Spectral sensitivity and photoresponse in the rock bream Oplegnathus fasciatus and their relationships with the absorption maximum of the photoreceptor.

The spectral characteristics of visual pigments are a major determinant in eliciting a response to light. To study the absorption maximum of the photoreceptors and their sensitivity to light in fish, rod outer segments (ROS) and cone cells were purified from the rock bream Oplegnathus fasciatus adapted to the dark. Ultraviolet/visible spectroscopic analyses of the ROS in the dark and its difference spectra indicated an absorption maximum of the visual pigment at ~ 500 nm, and each eye of 1-year-old rock bream contained at least 1.2 nmol of rhodopsin-like visual pigments. Microspectrophotometric analysis of the cone cell outer segments led to identification of three visual pigments with individual absorption maxima at 425, 520, and 585 nm. Monochromatic light-emitting diode (LED) modules with different wavelengths (violet 405 nm, blue 465 nm, cyan 505 nm, green 530 nm, amber 590 nm, and red 655 nm) were constructed to examine the spectral sensitivity and photoresponse in association with the absorption maximum of the photoreceptor. Analysis of chromophore decay upon illumination with each LED at low (27 µmol/m2/s) and high (343 µmol/m2/s) intensities showed the highest sensitivity of the photoreceptor upon illumination with the 505-nm cyan LED, followed by LEDs with wavelengths of 530 nm > 465 nm > 405 nm > 590 nm > 655 nm. Photoresponse analysis of the fish using a video tracking system, in the dark and upon illumination, also showed faster movement of fish with illumination with the cyan LED followed by in the order of green ≈ blue > violet > amber > red. These results indicated that a light with a wavelength closer to the absorption maximum of rhodopsin was more effective in eliciting a response to the light.

Dim-light photoreceptor of chub mackerel Scomber japonicus and the photoresponse upon illumination with LEDs of different wavelengths.

To study the absorption characteristics of rhodopsin, a dim-light photoreceptor, in chub mackerel (Scomber japonicus) and the relationship between light wavelengths on the photoresponse, the rod opsin gene was cloned into an expression vector, pMT4. Recombinant opsin was transiently expressed in COS-1 cells and reconstituted with 11-cis-retinal. Cells containing the regenerated rhodopsin were solubilized and subjected to UV/Vis spectroscopic analysis in the dark and upon illumination. Difference spectra from the lysates indicated an absorption maximum of mackerel rhodopsin around 500 nm. Four types of light-emitting diode (LED) modules with different wavelengths (red, peak 627 nm; cyan, 505 nm; blue, 442 nm; white, 447 + 560 nm) were constructed to examine their effects on the photoresponse in chub mackerel. Behavioral responses of the mackerels, including speed and frequencies acclimated in the dark and upon LED illumination, were analyzed using an underwater acoustic camera. Compared to an average speed of 22.25 ± 1.57 cm/s of mackerel movement in the dark, speed increased to 22.97 ± 0.29, 24.66 ± 1.06, 26.28 ± 2.28, and 25.19 ± 1.91 cm/s upon exposure to red, blue, cyan, and white LEDs, respectively. There were increases of 103.48 ± 1.58, 109.37 ± 5.29, 118.48 ± 10.82, and 109.43 ± 3.92 %, respectively, in the relative speed of the fishes upon illumination with red, blue, cyan, and white LEDs compared with that in the dark (set at 100 %). Similar rate of wavelength-dependent responses was observed in a frequency analysis. These results indicate that an LED emitting a peak wavelength close to an absorption maximum of rhodopsin is more effective at eliciting a response to light.

Triple-layered perovskite niobates CaRNb3O10 (R = La, Sm, Eu, Gd, Dy, Er, Yb, or Y): new self-activated oxides.

Niobates CaRNb3O10 (R = La, Sm, Eu, Gd, Dy, Er, Yb, or Y) were prepared by conventional high-temperature solid-state reaction. The formation of a single-phase compound with triple-layered perovskite-type structure was verified through X-ray diffraction (XRD) studies. The luminescence characteristics such as photoluminescence excitation and emission spectra, X-ray-excited luminescence (XEL), Stokes shift, decay curves, and color coordinates were investigated. The niobates can be efficiently excited by UV light and present luminescence behaviors with rich luminescence colors. Under excitation by ultraviolet radiation, CaRNb3O10 (R = La, Gd, Yb, or Y) exhibits strong blue luminescence due to the self-activation center of the octahedral NbO6 groups, even at room temperature. For the materials of composition CaRNb3O10 (R = Sm, Eu, Dy, or Er), the excitation at the host band produces a characteristic luminescence of rare earth ions, indicating a host-guest energy transfer process. CaRNb3O10 (R = Eu) has the strongest luminescence intensity, which can be efficiently excitated by near UV wavelength. It could be suggested to be a potential candidate for the application on near-UV excited white LEDs.

Novel yellow-emitting phosphors of Ca5M4(VO4)6 (M=Mg, Zn) with isolated VO4 tetrahedra.

The self-activated yellow-emitting phosphors of vanadates Ca5M4(VO4)6 (M = Mg, Zn) were synthesized via the solid-state reaction route. The formation of single phase compound with garnet structure was verified through X-ray diffraction (XRD) studies. The excitation and emission spectra and the thermal quenching of luminescence intensities were measured. The different luminescence properties of Ca5Mg4(VO4)6 and Ca5Zn4(VO4)6 phosphors were presented, e.g., the spectra shift, the luminescence lifetimes, the absolute quantum efficiency, the color coordinates and the Stokes shift. This deference was discussed on the base of the relationship between the micro-structure and the charge transfer transitions in [VO4]3- groups in the lattices. Ca5Mg4(VO4)6 could be suggested to be a potential yellow-emitting phosphor for the application on near-UV excited white LEDs.