Dyeing KDP

Janardhanan Anand Subramony, Purdue University

Abstract

Studies comprising the crystal growth and characterization of KH 2PO4(KDP) containing organic molecules particularly sulfonated dyes are described. KDP is shown to, orient a variety of anionic molecules on the {101} growth sectors due to electrostatic interactions between the molecules and the crystal surface. The spectroscopic properties of the dyed KDP crystals are presented that indicate a perturbation in the electronic energy levels of the dyes in the crystal. The sulfonated dyes are also shown to selectively recognize the various dislocation hillocks on the pyramidal {101} faces of KDP during growth from aqueous solution. KDP grown in the presence of fluorophores, coumarins and stilbene provided fluorescent crystals. The coumarins in KDP also showed phosphorescence. The fluorescence lifetime of one of the coumarins in the crystal showed sharp changes at the ferroelectric phase transition temperature of KDP. For stilbene, results on fluorescence depolarization, anisotropy in the excitation and emission, and an orientation in the KDP lattice are provided. The study of the effect of dyes on the structural phase transitions of KDP led to the reinvestigation of the high temperature phase behavior of pure KDP. The tetragonal phase of KDP undergoes two ill-defined high temperature transitions that have eluded characterization for more than 30 years as the crystal shatter on heating. We carried out a reexamination of the progression of these transformations using hot stage optical polarization microscopy and x-ray diffraction. This study demonstrated that the progress of the high temperature transformations in KDP is strikingly heterogeneous with phase transitions and dehydration taking place concomitantly at different sites in the same crystal, evidenced by the appearance of crystalline and polycrystalline islands upon heating. Single crystal x-ray diffraction was performed on the crystalline domains, which provided three new crystal structures for KDP. The progression of changes were also probed using micro-Raman spectroscopy whereby we de-convoluted the signals of the polycrystalline and crystalline domains. The results indicated that the pyro- and metaphosphate dehydration products, which are formed upon heating KDP are localized in the polycrystalline material.

Degree

Ph.D.

Advisors

Kahr, Purdue University.

Subject Area

Chemistry|Materials science|Condensation

COinS