = 2, 4, 6) of Sm³⁺ in YNbO₄ powder were reliable by comparing the radiation transition rate with the measured emission results.     

Enhanced near-infrared to green upconversion from Er3+-doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

In this work, effect of glass composition as well as ceramization on visible and near-infrared (NIR) luminescence properties along with their decay dynamics of Er³⁺ ions has been compared considering two different oxyfluoride glasses yielding BaF₂ and BaGdF₅ nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium-(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er³⁺ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited-state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground-state ⁴I_15/2 to the excited-state ⁴I_11/2 followed by ESA of second photon to the ⁴F_7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.     

Near infrared light-induced photocurrent in NaYF4:Yb3+, Er3+/WO2.72 composite film

Spectral conversion technology based on NaYF₄:Yb³⁺, Er³⁺ upconversion nanoparticles was extensively used to improve photovoltaic conversion efficiency of solar cells. However, the response mismatch between absorption of semiconductors and upconversion luminescence (UCL) limits the application of spectral conversion technology. Nonstoichiometric WO_2.72 nanoparticles display the broad absorption from visible to near-infrared region due to the presence of oxygen vacancy, which is overlapped with the UCL of NaYF₄:Yb³⁺, Er³⁺ nanoparticles. Thus, the combination between NaYF₄:Yb³⁺, Er³⁺ nanoparticles, and nonstoichiometric WO_2.72 provides a possibility for designing a novel UCL spectral converted solar cells. In this work, composite film consisted of NaYF₄:Yb³⁺, Er³⁺ nanoparticles, and WO_2.72 nanofibers was prepared. The UCL of NaYF₄:Yb³⁺, Er³⁺/WO_2.72 film was decreased in contrast to pure NaYF₄:Yb³⁺, Er³⁺ nanoparticles due to energy transfer from NaYF₄:Yb³⁺, Er³⁺ nanoparticles to WO_2.72 nanofibers. The NaYF₄:Yb³⁺, E³⁺/WO_2.72film exhibits the photocurrent generation upon the 980 nm excitation. This novel UCL spectral converted solar cells based on the broad absorption of defects in the WO_2.72 host will provide a novel view for photovoltaic devices.     

Power dependent upconversion in Er3+/Yb3+ co-doped BiNbO4 phosphors

In the present article, optical properties and energy upconversion in Er³⁺/Yb³⁺ co-doped BiNbO₄ matrix were investigated. The BiNbO₄ matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix shows that the crystal structure is consistent with ICSD code 74338. The grain distribution and the behavior of doping with Er³⁺ and Yb³⁺ on the sample surface were obtained by scanning electron microscope. Raman spectral characterization was carried out to examine the behavior of the vibrational modes of the samples. Upconversion emissions in the visible region at 484.5, 522, 541.5 and 670.5 nm in the matrices BiNbO₄:Er,Yb and BiNbO₄:Er were observed and analyzed as a function of 980 nm laser excitation power and rare-earth doping concentration. The results show that BiNbO₄ is a promising host material for efficient upconversion phosphors.     

Enhancing upconversion luminescence and thermal sensing properties of Er/Yb co-doped oxysulfide core-shell nanocrystals

The development of noncontact thermal probe based on stable inorganic materials of trivalent lanthanide (Ln³⁺) doped phosphors with nontoxicity is of vital importance for their promising applications in bio-medical fields. Here we explore the upconversion luminescence and thermal sensing properties of Er³⁺, Yb³⁺ co-doped oxysulfide in a broad temperature range of 300-583 K. It was found that constructing an active shell with an optimum concentration of sensitizers is an efficient way to improve both the luminescent intensities and thermal sensitivity. Compared with the core-only sample, the luminescent intensity of the Y₂O₂S: Er³⁺, Yb³⁺@ Y₂O₂S: 5%Yb³⁺ sample is significantly enhanced by 12-fold at excitation of 980 nm. While further increasing the Yb³⁺ concentration in the shell activates new quenching pathways of Er³⁺ → Yb³⁺ → quencher from the core to the shell. Similar quenching mechanisms are also observed at excitation of 1550 nm. These energy transfer processes and luminescence mechanisms are verified in the fluorescence decay measurements. Furthermore, coating the core sample with an active shell doped by 10% Yb³⁺ enhances the thermal sensitivity by 30%, holding a high and stable sensitivity more than 50 × 10⁻⁴ K⁻¹ in a broad temperature range of 423-573 K at 980 nm excitation. In addition, at the much safer excitation wavelength of 1550 nm, this sample achieved the maximum sensitivity of 45 × 10⁻⁴ K⁻¹ at 503 K. Our work contributes a feasible and versatile way to promote the luminescence and thermal sensing properties of Ln³⁺-based materials, combining with the nontoxic oxysulfide host, indicating their potential applications as safe fluorescent and temperature nano-probes in bio-field.     

Enhanced upconversion luminescence and optical temperature sensing performance in Er3+ doped BaBi2Nb2O9 ferroelectric ceramic

A series of BaBi_2-xNb₂Er_xO₉ ceramic compositions with different Er³⁺ concentration (x = 0.0–8 mol %) is synthesized by a conventional solid-state reaction method. The upconversion (UC) light emission under 980 nm excitation with different pump powers and luminescence-based temperature sensing ability of BaBi_2-xNb₂Er_xO₉ composition have been examined. The formation of a Bi-layered perovskite phase of BaBi₂Nb₂O₉ is confirmed having an orthorhombic geometry and Fmmm space group. Shifts in the Raman modes indicate reduced interaction of Bi³⁺ ions with NbO₆ octahedron leading to relaxation of structural distortion with increasing Er³⁺ content. The maximum value for remnant polarization and coercive field of doped BaBi_2-xNb₂Er_xO₉ ceramic for (x = 0.08) Erbium concentration comes out to be 2.9524 μC/cm² and 49.8980 kV/cm. For an optimum content of x = 0.04, two strong UC green emission bands were observed at 549 nm via ⁴S_3/2 → ⁴I_15/2 transition and 527 nm via ²H_11/2 → ⁴I_15/2 transitions, and a weak red emission appears at 657 nm attributed to the ⁴F_9/2 → ⁴I_15/2 transition. Pump power dependence suggests that UC emission is a two-photon mechanism for red and green emission bands. Temperature sensing evaluated by the change in the fluorescence intensity ratio (I₅₂₇/I₅₄₉) indicates the highest sensitivity to be 0.00996 K^?1 at 483 K for an optimum concentration of Er³⁺ at x = 0.04 in BaBi_2-xNb₂Er_xO₉ composition and is useful for non-contact optical thermometry.     

Sm3+掺杂GdVO4荧光材料的制备及其上转换发光性能

以水热法制备GdVO4:Sm3+上转换发光材料,表征了其形貌,考察了Sm3+掺杂量、焙烧温度及乙二胺四乙酸二钠(EDTA)掺杂量对材料上转换发光性能的影响. 结果表明,所制材料为四方晶系,在816 nm近红外光激发下,Sm3+掺杂量1.5%(mol)、焙烧温度800℃、EDTA:Sm3+(摩尔比)为1:1时,其上转换发光性能最好,发射峰位于565, 604, 647和706 nm处,分别归属于Sm3+的4G5/2→6HJ (量子数J=5/2, 7/2, 9/2, 11/2)电子跃迁,材料有可能用作LED灯荧光粉.     

Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Designing dual-mode luminescence in Er3+ doped Y2WO6 microparticles for anticounterfeiting and temperature measurement

In recent years, rare earth ions doped optical materials have been extensively utilized in anticounterfeiting, temperature measurement, and other fields. However, it is difficult for single-mode photoluminescence to meet the increasingly complex anticounterfeiting needs in practice. In this article, Yb³⁺/Er³⁺ codoped Y₂WO₆ multifunctional microparticles have been designed and prepared, which can emit multimode luminescence and are used for anticounterfeiting and temperature measurement. Under excitation at 254, 365, and 980 nm, Y₂WO₆:Yb³⁺/Er³⁺ microparticles can emit blue, green, and yellow-green luminescence, respectively. The multicolor emission is helpful to improve the security of anticounterfeiting in multimode. In addition, the upconversion, downconversion luminescence, and downconversion lifetime attenuation of this material can be used for fast responsive and noncontact temperature measurement. Among the three temperature measurement methods, the material has the highest sensitivity under the downconversion temperature measurement method, which is 1.25 × 10^–2 K^–1 (at 303 K). The results suggest that the Y₂WO₆:Yb³⁺/Er³⁺ microparticles have excellent applications in the domain of multimode anticounterfeiting and temperature measurement.     

Scalable synthesis of ytterbium and erbium codoped calcium molybdate phosphors as upconversion luminescent thermometer

Luminescent thermometry is a noninvasive method of temperature detection with high sensitivity and response speed. The present study demonstrated the process-intensified synthesis of ytterbium and erbium codoped calcium molybdate phosphors (CaMoO₄:Yb³⁺/Er³⁺). The experiment involved the initial premixing of the precursors using a high-gravity rotating packed bed (RPB) reactor and subsequent calcination processing. The pronounced mass transfer and micromixing of the reactants in the RPB facilitated the scalable and controllable synthesis of CaMoO₄:Yb³⁺/Er³⁺ particles with submicron sizes and regular morphologies. The CaMoO₄:Yb³⁺/Er³⁺ particles exhibited a bright-green emission with temperature-dependent luminescence characteristics under 980 nm laser irradiation. Furthermore, the maximum absolute sensitivity was determined to be 0.02837 K⁻¹. These results indicated that the synthesized product was a suitable candidate for application in upconversion luminescent thermometers capable of temperature sensing at the microscale.     

The upconversion luminescence modulation and its enhancement in Er3+‐doped Na0.5Bi0.5TiO3 based on photochromic reaction

A large and reversible upconversion (UC) luminescence modulation has been found in the Na_0.498Bi_0.498TiO₃:0.002Er (NBT:0.002Er) based on the photochromic reaction. The dependence of luminescence modulation of the ceramics on the wavelength of irradiation light and sintering temperature was investigated. It was found that the optimized sintering temperature and irradiation wavelength were 1130°C and 405 nm, respectively. The highest ΔR_t (defined as: ΔR_t = (R₀ – R_t)/R₀×100(%), where R₀ and R_t are the initial emission intensity and that after different irradiation time, respectively) value of 44.9% was obtained for the ceramics sintered at 1130°C after irradiation at 405 nm. More importantly, for the poled ceramics, ΔR_t value was promoted to a high value of 75.5%, which was 168% of that of the unpoled ones. The mechanism of luminescence modulation and its enhancement via electric field poling were discussed. This study demonstrated that electric field poling was an effective strategy to enhance the PC reaction in the NBT ceramics.     

Hydrothermal formation and up‐conversion luminescence of Er3+‐doped GdNbO4

The effect of concentration of Er³⁺ on the up‐conversion and photoluminescence properties of Gd_1.00?xEr_xNbO₄, x=0‐0.50 which has monoclinic fergusonite‐type structure as a main phase has been investigated, using a processing technique based on hydrothermal method. Under weakly basic hydrothermal condition at 240°C for 5 hours, a single phase of fergusonite‐type Gd_1.00?xEr_xNbO₄ solid solution was directly formed as nanocrystals by the substitutional incorporation of Er³⁺ into GdNbO₄ because of the gradual and linear decrease in the lattice parameters of the monoclinic phase corresponding to the Vegard's Law. The gadolinium niobate doped with 2 mol% Er³⁺, Gd_0.98Er_0.02NbO₄ after heating at 1300°C for 1 hour, which has nanocrystalline structure whose crystallite size is around 29 nm, exhibits the highest photoluminescence intensity in the green spectral region, 515‐560 nm under excitation at wavelength of 254 nm. On the other hand, the up‐converted luminescence intensity of the niobate nanocrystals becomes the maximum at the concentration of 20 mol% Er³⁺, Gd_0.80Er_0.20NbO₄ under excitation at 980 nm. These results demonstrate that the material, Er³⁺‐doped GdNbO₄ nanocrystals prepared through hydrothermal route and postheating has potential for up‐converting phosphor.     

基于上转换发光的可见/近红外光催化研究现状及展望

上转换发光材料可将低能光子转换为高能光子,对于太阳能的转化利用具有潜在的应用前景。本文以TiO₂为例,介绍了上转换发光在可见/近红外光催化领域的研究背景,说明了光能吸收、光能转换、光能转移、表面反应的光能利用机制,总结了上转换发光的研究进展。同时重点分析了稀土上转换发光在可见/近红外光催化领域的研究现状,阐述了上转换发光与其它改性方法协同提高TiO₂光催化效率的基本原理。最后提出了基于复合上转换发光的光催化研究思路,展望了上转换发光在光催化中的应用前景。     

La2O2SO4:RE/Yb new phosphors for near infrared to visible and near infrared upconversion luminescence (RE=Ho,Er, Tm)

The 3 new upconversion (UC) phosphors of La₂O₂SO₄:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE³⁺ size, confirming the direct crystallization of solid solution. The Er³⁺ and Ho³⁺ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm³⁺ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its ³H₄ → ³H₆ transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated.