Access Type

Open Access Embargo

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Federico A. Rabuffetti

Abstract

The major scientific problems that associated with the state-of-the-art upconverting nanocrystal system (rare-earth-doped β-NaYF4) are lower quantum efficiency, lack of full-spectrum color tunability, and difficulty in achieving single-band red emission. The major scientific strategies that employed to address these scientific problems are based on nanostructuring, tuning rare-earth concentration, and tuning host chemical composition. The reported articles during the past few decades clearly illustrated that nanostructuring and tuning rare-earth concentration hadn’t bought considerable contribution to synthesize efficient and color-tunable upconverting nanocrystal systems. However, the ability to tune the chemical composition of the host to design efficient and color-tunable upconverting nanocrystal system was limited due to the fixed crystal structure of β-NaYF4 host. Therefore, there is a crucial need to come up with a chemically and structurally flexible host matrix. Searching literature, alkaline-earth-fluorohalides (MFX) were identified as a suitable chemical platform to study this research approach.

Size- and shape-controlled Er:Yb:SrFCl and Er:Yb:SrFBr upconverting nanocrystal systems were synthesized using two novel colloidal synthetic routes: one-step thermolysis and two-step thermolysis. The optimized reaction variables (reaction temperature, reaction time, precursor concentration, and the solvent system) for these systems were identified by using the trial method. However, after numerous trials Er:Yb:SrFCl nanocrystals were obtained at two different temperatures 225 and 250 with mean diameters of 12.1–17.8 and 13.0–16.7 nm, respectively. Similarly, Er:Yb:SrFBr nanocrystals were synthesized at two different temperatures 225 and 250 with mean diameters 41.7–52.0 and 45.6–55.3 nm, respectively. Results from chemical, morphological, and luminescence techniques of as-prepared nanoparticles were characterized as a function rare-earth concentration, synthesized temperature, and host chemical composition. Also, the structural characterizations were analyzed only as a function of the host’s chemical composition.

Next, the third novel synthetic route was developed to produce Er:Yb:BaFCl nanocrystals. For this synthesis decomposition if metal chlorodifluoroacetates (dual halogen source) by hot-injection route was employed. After performing numerous reaction trials, spherical shaped nanocrystals with a mean diameter of 18.721.5 nm range was obtained. Similar characterization techniques used for Er:Yb:SrFX (X = Cl and Br) systems were used to analyze the effect of rare-earth concentration on the structural and luminescence properties of these materials.

Finally, this Thesis demonstrates the ability of rare-earth-doped alkaline-earth fluorohalides to work as optical temperature sensors.

Results presented in this Thesis demonstrate that by identifying the effect of the chemical composition of host on the structural and luminescence properties contribute to design efficient and color-tunable nanocrystals.

Available for download on Wednesday, January 12, 2022

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