Fabrication and characterization of up-converting β-NaYF4:Er3+,Yb3+@NaYF4 core–shell nanoparticles for temperature sensing applications

Abstract

this paper presents the use of soft template method to synthesize core and core-shell up-converting nanoparticles usefull for temperature sensing applications. Based on the stock solutions of core β-NaYF 4 :er 3+ ,Yb 3+ nanoparticles and involving soft template method without any additional process of surface functionalization, it is possible to directly design the core-shell β-NaYF 4 :er 3+ ,Yb 3+ @naYf 4 nanoparticles, which can be perfectly dispersed in cyclohexane and surfactants like oleic acid (oA), triethanolamine (teA) or cetyltrimethylammonium bromide (ctAB). the morphological, crystalline and elemental characteristics of samples were investigated by field emission Scanning electron Microscopy, X-Ray Diffraction, High Resolution Transmission Electron Microscopy, Selected Area Electron Diffraction patterns and Energy-Dispersive X-Ray Spectroscopy (EDX) measurements. The results showed that the synthesized naYf 4 :er 3+ ,Yb 3+ @naYf 4 core-shell nanoparticles have roughly spherical shape, pure hexagonal β phase with core size of about 35 ± 5 nm and shell thickness of about 40 ± 5 nm. It has been shown that the coating of the β-NaYF 4 :er 3+ ,Yb 3+ core with naYf 4 shell layer enables to enhance the green upconversion (Uc) emission intensities in respect to red one. Under 976 nm excitation, the synthesized β-NaYF 4 :2%Er 3+ ,19%Yb 3+ @naYf 4 core-shell nanoparticles revealed three strong emission bands at 520 nm, 545 nm and 650 nm corresponding to 2 H 11/2 , 4 S 3/2 and 4 f 9/2 to 4 i 15/2 transitions of er 3+ ions with the lifetimes of 215, 193 and 474 µs, respectively. The calculated cie chromaticity coordinates proved that the emission colour of core-shell nanoparticles was changed from red into yellowish green upon increasing the power density of the 976 nm laser from 0.73 to 9.95 W/cm 2. The calculated slopes indicated that in the β-NaYF 4 :2%Er 3+ ,19%Yb 3+ @naYf 4 core-shell nanoparticles, two-photon and three-photon Uc processes took place simultaneously. Although the former one is similar as in the case of β-NaYF 4 :er 3+ ,Yb 3+ bare core nanoparticles, the latter one, three-photon Uc process for green emission occurs, due to cross relaxation processes of two er 3+ ions only within nanoparticles with core-shell architecture. Moreover, the energy difference between the 2 H 11/2 and 4 S 3/2 levels and associated constant of naYf 4 @naYf 4 host lattice were determined and they reached ~ 813 cm −1 and 14.27 (r 2 = 0.998), respectively. In order to investigate the suitability of nanoparticles for optical temperature sensing, the emission spectra were measured in a wide temperature range from 158 to 298 K. An exceptionally high value of relative sensitivity was obtained at 158 K and it amounted to 4.25% K −1. further temperature increase resulted in gradual

Enhancing upconversion via constructing local energy clusters in lanthanide-doped fluoride nanoparticles

“…The S a and S r can be fitted by the following equations: 39–41 Compared with the 20Yb/2Er:NaGdF 4 NPs, the calculated S a values of the 20Yb/8Er/20Ca:NaGdF 4 NPs were greatly increased in the whole measured temperature range (Fig. 5e), and the S r values were also improved in the range of 330–583 K (Fig.…”

Strong green upconversion emission from submicron spindle-shaped SrMoO4:Yb3+,Er3+

“…ing temperature as the SMO lattice structure is already optimized for UCL emission after being annealed for 6 h. The NaYF 4 :20%Yb/3%Er sample showed characteristic behavior according to the most reported literature. [53][54][55] According to studies for bulk NaYF 4 :Yb,Er at low temperature (i.e., below room temperature), energy transfer was efficient for 2 H 11/2 and 4 S 3/2 energy levels, and therefore an increase in green emission was observed. [53][54][55] However, with the thermal quenching temperature along with the lattice structure variation taking place, eventually it decreased.…”

Excitation Mechanism Rearrangement in Yb3+-Introduced La2O2S:Er3+/Polyacrylonitrile Photon-Upconverted Nanofibers for Optical Temperature Sensors

“…Among RE ions, the thermometric properties of Er 3+ have been widely inspected owing to its intense green UC emissions arising from TCLs with appropriate Δ E values. − Nevertheless, the failure of Er 3+ to efficiently absorb near-infrared (NIR) light leads to relatively poor UC emission performance, and thus, the signal of sensors is not being captured accurately. − A radical strategy should therefore be proposed to improve the UC behavior. Yb 3+ is considered a promising sensitizer, as it can efficiently absorb NIR light, not only bringing strong UC emissions but also maintaining the temperature-sensing capability of Er 3+ . − Many research studies established rate equation models to describe the UC mechanism of Er 3+ /Yb 3+ , facilitating further exploration of the essence of optical temperature sensors. − Additionally, the selection of host materials significantly affects the luminescence performance and temperature-sensing capability of fluorescent thermometers. − Sulfur oxides have been extensively investigated as host materials with large band gaps, low phonon energy, and stable thermochemical properties, offering great potential in optical temperature sensing. − However, the limitations of NCs are high molding consumption, constant shape, and challenging recycling.…”