Exploring the Phase‐Selective, Green, Hydrothermal Synthesis of Upconverting Doped Sodium Yttrium Fluoride: Effects of Temperature, Time, and Precursors

Abstract

The aim of this work was i) to develop ah ydrothermal, low-temperature synthesis protocola ffording the upconverting hexagonal phaseN aYF 4 with suitable dopants while adhering to the "green chemistry" standards and ii)to exploret he effect that different parameters have on the products. In optimizingt he synthesis protocol, short reaction times andl ow temperatures (below 150 8C) were considered. Yb 3 + and Er 3 + ions were chosen as dopants for the NaYF 4 material. Within the context of the second goal, parameters including nature of the precursors, treatment temperature, and treatment time were investigatedt oa fford ap ure hexagonal crystalline phase, both in the dopeda nd undoped materials. To fully explore the synthesis results, the prepared materials were characterized from as tructural (XRD),c ompositional (XPS, ICP-MS), and morphological (SEM) point of view.T he upconverting properties of the compounds were confirmed by photoluminescence measurements.[a] N.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.

Th4+ Co‐doped YF3 : Yb3+, Er3+ Nanostructures for Enhanced Visible and NIR‐II Emissions and Potential Application as Cryogenic Thermometer

“…For the UC emissions under a 980 nm laser excitation, the possible pathways are: ground state absorption (GSA), excited state absorption (ESA), energy transfer (ET), cross‐relaxation (CR), and multi phonon relaxations (MPR) (Figure 4d). [9] The Yb 3+ ions initially present in ground state ( 2 F 7/2 ), are excited to 2 F 5/2 state on pumping by a 980 nm NIR laser. The excited Yb 3+ ions undergo non‐radiative relaxation to ground state, and transfer energy via ET to surrounding Er 3+ ions.…”

“…For the UC emissions under a 980 nm laser excitation, the possible pathways are: ground state absorption (GSA), excited state absorption (ESA), energy transfer (ET), cross-relaxation (CR), and multi phonon relaxations (MPR) (Figure 4d). [9] The Yb . [26] Moreover, back energy transfer (BET) from excited Er 3 + ions to Yb 3 + , may also result in populating the green-emitting ( 2 H 11/2 / 4 S 3/2 ) and red-emitting ( 4 F 9/2 ) states of Er 3 + .…”

“…[9] Rare earth fluorides have relatively high photochemical stability and low phonon energies compared to other host materials such as oxides, phosphates, and vanadates. [2,[9][10]] YF 3 is a potential host lattice having low phonon energy, wide band gap (~10 eV), high UC efficiency, Y 3 + sites for favorable substitution of larger iso-valent Ln 3 + ions, shape and size-controlled synthesis, and attracted interest for various applications in solar cells, upconversion biolabel, color displays, and thermal sensing. [3,10a,11] Substitution of Th 4 + at suitable Y 3 + sites can be promising to enhance the UCL of Ln 3 + doped YF 3 upconversion phosphors as some lattice distortions will be generated via tetravalent ion doping at trivalent Y 3 + sites that may result in partially allowed electronic dipole f-f transitions of Ln 3 + ions.…”

“…The host lattice selection for the dispersion of activator/sensitizer pairs is crucial in the rational design of bright Ln 3+ ‐doped UC materials [9] . Rare earth fluorides have relatively high photochemical stability and low phonon energies compared to other host materials such as oxides, phosphates, and vanadates [2,9–10] .…”

“…The host lattice selection for the dispersion of activator/sensitizer pairs is crucial in the rational design of bright Ln 3+ ‐doped UC materials [9] . Rare earth fluorides have relatively high photochemical stability and low phonon energies compared to other host materials such as oxides, phosphates, and vanadates [2,9–10] . YF 3 is a potential host lattice having low phonon energy, wide band gap (~10 eV), high UC efficiency, Y 3+ sites for favorable substitution of larger iso‐valent Ln 3+ ions, shape and size‐controlled synthesis, and attracted interest for various applications in solar cells, upconversion biolabel, color displays, and thermal sensing [3,10a,11] .…”