Growth of KDP: Fe3+ Crystals from Oversaturated Aqueous Solutions

Vera Manomenova,Elena Rudneva,Alexey Voloshin,Svetlana Baskakova

doi:10.3390/cryst9120646

Abstract

The KH2PO4 solubility curves in pure water and in water with the addition of 50 ppm Fe3+ were refined. The KH2PO4 and KH2PO4: Fe3+ solutions stability to supercooling was evaluated by polythermal studies of the width of metastable zone. It was shown that Fe3+ addition makes the solution more stable. A series of Fe3+ doped KDP crystals were grown at different temperature and hydrodynamic regimes at supersaturation level up to 0.45. Their real structure was studied by X-ray projection topography and, as a result, the most suitable growth conditions are chosen. The transmittance spectra of prism sectors with ferric iron concentrations CFe up to 102 ppm were obtained. It was found that KDP crystals with CFe >60 ppm can be used as optical filters for suppressing transmission in UV-C and UV-B ranges.

Highlights

The potassium dihydrogen phosphate (KH2 PO4 ) crystal (KDP) is widely used in non-linear optics and laser technology for the manufacture of optical modulators, Q-switches, and laser frequency converters [1,2,3,4,5,6]
Studies of atomic structure of KDP crystal faces have explained this phenomenon: it was found that the prism surface is electrically neutral since it is formed by both potassium cations
The dependence of the growth steps velocity on the solution supersaturation for the prism sector of the KDP crystal could be characterized by the existence of so-called "dead zone" σ < σd and the critical supersaturation σ*

Summary

Introduction

The potassium dihydrogen phosphate (KH2 PO4 ) crystal (KDP) is widely used in non-linear optics and laser technology for the manufacture of optical modulators, Q-switches, and laser frequency converters [1,2,3,4,5,6]. These crystals have high resistance to laser radiation and are not subject to various induced effects. Adsorbed M3+ ions, which are one of the main accompanying impurities for KDP crystal, form fixed blockers (so-called Cabrera–Vermilyea fence) and brake movement of the growth steps on the {100}-faces [11]. The analysis of the kinetic curves obtained for solutions with Fe3+ concentrations (CFe ) up to 7 ppm showed that, at a low impurity, concentration the supersaturation threshold values (σd and σ*) increase linearly with the

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