Extensive work has been reported on making nanometre sized phosphors to keep up with continuing trends of high
resolution displays and nanotechnology. However most of these nanophosphors suffer from surface agglomeration.
Thus, a novel method has been developed to prepare discrete phosphor nanoparticles. The precursor phosphor powders
obtained from solution by the urea precipitation method were coated with silica. Coating with silica before firing the
precursor avoids sintering the particles which occurs when the precursors are fired to convert them into phosphors. The
coated precursors were fired with ethanol at desired temperatures to get core-shell particles consisting of nanophosphor
cores in silica shells. The silica coating was removed by washing with NaOH solution to liberate discrete phosphor
nanoparticles. The particle size analysis results of these discrete phosphors show a narrow particle size distribution in the
sub-micrometre range. The emission and excitation spectra have been obtained, and compared with those of commercial
phosphors. These nanophosphors can be incorporated into printable ink formulations and might find applications in high
resolution display devices.
A handheld gas detector is being developed that consists of a laser diode emitting light of wavelength equal to 1651 nm and an extended InGaAs detector. The IR laser beam is double-passed through a column of air via a folding mirror to a detector. The air column is in contact with the outside atmosphere so that low-relative-molecular-mass hydrocarbon gases, which diffuse into the air column, can be detected by the absorption of some of the IR light. The absorption at around 1651 nm is due to the overtones of C—H stretching vibrations and the limit of detection of the technique is at the parts per million level. One of the problems of using such a device in the field is that the operator cannot visualize the IR beam directly. Consequently, if the gas detection device fails to give a reading, the operator cannot be sure whether the laser is emitting light and the beam is correctly aligned. We describe the use of a novel phosphor screen to visualize the beam by converting the IR radiation into visible light. The properties of a number of phosphors that were developed and tested for the visualization of the beam are described. The merits of storage phosphors are compared to those of upconversion phosphors for use at this wavelength, which is longer than wavelengths previously visualized using upconversion phosphors.
A broad-band green light source for a head-up display is presented. To our knowledge, this is the first report of a green phosphor screen being excited by a blue LED as a backlight for monochrome HUDs. The phosphor screen not only generates the green light but it acts as a diffuser to give a homogeneous illumination. A microlens array focuses the emissions from LED sources on to the diffusing screen eliminating halo effects from the individual LEDs. The purpose of using a green phosphor is to exploit the fact that the eye is sensitive to more shades of green than any other colour. In uses where there are elements of danger such as automobiles (in busy areas), vehicles on construction sites and military vehicles in war zones, green displays have obvious attractions. This paper presents a discussion of the green phosphors that can be used in green screen fabrication, the deposition of the phosphor powders on the screens, the influence of the thickness of the phosphor powder on the screen brightness. In addition, the factors that influence the CIE coordinates of the light emitted from the screen are considered. The importance of choosing the optimum LED emission wavelength along with the general construction of the HUD is discussed. The merits of using a green screen are compared to those when using full colour displays based on white phosphor screens in which yellow emitting phosphors are excited by blue LEDs. Heat management in these HUD devices is achieved by pulsing the LEDs and rastering rows within the LED array.
A hand held gas detector is being developed that consists of a laser diode emitting light of wavelength equal to 1651 nm and an extended InGaAs detector. The infrared laser beam is double-passed through a column of air via a folding mirror to a detector. The air column is in contact with the outside atmosphere so that low relative molecular mass hydrocarbon gases, which diffuse into the air column, can be detected by the absorption of some of the infrared light. The absorption at around 1651 nm is due to the overtones of C-H stretching vibrations and the limit of detection of the technique is at the parts per million level. One of the problems of using such a device in the field is that the operator cannot visualise the infrared beam directly. Consequently if the gas detection device fails to give a reading, the operator cannot be sure whether the laser is emitting light and the beam is correctly aligned. The paper describes the use of a novel phosphor screen in order to visualise the beam by converting the infrared radiation into visible light. The properties of a number of phosphors that were developed and tested for the visualisation of the beam will be described. The merits of storage phosphors are compared to those of upconversion phosphors for use at this wavelength, which is longer than wavelengths previously visualised using upconversion phosphors.
A band at ca. 150 cm-1 in the far infrared spectrum of diketopiperazine (DKP) is assigned to a ring puckering vibration. The multiplet structure reported for this band in the low temperature (77 K) far IR spectrum can be interpreted if the vibration is assumed to have quartic character. By means of Rayleigh-Schrodinger perturbation theory, a new vibrational selection rule, (Delta) n equals +/- 1, +/- 3, has been derived for mixed quartic-quadratic vibrations in the near harmonic region for the case of zero electrical anharmonicity. Assignments of the multiplet components have been made in the light of this vibrational selection rule. A two-parameter potential energy function of the ring puckering coordinate has been derived for the DKP molecule. This has enabled a value of ca. 355 cm-1 to be estimated for the energy barrier to interconversion of enantiomeric boat forms of DKP. The 0 - 1 transition has been estimated to have a wavenumber value of 0.033 cm-1 (1 GHz) in excellent agreement with the value of approximately 1 GHz obtained from a gas phase microwave spectroscopic study.
These portrait miniatures on ivory were analyzed by Raman microscopy to determine the identity of tiny, white crystals which occur under, within, or on top of their paint layers. In each case the crystals were identified as magnesium hydrogen phosphate trihydrate, newberyite (MgHPO4.3H2O). Small, white crystals which grow on the inner surface of ivory tusks were also identified as newberyite by means of Raman microscopy. Thus, it is concluded that the tiny, white crystals occurring on the portrait miniatures on ivory almost certainly originate from the ivory substrate. Resonance Raman spectroscopy using 632.8 nm excitations were found to be a sensitive probe for the detection of the blue pigment, indigo, even when it occurs in pigment mixtures on paintings. Raman microscopy was also used in analyze a fragment of opaque red Assyrian glass, dating from around the 9th-8th centuries BC, an opaque red Iron Age glass stud, dating from around the 1st century BC, and three opaque yellow Anglo-Saxon glass beads, dating from the 6th century AD.