Elsevier

Materials Research Bulletin

Volume 43, Issue 7, 1 July 2008, Pages 1716-1723
Materials Research Bulletin

Growth and characterization of metal ions and dyes doped KDP single crystals for laser applications

https://doi.org/10.1016/j.materresbull.2007.07.018Get rights and content

Abstract

The organic dyes (Amaranth, Rhodamine B and Methyl Orange) are doped in Potassium Dihydrogen Phosphate crystals. Influences of supersaturation and dye concentration in the solution, on the color and crystal habit of Potassium Dihydrogen Phosphate, were observed. Amaranth in the solution at low super saturation and high dye concentration colored the pyramidal section (1 0 1) of the crystals. The highly super saturated solutions produce entirely colored crystals. Dyes doped Potassium Dihydrogen Phosphate crystals were also grown by solution growth technique. The concentration of dopants in the mother solution was varied from 0.1 to 10 mol%. The studies on pure and doped Potassium Dihydrogen Phosphate crystals clearly indicate the effect of dopants on the crystal structure, in the absorption of IR frequencies and the non-linear optical property. The frequencies with their relative intensities are obtained in Fourier Transform-Infrared spectra of pure and doped Potassium Dihydrogen Phosphate. The very weak bands for dopants indicate its presence in low concentration. The absence of even such a weak band in the case of Potassium Dihydrogen Phosphate doped with Amaranth indicates the strong interaction with O–H groups. The calculated IR frequency 3333 cm−1 for O–H stretching was in close agreement with the experimentally obtained one for pure Potassium Dihydrogen Phosphate at 3340 cm−1.The doped crystals show good second harmonic generation efficiency. The dopants increase the hardness value of the material, which also depends on the concentration of the dopants. Dye doping improves the Nonlinear Optical properties of the grown crystals. Results of the growth kinetics of Potassium Dihydrogen Phosphate crystals in the presence of impurities are also discussed.

Introduction

One of the obvious requirements for a non-linear optical crystal is that it should have excellent optical quality. Potassium dihydrogen orthophosphate (KDP) is a model system for non-linear optical device application. Optical quality KDP (KH2PO4) crystals can be grown by conventional solution growth methods as well as by fast growth techniques. KDP is an efficient angle tuned dielectric medium for optical harmonic generation in and near the visible region. This material offers high transmission throughout the visible spectrum and meets the requirement for optical birefringence, large enough to bracket its refractive index for even extreme wavelength range over which it is transparent. Among non-linear optical phenomena, frequency mixing and electro-optic are important in the field of optical image storage and optical communication [1], [2], [3].

KDP finds widespread use as a frequency doubler in laser applications and has been studied in great detail. Improvement in the quality of the KDP crystals and the performance of KDP based devices can be realized with suitable dopants. To analyze the influence of metal ions and amino acid based dopants on the non-linear optical property of KDP crystals, efforts were made to dope KDP with dyes (Amaranth, Rhodamine B and Methyl Orange). The effects of impurity atoms on the quality and performance of the material are analyzed. In the present investigation, the growth aspects of KDP and doped KDP have been studied. Bulk crystals of KDP and doped KDP were grown by slow evaporation and also by slow cooling techniques. The structural, chemical, optical, mechanical and non-linear optical properties of the doped crystals were studied with the characterization studies such as powder XRD, FT-IR, UV–vis, micro hardness and SHG measurements, respectively. The results for doped KDP are compared with the results of the pure KDP crystals and as well as the results available in the literature.

Section snippets

Crystal growth

Pure KDP crystals were grown from aqueous solution by slow evaporation and also by slow cooling method (0.5 deg/day). The same method was followed for doped KDP crystals (0.1 mol% of Na2CO3 or AlPO4 or Amaranth or Rhodamine B or Methyl Orange). The solubility of doped KDP in the solvent was determined for each dopants for four different temperatures 30, 35, 40 and 45 °C by dissolving the KDP salt in deionized water in an air-tight container maintained at a constant temperature with continuous

Results and discussion

The dopants sodium and aluminium are expected to substitute for the potassium ions in the KDP lattice due to their valency as well as their similarity of ionic radius. However, the aluminium ions can occupy the interstitials instead of the potassium sites. The partial substitution of potassium ions may be explained as the consequence of the following chemical reactions.2KH2PO4 + Na2CO3  2Na+ + 2H2PO4 + 2K+ + CO32−KH2PO4 + (CH2)3C2N2H3(NH2)2COOH  (CH2)3C2N2H3(NH2)2CO-H2PO4 + KOHEarlier studies have reported

Conclusion

Optically clear Potassium Dihydrogen Phosphate and doped Potassium Dihydrogen Phosphate (Al, Na, Amaranth, Rhodamine B and Methyl Orange) crystals with dimension up to 25 mm × 22 mm × 10 mm have been grown by a slow evaporation technique and also by a slow cooling technique. Powder XRD was taken to analysis the structures of the doped crystals. In the Fourier Transform Infrared spectrum, the characteristic peaks due to C–O–H in plane and out of plane bands clearly demonstrate protonation of COO

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