Up‐conversion Luminescence in Dye‐Doped Crystals of Potassium Hydrogen Phthalate

Abstract

can be independently adjusted. Shown in Figure 3e is one example of using a size-reduced nanopillar for nanoimprinting. In this case, the size of nanopillars was reduced using a chromium etchant. The lateral dimension of the imprinted holes was less than 30 nm. Other approaches to size reduction are currently under investigation in our group.In summary, we have developed a low-cost, high-throughput fabrication process for producing large-area, well-ordered periodic nanopillars for nanoimprinting with feature size less than 50 nm that would allow the nanoimprinting technique to be easily accessed without the need for e-beam lithography. When these stamps are used in nanoimprint lithography, large-area periodic nanostructures with lateral dimensions less than 30 nm can be obtained. The size and separation of the fabricated periodic nanostructures can be independently adjusted by selecting different diameters of polystyrene beads in the nanosphere lithography step and by trimming the nanopillars using various size reduction techniques, respectively. The shape of the nanostructures can also be modified by using different combinations of metal masks and etching recipes. ExperimentalNanopillars: To fabricate silicon nanopillars, 1 1 cm 2 substrates cut from ndoped silicon (100) wafers (Gredmann) were used. These silicon substrates were cleaned by immersion in piranha solution (3:1 concentrated H 2 SO 4 / 30 % H 2 O 2 ) and sonication for 30 min. After sonication the substrates were rinsed repeatedly with ultrapure water (18.2 MX, Millipore Simplicity), acetone, and methanol and used immediately. To produce metal masks for the nanopillar array, nanosphere lithography was employed. Details of the nanosphere lithography procedure can be found in the literature [21,22]. In short, monodispersed polystyrene beads of various diameter purchased from Bangs Laboratories, Inc. (Fishers, IN) were diluted in a solution of surfactant Triton X-100 (Aldrich) and methanol (1:400 by volume). This solution was then spin-cast onto substrates to form hexagonally closed-packed 2D colloidal crystals. Depending on the experimental requirements (single or double layer), the speed of spin-coater was varied between 800 and 3600 rpm (~1500 rpm for a double layer), and the dilution ratio of the polystyrene solution was also changed. It was found that the formation of self-assembled 2D colloidal crystals strongly depended on the speed of spin-coater. These 2D colloidal crystals were then used as the deposition templates. A 50 nm thick Cr film was deposited over the polystyrene masks at a rate of 15 nm min ±1 in an ULVAC vapor deposition system at a pressure of 1 10 ±3 Pa. After Cr deposition, the polystyrene beads were removed by sonicating the substrates in CH 2 Cl 2 solution for 3±5 min. To fabricate silicon nanopillar arrays, substrates with metallic masks were placed in a reactive ion etcher (Oxford Plasmalab 80 Plus, 80 W) with a gas mixture of CHF 3 (20 sccm) and O 2 (2 sccm) at a total pressure of 25 mtorr. The nanopillars used for nanoimpri...

Dispersive Kinetics from Single Molecules Oriented in Single Crystals of Potassium Acid Phthalate

“…The enhancement in τ f for 1 in KAP compared to solution is consistent with a decrease in excitedstate internal conversion due to the conformational restrictions provided by the host lattice, as reported for other dye-inclusion KAP crystals. 21 The ensemble-averaged orientation of the absorption transition dipole moment of 1 in heavily dyed KAP/1 was determined by polarized absorption microscopy to be 41.8 ( 1.6°from [100] in the ac-plane. Single-molecule measurements on KAP/1 established that the average orientation for 200 molecules was 41.5 ( 14.0°(one standard deviation from the mean), in agreement with the bulk measurement.…”

“…The photoexcitation rate constant (k 12 ) is restricted to 1 × 10 6 s -1 on the basis of the experimental laser power and absorption cross section of 1. The radiative rate constant (k 21 ) is fixed at 3.7 × 10 8 s -1 consistent with the measured fluorescence lifetime of KAP/1. To account for power-law behavior, the dark-state population (k 23 ) and depopulation (k 31 ) rate constants were modeled as follows:…”

“…In addition, molecular bleaching due to photooxidation is reduced relative to oxygen-permeable matrices, and the decrease in nonradiative relaxation caused by the restrictive environment affords enhanced photostability. 21 Although traditional attempts to incorporate chromophores into host crystals have been limited to the regime where the host and guest are isomorphous, 22,23 we have demonstrated the use of potassium acid phthalate (KAP) 21,24 and K 2 SO 4 25,26 matrices to study a variety of organic dye molecules in the regime of nonisomorphous incorporation.…”

Growth and characterization of NLO crystal: L-leucine phthalic acid potassium iodide

“…Phthalate crystals are often used as diffracting crystals since they can be easily cleaved and are potential candidates for many device applications [13][14][15]. The study on crystal growth of potassium iodide crystal obtained by solution growth method revealed the reduction in the impurity concentration compared to melt growth technique [16]. Hence, in this paper, it is reported on the synthesis and growth of Lleucine phthalic acid potassium iodide single crystal followed by characterizations, like XRD, FT-IR, TG-DTA, UV, EDAX, SEM.…”

Influence of Xylenol Orange Dye on Optical, Thermal, Dielectric, Laser Damage Threshold and Mechanical Properties of L-Alanine Thiourea (LATU) Single Crystals

“…Among these the second harmonic generation efficiency (SHG) of glycine Thiourea crystal was 0.5 times that of KDP crystal, the SHG efficiency of L-Histidine Thiourea crystal 4.1 times that of KDP crystal and Methylene blue admixtured LAlanine Thiourea crystal 1.56 times that of KDP crystal. Many researchers have worked on dye admixtured potassium dihydrogen phosphate and potassium acid phthalate nonlinear optical crystals in order to improve their nonlinear response [13,14]. Xylenol orange [3, 3" bis [N, N"-Di(carboxymethyl) -aminomethyl -O -cresolsulphone -phthalein tetrasodium salt] (XO), a heterocyclic species which belongs to the acidic class of dyes.…”