Super Bright Red Upconversion in NaErF₄:0.5%Tm@NaYF₄:20%Yb Nanoparticles for Anti-counterfeit and Bioimaging Applications

Abstract

Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600−900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF 4 :0.5%Tm@ NaYF 4 :20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF 4 :0.5%Tm@NaYF 4 (core@inactive shell). Here, an Er 3+ -enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er 3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm 3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb 3+ ions efficiently transfers the energy to the Er 3+ -enriched core, which suppresses the nonradiative channel rate, and Tm 3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.

Brilliant Nonlinear Optical Response of Ho3+ and Yb3+ Activated YVO4 Nanophosphor and Its Conjugation with Fe3O4 for Smart Anticounterfeit and Hyperthermia Applications

“…There are reports on the use of nanoparticles for anticounterfeiting applications . Most of the reported anticounterfeiting applications are based on UV light excitation. , However, reports on NIR light excitation based anticounterfeiting applications are very less due to small-sized spots of the laser (1–2 mm in diameter) that it cannot cover larger areas (a few cm in any dimensions), which can be done easily by UV light. , In this work, we overcome this problem using a proper collimator as well as a suitable filter. For its implication, a demonstration has been carried out by dispersing the YVO 4 :Ho 3+ /Yb 3+ nanophosphor into methanol and dispersed particles are used to write letters or numerals over a sheet of paper (shown in Figure ).…”

X-ray triggered pea-shaped LuAG:Mn/Ca nano-scintillators and their applications for photodynamic therapy

“…Among these, lanthanide rare earth materials have been widely studied in the field of RT and PDT due to their high atomic number and unique 4f electronic layer structure. [28][29][30][31][32] For instance, Li et al designed and synthesized Gd 2 (WO 4 ) 3 :Tb@MC540 with excellent green light emission using a hydrothermal method. 33 Under the action of X-rays, the Gd 2 (WO 4 ) 3 :Tb scintillation with X-ray antennae and ability to transfer energy activated MC540 to initiate X-PDT under multimodal CT/MRI imaging, which exhibits a good tumor growth inhibition rate of 75%.…”

Enrichment of Crystal Field Modification via Incorporation of Alkali K+ Ions in YVO4:Ho3+/Yb3+ Nanophosphor and Its Hybrid with Superparamagnetic Iron Oxide Nanoparticles for Optical, Advanced Anticounterfeiting, Uranyl Detection, and Hyperthermia Applications

“…However, UV light is hazardous for the surrounding environment including the persons who are working. The number of literature studies using NIR light excitation is very less because of many limitations such as a very small spot size of the laser (1–2 mm diameter) and need of a proper collimator and proper filters. − However, if the above limitations are overcome, it has many advantages over UV light excitation because of deep penetration of the NIR light and thus materials having a few cm thickness can be detected.…”