Potassium Dihydrogen Phosphate Single Crystals Research Articles

Properties of nonlinear optical absorption and refraction of rapidly grown KDP crystals

Potassium dihydrogen phosphate (KDP) single crystals grown under different conditions were obtained by the “point seed” technique. Third-order nonlinear optical properties of type-II samples which were prepared from the pyramidal and prismatic sections of crystal, respectively, were systematically investigated using the Z-scan technique at λ = 532 nm. Some heat-treated samples have been studied simultaneously. The results show that the nonlinear optical absorption and nonlinear optical refraction have been reflected, meanwhile, the nonlinear refractive index (n2) is positive, suggesting the generation of self-focusing effect. Furthermore, the results indicate that the nonlinear absorption and nonlinear refraction were associated with the growth conditions of the crystal. The prismatic sample grown under the relatively low growth temperature range (45∼25 °C) and small supersaturation (4 %) possessed a smaller nonlinear absorption coefficient (β) and n2 (β=4.73 × 10−13 m/W, n2=2.82 × 10−13 esu) than that of the others. In addition, the values of nonlinear absorption and nonlinear refraction of the samples can be further reduced after thermal annealing. These results may provide an assist to understand the mechanism of laser-induced damage of KDP crystals.

Spontaneous formation of a periodically striped structure in a gel-incorporated KDP single crystal

Typically, single crystals grown from hydrogels uniformly incorporate the gel-networks inside. However, in this study, we discovered a periodically striped microstructure in potassium dihydrogen phosphate (KDP) single crystals cultivated from silica hydrogels. This was the result of spontaneously non-uniform gel-incorporation, as demonstrated by time-of-flight secondary ion mass spectrometry. Furthermore, despite the non-uniformly distributed gel networks inside the crystal, its single-crystallinity remained intact, as verified by X-ray diffraction. Our hypothesis for the incorporation mechanism is that partial gel incorporation at certain rates of crystal growth periodically changes the local gel strength surrounding the growing crystal, leading to spontaneous alternations in the concentration of incorporated gel-networks.

Doped potassium dihydrogen phosphate single crystals with enhanced second-harmonic generation efficiency: an investigation of phase purity, nonlinear, piezoelectric, optical, and crystalline qualities

We investigated the impact of itaconic acid (ITA) on potassium dihydrogen phosphate (KDP) aimed at concentrations of 1, 3, and 5 mol % on Single Crystal x-ray Diffraction, Fourier Transform Infra-Red, absorption of optical charm, Powder XRD, improved second Harmonic Generation competency, and third order non-Linearity of fully grown solitary crystals formed by slow cooling (Low Temperature Solution Growth). The crystals were crushed into a powder with micron-sized crystals for x-ray diffraction research. The Powder XRD spectrum of different ITA doped KDP concentrations showed fewer peaks with higher intensities than pure KDP crystals. Doping in the KDP crystal matrix accelerate growth in the [200] plane. Despite vibration assignment modes of ITA doped KDP, the FT-IR spectrum shows doping materials in KDP crystalline media. ITA doped KDP showed 90% optical transmission in UV–vis-NIR spectroscopy, whereas pure KDP possessed 60%. The dielectric investigation found that doped KDP crystals had lower dielectric loss and greater dielectric constants than pure counterparts. In pure and doped crystals, piezoelectric effects and second harmonics are premeditated. Using the Z scan approach, we were able to assess the third order nonlinear optical behaviour of pure crystal samples as well as the effects of self-defocusing caused by doping of ITA in KDP. ITA doping contributes to the growth, nucleation, and induction period. Doping concentration initially accelerated growth. Photoluminescence study shows that fully formed crystals have fewer defects. High Resolution XRD study determined crystal quality.

The effect of magnesium chloride doping on structural, thermal, optical, nonlinear optical and electrical properties of Potassium Dihydrogen Phosphate single crystal

The effect of magnesium chloride doping on structural, thermal, optical, nonlinear optical and electrical properties of Potassium Dihydrogen Phosphate single crystal

Enhanced 532 nm laser damage threshold and optical performance of KDP crystals by Zn2+ doping

Potassium dihydrogen phosphate (KDP) single crystals doped with a series of trace Zn2+ were prepared by “point seed” technique. The content of Zn of KDP crystal was detected using inductively coupled plasma-optical emission spectrometer (ICP-OES). Small differences were found in Zn content of pyramidal and prismatic samples. The ultraviolet–visible (UV–vis) spectra show that the transmitting percentage of doped KDP crystals increases with trace Zn2+ while the transmittance of crystal samples with excessive Zn2+ reduces in UV region. The structural analysis has been performed using infrared spectroscopy (IR). The results illustrate that the crystal network becomes compact after heat treatment or with low concentration doping. The photoluminescence (PL) spectra analysis indicates that the concentration of micro defects of all doped pyramidal samples is lower than that of un-doped samples as well as doped prismatic samples. After thermal annealing, the intensity of PL spectrum of doped sample decreases not obvious compared to un-doped samples. The laser-induced damage threshold (LIDT) results show that the un-doped prismatic sample has relative the lowest LIDT of 3.59 J/cm2 under the condition of 1-on-1. The LIDT of prismatic sample doped with 1000 ppm Zn2+ reaches 13.88 J/cm2 in the test mode of R-on-1 after heat treatment, which mainly is attributed to the relatively low concentration of micro defects.

Probing the stochastic behavior of the onset of plasticity for potassium dihydrogen phosphate single crystal by grating spherical nanoindentation

To support high-throughput instrumental nanoindentation testing, the statistical dataset of incipient plasticity via first pop-in event was acquired in potassium dihydrogen phosphate (KDP) single crystal. The onset of plastic deformation occurred stochastically over a wide range of critical stresses. The corresponding maximum shear stress below the indenter could approach the theoretical shear stress for the activating of a single dislocation. The result of the experiment shows that the threshold stress for the onset of plasticity could be well represented by the Gaussian distribution law and its average value obviously depends on the crystal orientation. Moreover, the activation volume of dislocation nucleation was experimentally characterized on the length scale of the atomic vacancy (28 ± 3.5 Å3) and independent of the crystalline orientation. This suggests that the point defects caused by breakage of the atomic bond on the cleavage surface are the activation source for the dislocation nucleation.

Effect of some hydroxyl additives on the growth and optical properties of KDP crystals

Potassium dihydrogen phosphate (KDP) single crystal was doped with disodium tetraborate decahydrate (or borax), L-alanine, and disodium ethylenediaminetetraacetate (or disodium EDTA) with 0.05 mol%, 9 mol%, and 2 mol% concentration in the aqueous solution, respectively. These crystals were fabricated by the temperature reduction method incorporating the Sankaranarayanan-Ramasamy technique and were grown onto seed crystals that were inclined at the type I phase-matching angle to the vertical. Each doped KDP single crystal rod was cut into three parts: the bottom, the middle, and the top, which were related to the fabrication temperature range of 50–40 °C, 40–30 °C, and 30–20 °C, respectively. The effect of the additives on the growth and optical properties of KDP crystals was evaluated through Ultraviolet–Visible spectroscopy, Raman spectroscopy, X-Ray Diffraction analysis, Energy-Dispersive X-ray spectroscopy, and Second Harmonic Generation measurement. The hydroxyl impurities have improved the optical properties of KDP crystals by contributing more hydrogen bonds to the KDP lattice. The doped KDP crystals increased SHG efficiency by 1.19 to 2.36 times compared with pure KDP crystals.

532 nm laser damage and nonlinear absorption of Cr2O72− doped KDP crystals

Potassium dihydrogen phosphate (KDP) single crystals doped with a series of trace dichromate (Cr2O72−) were prepared using “point seed” technique. The IR spectra suggest that the KDP crystal network becomes compact with trace of Cr2O72− while the lattice of crystal also can be destroyed by excessive doping. The UV–Vis spectra show that the transmittance percentage is descended of the doped KDP crystals. Z-scan analysis demonstrates that with increasing of Cr2O72− concentration, a gradual raise has been observed for the nonlinear absorption coefficient (β). The laser-induced damage threshold (LIDT) at 532 nm of the KDP crystal doped with 3000 ppm Cr2O72− is found to be 28.29 J/cm2 which is higher than that of pure one under the R-on-1 model. However, as the doping concentration continues to increase, the LIDT decreases significantly. The variation of photoluminescence (PL) results is also consisted with the trend of LIDT for the doped samples. The LIDT of pyramidal sample is higher than that of prismatic one with the same doping concentration. The results suggest that the laser damage of doped crystal may be due to a synergistic effect of the concentration of micro defects and nonlinear absorption.

In situ growth of an ethyl p-hydroxybenzoate single crystal by the vertical Bridgman technique: a potential nonlinear optical material for third-harmonic generation

Optically transparent single crystals of ethyl p-hydroxybenzoate (EPHB) were successfully grown by the vertical Bridgman technique. The crystalline phase and unit-cell dimensions were obtained from powder X-ray diffraction using Rietveld analysis. The presence of defects and grain boundaries was investigated by high-resolution X-ray diffraction. The optical quality of the grown single crystal was assessed by UV–Vis and photoluminescent spectroscopies. A blue emission, with a bi-exponential decay time, was obtained from time-resolved photoluminescence upon laser excitation at 266 nm. The mechanical strength of the EPHB single crystal was studied by Vickers hardness testing. A decrease in the laser-damage threshold was observed with a nanosecond Nd:YAG laser source for increased pulse repetition rates. The third-order nonlinearity, nonlinear absorption coefficient and nonlinear refractive index were measured using the Z-scan technique with a femtosecond Ti:sapphire laser. The third-order nonlinear coefficient values for the grown crystal were compared with those of a potassium dihydrogen phosphate single crystal.

Polarimetric studies of L-arginine-doped potassium dihydrogen phosphate single crystals

Conoscopic interference patterns, channelled spectra and polarimetric techniques have been used for the characterization of pure and doped (with L-arginine amino acid) potassium dihydrogen phosphate (KDP) single crystals. Experimental polarimetric data have been obtained for the frequently used wavelength of 633 nm and for two close wavelengths of 532 and 543 nm in a high-accuracy dual-wavelength polarimeter. The measurement of eigenwave ellipticity in the [100] and [010] directions and between 295 and 340 K shows small differences in the absolute values of the specific optical rotations of KDP crystals doped with L-arginine in the range of 0.7–3.8 wt%. It is found that the gyration tensor component g 11, specific optical rotation and eigenwave ellipticity show different dispersion in the visible spectral region.

Optical and thermal properties of l-tartaric doped KDP crystals

The impact of l-tartaric acid (LTA) doping on different properties of potassium dihydrogen phosphate single crystals grown by point seed rapid growth technique has been obtained. Powder X-ray diffraction (PXRD) analysis was completed to prove that the l-tartaric adding had no prominent effect on the unit cell parameters. The existence of various functional groups were identified by FT-IR spectroscopy. Optical transmittance of the grown crystal has been studied by UV–Vis-NIR spectral analysis, indicating that the transmittance of crystals increased with the addition of l-tartaric, and the optical transmittance reached an optimum value at 1mol% doping concentration. Thermal stability measurement was carried out by TG-DTA study. This paper also analyzed the band gap and refractive index of l-tartaric acid doped KDP, and the physicochemical mechanism of adding on the effect of optical properties of KDP crystal was also discussed.

Investigation on the impact of xylenol orange dye on the growth and properties of unidirectional grown KDP crystals for photonic applications

Unidirectional (1 0 1) bulk size xylenol orange dye-doped potassium dihydrogen phosphate single crystals were grown by Vacuum Assisted Sankaranarayanan-Ramasamy method so as to improve the properties of the crystal. The objective is to study the impact of organic dyes on properties of the crystal and understand how it could be used for relevant applications. Optical transmission decreases and thermal properties remain the same for the dye-doped crystals whereas the addition of dye improves mechanical, dielectric and photoconduction properties. On comparison, a stronger absorption is identified at 480 nm for the dye-doped crystal. Laser damage threshold confirms that 0.01 M dye-doped crystal has the value 12.40 GW/cm2 as compared to 8.59 GW/cm2 for pure crystal, whilst, second harmonic efficiency as observed by Kurtz test decreases on increasing dye concentration such that crystals of pure, 0.001 M and 0.01 M dye-doped have the respective values of 26.4 mV, 18.1 mV and 17.6 mV.

Synthesis and characterization of a metal-organic NLO material: Tetrakis(thiourea)cobalt chloride

We investigate the growth of the hybrid complex tetrakis(thiourea)cobalt chloride (TTCoC) from an aqueous solution of thiourea and cobalt chloride through a slow evaporation method that yields good-quality crystals. Different analyses confirmed that TTCoC crystal is a good nonlinear optical material. The crystal system and parameters were determined by X-ray diffraction analysis, which showed that the crystals crystallize in the tetragonal system with non-centrosymmetric space group P42/n. Within this structure, each Co2+ ion is bordered by four sulfur atoms and two chlorine atoms, which allows it to adopt an octahedral coordination geometry. The functional groups in the complex were confirmed by Fourier transform IR spectroscopy. Furthermore, the percentages of the different elements present in this compound were identified through energy-dispersive X-ray analysis. The UV–visible spectrum confirmed that TTCoC crystal has transmittance as high as 59.6%. The optical band gap energy of TTCoC was obtained from the Tauc plot of (αhν)2 versus hν. Its value is equal to 4.6 eV. Thermogravimetric analysis and differential scanning calorimetry revealed stability up to around 110 °C. The nonlinear optical properties of the crystal were studied by the Kurtz-Perry technique, and the efficiency of its second harmonic generation was found to be equal to that of potassium dihydrogen phosphate single crystal. This result was confirmed by theoretical calculations of the polarizability and the first hyperpolarizability. To determine the closest contacts within the crystal, Hirshfeld surface analysis was performed. Finally, according to the fingerprint plots, we can attribute the dominant interaction present within the structure to hydrogen bonds.

Patterning the Internal Structure of Single Crystals by Gel Incorporation

Single crystals are usually homogeneous, whereas heterogeneous internal structures can be constructed by incorporation of foreign materials. The existence of the homogeneous and heterogeneous states (termed as state “0” and “1”) inspires the idea to transform crystals between them so that the internal structures in the crystals become patternable. Here, gel-grown potassium dihydrogen phosphate single crystals transforming between “0” and “1” states (without and with gel incorporation) are demonstrated by oscillating the crystallization conditions of growth rates (slow for “0”; fast for “1”) or growth media (solution for “0”; gel for “1”). As a result, crystals in the sequences of “010”, “001”, “011”, “100”, “110”, and “101” have been obtained. By showing the patterned structure through gel incorporation, this work presents one more degree of freedom for structural modification of crystals.

A study on fracture toughness of potassium dihydrogen phosphate single crystals

The results of the temperature dependence of fracture toughness of KDP crystals with four orientations show that the brittle-to-ductile transition occurs at 160 °C.

Effect of L-arginine additive on the growth and physical properties of Potassium Dihydrogen Phosphate single crystals

Effect of L-arginine additive on the growth and physical properties of Potassium Dihydrogen Phosphate single crystals

Effect of L-Cysteine doping on growth and some characteristics of potassium dihydrogen phosphate single crystals

Among quite a number of technologically important NLO materials, Potassium Dihydrogen Phosphate (KDP) is one of the most favourable ones for second harmonic generation applications, such as in electro-optic modulators, parametric oscillators and harmonic generators. The authors report here their studies on KDP crystals doped with L-Cysteine (1mol% and 2mol%). The dopant inclusion in the crystals was confirmed using Fourier transform infrared (FT-IR) spectroscopy and Powder X-Ray Diffraction (XRD). The XRD results also confirm the tetragonal structure with lattice parameters a = b = 7.45Å and c = 6.98Å. The presence of functional groups of crystals was analyzed using the FTIR spectra. For band gap evaluation, UV–Vis spectra were used and it was found to be 3.41eV, 4.40eVand 4.50eV, respectively in the cases of pure KDP, 1mol% and 2mol% L-Cysteine dopings. The spectra quality indicates good transparency of the doped crystals in the visible region, a feature quite desirable for applications in optoelectronics.

Enhanced second harmonic generation and photoluminescence in Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass

Non-linear optical properties and photoluminescence exhibited by Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass are presented here. The glasses of composition 1.5Li2O–2B2O3–0.5Nb2O5–0.5Ta2O5:xPr6O11 (x = 0.0025, 0.005, and 0.01) were synthesized via the conventional melt-quenching technique, and the nanocrystal growth was induced by subjecting the as-quenched glasses to heat treatment between 530 and 560 °C for 3 h. Coalesced nanocrystals of sizes in the 20–38 nm range, resulting in the formation of dendritic spherulites, were obtained from the isothermal heat treatment. Effect of doping on the structural units of LiNb0.5Ta0.5O3 lattice was analysed by Raman studies, which indicated that Pr ions occupied Li+ vacancies or Nb/Ta antisites. A strong red emission at 620 nm, due to 1D2 → 3H4 electronic transition of Pr3+ ions, was observed upon excitation by a 450 nm radiation. The maximum intensity was exhibited by the composition corresponding to Pr-doping level, x = 0.005, while the crystallization had a pronounced effect on the intensity of the red output. A non-linear optical coefficient as high as 0.77 pm/V (twice that of d36 of potassium dihydrogen phosphate single crystal) was obtained from the bulk glass–nanocrystal composites of the composition in which x = 0.0025.

Electronic excitation energy transfer and nonstationary processes in KH2PO4:Tl crystals

We report the results of our experimental study and numerical simulation of the electronic excitation energy transfer to impurity centers under conditions where nonstationary processes take place in the hydrogen sublattice of potassium dihydrogen phosphate (KH2PO4) single crystals doped with mercury-like Tl+ ions (KDP:Tl). We present the experimental results of our investigation of the decay kinetics of the transient optical absorption (100 ns–50 s) of intrinsic defects in the hydrogen sublattice of KDP:Tl obtained by pulsed absorption spectroscopy and the results of our study of the dynamics of the change in steady-state luminescence intensity with irradiation time (1–5000 s). To explain the transfer of the energy being released during electron recombination involving intrinsic KDP:Tl lattice defects, we formulate a mathematical model for the transfer of this energy to impurity Tl+ luminescence centers. Within the model being developed, we present the systems of differential balance equations describing the nonstationary processes in the electron subsystem and the hydrogen sublattice; provide a technique for calculating the pair correlation functions Y(r, t) of dissimilar defects based on the solution of the Smoluchowski equation for the system of mobile hydrogen sublattice defects; calculate the time-dependent reaction rate constants K(t) for various experimental conditions; and outline the peculiarities and results of the model parametrization based on our experimental data. Based on our investigation, the dramatic and significant effect of a gradual inertial increase by a factor of 50–100 in steady-state luminescence intensity in the 4.5-eV band in KDP:Tl crystals due to the luminescence of mercury-like Tl+ ions has been explained qualitatively and quantitatively.

Vickers Microhardness Studies of Pure and Amino Acids Doped Potassium Dihydrogen Phosphate Crystals

Vickers microhardness study was carried out to understand the mechanical behaviour of pure and different amino acids (L-arginine, L-lysine, L-alanine) doped potassium dihydrogen phosphate (KDP) single crystals grown by slow solvent evaporation technique. Indentations were made on smooth {100} plane of pure and different amino acid doped crystals for loads varying from 0.298 N to 0.98 N. Vickers microhardness decreased as doping level of amino acid was increased. Indentation size effect (ISE), Kick's law, Hays and Kendall's law and Proportion specimen resistance (PSR) model were verified for pure and different amino acids doped crystals. The values of the load independent hardness and Newtonian pressure were higher in pure KDP crystals than the amino acids doped KDP crystals. It was found that as doping concentration of amino acids increased the load independent hardness and Newtonian pressure decreased. The results indicated that the doping of amino acids made KDP crystals softer.