Journal of the Society for Information DisplayVolume 8, Issue 1 p. 1-1 Introduction Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author First published: 18 June 2012 https://doi.org/10.1889/1.1828693Citations: 13AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume8, Issue1March 2000Pages 1-1 RelatedInformation

There are many reports in the literature of a spectral difference between the triboluminescence (TL) spectrum and the solid-state photoluminescence (PL) spectrum of the same compound. Numerous reasons have been suggested for this difference including pressure-induced changes to Franck-Condon factors during the lifetime of the TL light emission; self-absorption of the TL emission and fracture-induced symmetry changes perturbing the local field of the TL emitting species. However, in a number of cases, the luminescent spectra were recorded on different equipment with different spectral responses, with the resolution of either luminescent spectrum rarely quoted. To avoid artificial spectral differences, care must be taken to account for the response of each equipment over the wavelength range studied, as well as any resolution difference. We have therefore measured the TL and solid-state PL spectra of sixteen TL compounds on the same spectrometer at an identical resolution. Furthermore, the solid-state photoluminescent lifetime has been determined for all samples and the implication that these values have for observing pressure-induced (Franck-Condon) luminescent spectral changes discussed. Finally, in all cases where a significant difference was observed between TL and PL spectra, either self-absorption of the TL emission or fracture-induced perturbations of the local field have been evoked to explain the difference.

Some new donor–acceptor porphyrins have been prepared based on a metallated bis(ethynyl) porphyrin core. 4-(Dimethylamino)phenyl was used as the donor group and 4-nitrophenyl, 4-cyanophenyl and 5-nitrothiazoyl as the acceptor groups. Dipyrrylmethane was used for large scale porphyrin ring synthesis because the absence of methylene substituents reduces the difficulty of substituent scrambling that occurs during porphyrin synthesis.

Phthalocyanines solubilised by either 8 or 16 aryloxy or haloaryloxy groups are described. A series of phthalocyanine derivatives were prepared containing indium. 1,2-Dinitriles and the corresponding diiminoisoindolines were used as precursors. A naphthalocyanine metallated with indium and solubilised with four tert-butyl groups is reported.

A series of ethynyl and aryl substituted porphyrins and the corresponding metallated derivatives have been synthesised and characterised.

Ground rules defining design of triboluminescent (TL) materials are currently missing, in part since the triboluminescent efficiency is the product of the efficiency of excited-state formation and the efficiency of radiative relaxation from these excited-states. In order to de-couple these two processes, we have measured, for the first time, the solid-state photoluminescent quantum yield of various triboluminescent materials. The measurements highlighted: (i) some triboluminescent materials possess near-optimised radiative yields; (ii) structurally similar triboluminescent compounds can exhibit widely varying yields and (iii) some triboluminescent materials, which appear to the eye as reasonably efficient, possess low radiative yields, allowing possible triboluminescent enhancement.

Triboluminescent materials have been known for at least four centuries. The majority of work to date has been academic in nature - reporting a new triboluminescent material and/or presenting a spectroscopic study in an effort to explain the mechanism underlying the fracture-induced light emission. Recently, the advantages of triboluminescent materials as real-time structural damage sensors have been highlighted. These sensors can be exploited in both commercial and military markets. In addition to covering some of the recent advances in the field, this paper aims to provide a timely overview of those triboluminescent materials which may be suitable as structural damage sensors.

Indium porphyrin 1 is an excellent optical limiterat visible wavelengths (480–620 nm). Absorption of light results in quantitative formation of the triplet excited state, which absorbs light 48 times more strongly than the ground state and has a lifetime of 0.8 ms. This should provide strong nonlinear attenuation of laser pulses on picosecond to microsecond timescales.

The response of organic dyes to laser pulses is typically described solely by nonlinear absorption. Recently, spatial profiles of a nanosecond pulse exiting an organic nonlinear absorber have shown energy redistribution from a Gaussian input profile to a central spike and outer ring. It was suggested that the spike and ring resulted from both nonlinear absorption and nonlinear refraction. In this letter, the role of a thermal nonlinear refraction in beam shaping is demonstrated using single and time-delayed double picosecond pulses. It is concluded that the dynamics of nonlinear absorption and nonlinear refraction must be included to correctly describe the laser-material interaction.

In a reverse saturable absorbing dye the absorption coefficient gets greater as the dye absorbs more light. In some of these dyes, where triplet state absorption dominates, the absorption coefficient can change by more than a factor of 10 in response to the laser fluence, F(J/cm/sup 2/). Organic macrocyclic dyes such as porphyrins, phthalocyanines and naphthalocyanines have this property and have been studied extensively over the last decade. In order to understand the effects of the various contributing photo-physical processes, detailed beam propagation models have been developed. These have usually concentrated on modelling the interaction of a weakly focused laser beam with a thin sample but more recently interest in the low threshold tight focusing geometry has increased. The interaction of a tightly focused beam with a non-linear material exhibits some unusual effects. This paper describes how these effects may be modelled using ray optic Monte-Carlo methods and more accurate beam propagation techniques. The evolution of the nonlinear absorbing region within the sample is modelled using both methods. Both approaches reveal the growth of two distinct regions of high absorption within the laser beam and the nonlinear transmission curves obtained in the two cases agree well.

A linear zinc porphyrin dimer has been used for the first time to stabilise two identical non-covalent aggregates by a combination of N-pyridyl zinc binding and hydrogen bonding. An improved multigram synthesis of 5,15-bis-(3,5-di-tert-butylphenyl)-10,20-bis(trimethylsilylethynyl)porphyrin is described.

Nine structurally related porphyrins are studied and it is shown how the material parameters that control the optical limiting depend on the molecular structure. Optical limiting measurements at 532 nm on the metal-free, zinc and lead analogues of tetraphenyl porphyrin (TPP), tetra(trimethylsilyethynyl) porphyrin (TTMSAP) and tetra(4-n-butylphenylethynyl) porphyrin (TNBBAP) reveal a strong dependence on the metal atom and peripheral substitution. A double pump/cw probe technique is used to measure the material parameters that control the optical limiting and the results give a strong insight into how the molecular structure influences the individual parameters. These measurements revealed that one of the materials TTMSAP(Pb) has a σex/σgr ratio of ~45 at 532 nm, which is one of the largest values ever reported. Finally, broadband measurements with a picosecond white-light source show that the position and strength of the excited state absorption features also depend strongly on the porphyrin design.

Shadowgraphs taken at four wavelengths indicate varying amounts of excited-state absorption in the focusing cone of a laser pulse within a sample of C60 in PMMA. The images provide information on the location and strength of excited-state absorption, and allow verification of excited-state lifetimes. Importantly, the transverse images provide direct experimental support for the role of both nonlinear refraction and nonlinear absorption in leading to a spatial redistribution of energy within the material. The technique, results and implications for modelling the laser–material interaction are briefly discussed.

The spatial redistribution of energy resulting from the interaction between a near-diffraction-limited nanosecond laser pulse and the nonlinear absorbing optical limiting dye silicon naphthalocyanine is described, for what is to our knowledge the first time, in an optical geometry that is likely to be found in practical applications. For input fluences above that required for nonlinear absorption but below that for bubble growth, a plane wave or Gaussian spatial input evolves unexpectedly to a sharp central spike and a well-defined outer ring. The observed energy redistribution is thought to rely on a combination of nonlinear processes, since a pure absorptive process alone cannot explain the profiles presented. A model involving nonlinear absorption and nonlinear refraction qualitatively reproduces the observed spatial profiles. It is clear from the results that the performance of optical limiting dyes in representative optical geometries, even at fluences well below that required for bubble growth, cannot be described solely by nonlinear absorption.

Currently, there are no simple sensing techniques for determining in real-time both the severity and location of structural damage in a composite caused by a dynamic impact event. Materials are known which emit light when they are fractured. This fracture-induced light emissions is known as triboluminescence. A triboluminescent material embedded in, or attached on, a composite structure could act as a real- time damage sensor. The occurrence and severity of the damage is given by the intensity of the resulting triboluminescent light. Since the triboluminescent light emission is fracture-initiated, no signal would be generated by a triboluminescent sensor until damage had actually occurred. Hence no false alarms are generated by this type of sensor. An array of triboluminescent sensors may allow real-time damage location monitoring simply by determining the wavelength of the emitted light. We have developed a series of highly efficient triboluminescent materials with sufficient thermal and chemical properties to allow doping into composites. We report a series of proof-of-principle experiments with these materials which strongly support the potential of triboluminescent sensors to monitor in real- time both the magnitude and location of structural damage.

The organic crystal 4-nitro-4′-methylbenzylidene aniline (NMBA) was identified as a promising nonlinear material by the powder technique. The material gave a second harmonic intensity 16 times that of urea. Large single crystals of dimensions 5×3×1 cm3 were grown by the temperature lowering of a seeded supersaturated ethyl acetate solution. The principal dielectric axes were defined by orthoscopic examination. The dispersions of the refractive indices were determined to an accuracy of ±0.0015 using the minimum deviation technique and Maker fringe spacings. These dispersion curves were fitted to a Sellmeier equation which allowed the indices to be determined to ±0.0006. The nonlinear d coefficients d11, d33, d31, and d13 were evaluated at 1000, 1064, and 1300 nm using the Maker fringe technique. The coefficient d11 was over 200 times larger than potassium dihydrogen phosphate (KDP) d36. In addition, the nondiagonal coefficient d31 was similar to the phase-matching coefficient in the organic material 3-acetamido-4-dimethylamino-nitrobenzene (DAN). Critically phase-matched second harmonic signals were observed at all fundamental wavelengths. There was excellent agreement between the experimentally determined and theoretical phase-matched incidence angles. Noncritical phase-matched conditions have been calculated and are reported. Both angle and wavelength noncritical phase matching is possible with this crystal.

The nonlinear optical effects of chlorophyll ‘a’ have been determined using an array of measurement techniques. Regions of spectral interest exhibiting induced excited state absorption were identified with transient absorption spectroscopy measurements. At specific wavelengths within these regions, the dye was characterised using the Z-scan technique. Additional measurements were made to complement the latter results including a focused aperture experiment in which thermal defocusing and scattering mechanisms were identified.

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Chromophores containing the tricyanoquinodimethane acceptor moiety possess substantially larger second-order optical nonlinearities than, and similar thermal stabilities to, analogous chromophores bearing the strong tricyanovinyl acceptor.