Regulating Mid-infrared to Visible Fluorescence in Monodispersed Er3+-doped La2O2S (La2O2SO4) Nanocrystals by Phase Modulation

Abstract

Rare earth doped mid-infrared (MIR) fluorescent sources have been widely investigated due to their various potential applications in the fields of communication, chemical detecting, medical surgery and so forth. However, with emission wavelength extended to MIR, multiphonon relaxation process that strongly quenched the MIR emission is one of the greatest challenges for such practical applications. In our design, we have described a controllable gas-aided annealing strategy to modulate the phase, crystal size, morphology and fluorescent performance of a material simultaneously. Uniform and monodispersed Er3+-doped La2O2S and La2O2SO4 nanocrystals with a similar lattice structure, crystallinity, diameter and morphology have been introduced to investigate the impact of multiphonon relaxation on luminescence performance. Detailed spectroscopic evolutions in the region of MIR, near-infrared (NIR), visible upconversion (UC) and their corresponding decay times provide insight investigation into the fluorescent mechanism caused by multiphonon relaxation. A possible energy transfer model has also been established. Our results present direct observation and mechanistic investigation of fluorescent evolution in multiphonon relaxation process, which is conductive to design MIR fluorescent materials in the future. To the best of our knowledge, it is the first investigation on MIR fluorescent performance of La2O2S nanocrystals, which may find various applications in many photoelectronic fields.

Morphological evolution of upconversion nanoparticles and their biomedical signal generation

“…The morphology transformation may occur due to the high pressure induced by the solution phase on the solid-solution phase inside the reaction vessel at HR times beyond this threshold. After the threshold HR time, the particles may be unable to withstand the high pressure and may tend to diffuse into other particles 29 , 30 , resulting in the formation of both spherical and irregularly shaped UCNPs due to the insufficient surface energy to form the new nanoparticles 31 – 33 . When the HR time is further increased, i.e., at 24 h, mainly large agglomerated particles were obtained.…”

Weakening thermal quenching to enhance luminescence of Er3+ doped β‐NaYF4 nanocrystals via acid‐treatment

“…Furthermore, the fluorescence decay time of the 4 S 3/2 , 4 F 9/2 , 4 I 13/2, and 4 I 11/2 states of Er 3+ in β ‐NaYF 4 and β ‐NaYF 4 ‐HCl NCs were measured, depicted in Figure D‐G. After acid‐treatment, the emerging defects would more and less quench the fluorescence emission of Er 3+ in all bands via multiphonon relaxation, which is a rapid process, and can shorten the lifetime of an intermediate level . Hence, Er 3+ has shorter UC, NIR and MIR fluorescence lifetime in β ‐NaYF 4 ‐HCl NCs.…”

Polymer-Functionalized Upconversion Nanoparticles for Light/Imaging-Guided Drug Delivery

“…However, after 8 h, the obtained UCNPs exhibited spherical and irregular shapes, and then large and irregularly shaped UCNPs were harvested after 15 h, 43 which are likely the result of the instability of the system under high pressure at long reaction times. 44,45 This technique can, however, be used to adjust the size by changing the dopant concentration, which furthermore alters the UCNPs hexagonal phase, yielding enhanced visible luminescence intensity under 980 nm diode laser excitation. 46 It is not only the dopant concentration that can change emission colors and intensity, but also the experimental conditions employed during the synthesis.…”