Effect of hydrothermal time on the forming specific morphology of YPO4:Eu3+ nanoparticles for dedicated luminescent applications as optical markers

Eu-Doped YPO4 Luminescent Nanopowders for Anticounterfeiting Applications: Tuning Morphology and Optical Properties by a Rapid Microwave-Assisted Hydrothermal Method

“…No shift in the positions of the bands is observed between the samples. In general, the shape of the recorded bands does not differ from the spectra reported for Eu 3+ :YPO 4 obtained by the hydrothermal method without microwaves (Figure 8a, trace (A)) as well as those obtained by us 19 and other authors. 16,41,52,55,56 The asymmetry ratio R-factor (the ratio of the intensity of the emission transition associated with the electric dipole ( 5 D 0 → 7 F 2 ) to that associated with the magnetic dipole ( 5 D 0 → 7 F 1 )) was calculated to investigate the effect of MW on changes in the local environment of Eu 3+ ions.…”

“…It is likely that the MW-treated powders evolve directly from an amorphous system to the tetragonal crystalline phase of yttrium phosphate. 19 High crystallinity can also be observed at low treatment temperatures and times, as highlighted in Figure S2a,b of Supporting Information (SI). This is a significant aspect for phosphors since high crystallinity generally means fewer defects and stronger luminescence.…”

“…It should be noted that a similar value was obtained when nanoparticles of the same chemical composition were synthesized after 18 h of hydrothermal synthesis. 19 This shows that the efficiency and effectiveness of using MW in the synthesis process are definitely higher. In addition, when comparing the sample without MW processing (labeled No MW in Figure 8c), it is worth noting the shape of the bands.…”

“…For comparison, the spectrum of the sample obtained after 12 h by the classical hydrothermal method using conventional heating at 200 °C is also shown (red line (B)). 19 The spectra of all prepared powders are reported in Figure S5 of the SI file.…”

“…54 At the same time, the luminescence centers associated with the presence of dopant ions close to the surface of the nanoparticle will also have different properties than those in the volume of the nanoparticle, being more sensitive to changes in its environment, making rod-like morphology suitable for specific applications such as optical markers. Well-crystallized Eu 3+ :YPO 4 nanorods were obtained by conventional hydrothermal process only after prolonged thermal treatments at 200 °C (for 12−18 h), 19,23 while Vanetsev et al observed a similar morphology in hydrate YPO 4 •0.8H 2 O nanopowders obtained after 2 h of MW-assisted thermal treatment. 4 In our case, this morphology was obtained at much lower treatment times with considerable time and energy savings.…”