Morphological and optical properties of doped potassium hydrogen phthalate crystals
Introduction
Potassium hydrogen phthalate or potassium acid phthalate (KAP) with the chemical unit formula K(C6H4COOH-COO) is a semiorganic salt that belongs to the alkali acid phthalate series, has an orthorhombic symmetry with the space group Pca21 [1] and shows a perfect cleavage along (0 1 0) plane. The KAP crystal presents long-term stability and is used in devices due to its electro-optical properties [2]. It also exhibits interesting piezoelectric, pyroelectric and elastic properties that are useful in many applications [3], [4]. Moreover, KAP crystals play an important role in the field of non-linear optics and are used in quantitative X-ray analysis [5]. Recently, KAP crystals were used as substrate for epitaxial growth of oriented polymers [6], [7] and for hierarchical growth of organized materials [8].
Numerous authors report the relation between growth conditions and morphology for pure [9], [10], [11] and doped [12], [13], [14] KAP crystals. Theoretical studies were dedicated to the growth kinetics from aqueous solutions [15]. Recently new growth techniques were developed [16].
The properties of KAP crystals doped with different impurities were extensively studied [17], [18], [19], [20]. Recent reports focus on luminescence and up conversion due to second harmonic generator properties of the host KAP crystals doped with different dyes with potential applications as solid state tuneable lasing media [21], [22], [23], [24].
Studies regarding tunable solid-state lasing materials are aimed on dye-doped polymers, clays or liquid crystals. An easily growing non-linear optical (NLO) single-crystalline material that combines the qualities of liquid dye-lasers such as high efficiency and broadband tuneability with the flexibility and the convenience in operation offered by solid state lasing media represents an interesting alternative. The aim of this paper is to present such a material in the form of rhodamine 6G (Rh 6G) doped KAP crystal with the preserved optical quality and the improved emission properties induced by the polyvinylpyrrolidone (PVP) doping.
This report presents a set of studies regarding the influence of doping with rhodamine 6G and polyvinylpyrrolidone on the structural, morphological and optical properties of potassium hydrogen phthalate crystals. The results obtained from the single-crystal and powder X-ray diffraction, optical transmission and photoluminescence measurements are presented.
Section snippets
Experimental
Pure and doped crystals were grown by the evaporation technique from aqueous solutions prepared using deionized water (Millipore Ultra-Q, 18.2 M Ω cm@25 °C resistivity) and A.C.S. grade (meets the specifications of the American Chemical Society) potassium hydrogen phthalate (C8H5O4K) supplied by Aldrich. Rhodamine 6G Basic Red 1 of 99% purity (Aldrich) and polyvinylpyrrolidone (C6H9NO)n of 1:300,000 MW (Aldrich) were used as dopants without further purification and KAP, PVP doped KAP (PKAP), Rh 6G
Results and discussion
Pure and doped as-grown KAP crystals are presented in Fig. 1. The PVP doping of the KAP crystals leads to a change of the morphology as it can be observed in Fig. 1a–c. PVP is an additive used in experimental studies because of its preferential pattern of binding on growth directions [26]. According to the schematic non-equivalent growth directions of KAP [27], the addition of PVP inhibits the advancement rate of the four faces of the {1 1 0} form thus promoting growth on the faces of the {1 1 1}
Conclusions
Good quality single-crystals of pure and doped KAP (KAP, RKAP, PKAP and RPKAP) were grown by solution evaporation technique. Addition of polyvinylpirrolidone (PVP) to the KAP crystals changes the morphology from pseudo-hexagonal shape to rhomb shaped crystals by promoting the advancement rate on the faces of the {1 1 1} form but does not affect the structure of the single PKAP or PRKAP crystals.
Besides the peaks indexed with Powder Diffraction File (PDF) database of International Centre of
Acknowledgement
The author gratefully acknowledges the financial support of the Romanian Ministry of Education and Research (Contract PN09-450102) and UEFISCU-CNCSIS (Project IDEI code 344/2007).
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2017, Journal of Crystal GrowthCitation Excerpt :Potassium acid phthalate (KAP) is a semiorganic compound and crystallizes in orthorhombic system with the space group of pca21 and its lattice parameters are a=9.605 Å, b=13.331 Å, c=6.473 Å and α=β=γ=90° [1,2].