Heterogeneous Oxysulfide@Fluoride Core/Shell Nanocrystals for Upconversion-Based Nanothermometry

Abstract

Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs) often suffer from weak luminescence, especially when their sizes are ultrasmall (less than 10 nm). Enhancing the upconversion luminescence (UCL) efficiency of ultrasmall UCNPs has remained a challenge that must be undertaken if any practical applications are to be envisaged. Herein, we present a Ln3+-doped oxysulfide@fluoride core/shell heterostructure which shows efficient UCL properties under 980 nm excitation and good stability in solution. Through epitaxial heterogeneous growth, a ∼4 nm optically inert β-NaYF4 shell was coated onto ∼5 nm ultrasmall Gd2O2S:20%Yb,1%Tm. These Gd2O2S:20%Yb,1%Tm@NaYF4 core/shell UCNPs exhibit a more than 800-fold increase in UCL intensity compared to the unprotected core, a 180-fold increase in luminescence decay time of the 3H4 → 3H6 Tm3+ transition from 5 to 900 μs, and an upconversion quantum yield (UCQY) of 0.76% at an excitation power density of 155 W/cm2. Likewise, Gd2O2S:20%Yb,2%Er@NaYF4 core/shell UCNPs show a nearly 5000-fold increase of their UCL intensity compared to the Gd2O2S:20%Yb,2%Er core and a maximum UCQY of 0.61%. In the Yb/Er core–shell UCNP system, the observed variation of luminescence intensity ratio seems to originate from a change in lattice strain as the temperature is elevated. For nanothermometry applications, the thermal sensitivities based on thermally coupled levels are estimated for both Yb/Tm and Yb/Er doped Gd2O2S@NaYF4 core/shell UCNPs.

Robust Strategy to Improve the Compatibility between Incorporated Upconversion Nanoparticles and the Bulk Transparent Polymer Matrix

“…The small peak at 1064 cm −1 is assigned to the syndiotactic peak of PMMA. In addition, the successful grafting of PMMA onto the surface of UCNPs−Br nanoparticles by photoinduced metal-free SI-ATRP was further demonstrated by 1 H NMR in CDCl 3 , as shown in Figure S8. These results indicate that the PMMA chain had been crafted by photoinduced metal-free SI-ATRP on the surface of the UCNP.…”

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

“…However, temperature measurement in scientific research and industrial production always confronts high-pressure environments, strong corrosiveness, nanoscale confined environments, and heavy electromagnetic interference. Therefore, exploring novel temperature-sensing devices with particular characteristics has become a research focus. − Recently, the focus on optical pyrometry has escalated, as it can take advantage of temperature-dependent spectral parameters such as fluorescence intensity ratios (FIRs) to monitor temperature, producing highly sensitive and fast response characteristics, exploiting the different responses of the emission intensity that arise from the two thermal coupling levels (TCLs) or nonthermal coupling levels (NTCLs) of rare earth (RE) ions to temperature. − …”

“…The precursor was heated with sulfur powder and Na 2 CO 3 in a muffle furnace at 900 °C for 5 h and then washed with dilute hydrochloric acid; finally, La 2 O 2 S doped with Er 3+ /Yb 3+ was obtained. The LOS-EY NCs could be described as (La 1−x−y Er x Yb y ) 2 O 2 S, where x = 0.01m, y = 0.01n, and (m, n) = (1, 0), (2, 0), (3, 0), (2,4), and (3,6); for a more accurate representation, the corresponding samples were labeled as LOS-E 1 , LOS-E 2 , LOS-E 3 , LOS-E 2 Y 4 , and LOS-E 3 Y 6 .…”

NIR-Driven White Light Diode Formed with UCNP@AIEgen Nanocomposites

“…4,5 Studies of lanthanide-doped materials have identified a foundation for development in the field of upconversion nanoparticles (UCNPs). The characteristics of UCNPs have been used in nanothermometry and temperature sensing, 6,7 the determination of the phytohormone salicylic acid in plant extracts, 8 and mercury ion sensing in green tea, 9 Most WLEDs are manufactured using luminescent downshifting phosphors combined with UV, violet, or blue lightemitting diode (LED) chips. The adoption of UCNPs and infrared LED chips in the manufacture of WLEDs would offer a new strategy based on upconversion materials rather than traditional downconversion materials.…”

“…White light-emitting diodes (WLEDs) have attracted considerable attention in solid-state lighting because of their high luminous efficiency, energy-saving capacity, ecofriendliness, and long-term stability. − Upconversion materials can convert the excitation of near-infrared (NIR) light to the emission of visible or ultraviolet (UV) light through multiphoton step-by-step absorption. , Studies of lanthanide-doped materials have identified a foundation for development in the field of upconversion nanoparticles (UCNPs). The characteristics of UCNPs have been used in nanothermometry and temperature sensing, , the determination of the phytohormone salicylic acid in plant extracts, and mercury ion sensing in green tea,…”