Keywords

Upconversion Nanoparticles (UCNPs, ) NaYF₄:Yb³⁺, Er³⁺, Environmental Stability, Photoluminescence Spectroscopy, Cerium Doping

Abstract

Upconversion nanoparticles (UCNPs), particularly those based on Sodium Ytterium Floride ( NaYF₄) doped with Lanthanide ions, have emerged as promising multifunctional materials owing to their exceptional capacity to convert near-infrared (NIR) light into visible or ultraviolet light through multiphoton excitation processes. Their remarkable resistance to photobleaching, minimal toxicity, and customizable emission characteristics render them ideal candidates for applications in both environmental monitoring and biomedical fields. This thesis investigates the synthesis, structural characterization, and functional performance of NaYF₄:Yb³⁺,Er³⁺ upconversion nanoparticles s, with a focus on its applicability in fog. In response to the limitations of conventional fog detection technologies under low-visibility conditions, these UCNPs were explored for their NIR-to-visible emission capability under 980 nm excitation offering compatibility with night-mode surveillance systems for real-time environmental monitoring.

To evaluate their durability in real-world settings, a comprehensive stability assessment was conducted. The nanoparticles were subjected to environmental conditions including elevated temperatures (400–800 °C), high humidity, ultraviolet irradiation, simulated sunlight, and prolonged white LED exposure. Structural and optical changes were characterized through X-ray diffraction (XRD), SEM imaging, and PL spectroscopy techniques. Results revealed that exposure to harsh conditions, particularly humidity and thermal stress induced phase transitions that harsh environmental conditions, especially moisture and heat, triggered phase transitions arising from luminescent hexagonal β-phase to the less emissive cubic α-phase, accompanied by defect generation and surface quenching effects, ultimately diminishing upconversion efficiency."

luminescent hexagonal β-phrase to the less efficient cubic α-phase, along with defect formation and surface quenching, leading to reduced upconversion performance.

To enhance luminescent efficiency and environmental stability, the study also introduced cerium (Ce³⁺) as a co-dopant. Cerium incorporation was found to modulate the local crystal field, suppress non-radiative relaxation pathways, and optimize energy transfer between Ytterbium ( Yb³⁺) , Erbium (Er³⁺) ions. Three distinct cerium-doping strategies were systematically explored to assess their influence on emission behavior, structural integrity, and photostability under aging conditions.

Overall, this work highlights the potential of engineered NaYF₄:Yb³⁺,Er³⁺ UCNPs for advanced applications in smart transportation systems. The findings contribute valuable insights into the design of robust, efficient, and environmentally resilient upconversion nanomaterials for next generation sensing and technologies.

Completion Date

2025

Semester

Spring

Committee Chair

Sudipta, Seal

Degree

Master of Science in Materials Science and Engineering (M.S.M.S.E.)

College

College of Engineering and Computer Science

Department

material science and engeneering

Identifier

DP0029325

Document Type

Dissertation/Thesis

Campus Location

Orlando (Main) Campus

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