Properties of defects induced by irradiation with a near-infrared femtosecond laser into a series of synthetic fused silicas containing different OH contents are reported. Comparing with the samples before laser irradiation, two absorption bands centered around at 4.8 and 5.8 eV which correspond to E'(≡Si•) center and non-bridging oxygen hole center (NBOHC, ≡Si--O•), respectively, were evidently observed after laser irradiation in high-OH silicas. A photluminescence band with photon energy of 1.9 eV was observed in the as-irradiated silicas under 4.8 eV light excitation. Though no red photoluminescence was observed after irradiated inside low OH-containing silica samples, a similar phenomenon occurs when the laser beam was focused near the surface of low-OH silicas. The induced structures were relaxed after annealing at 400°C. A possible model for the generation of 1.9 eV photoluminescence induced by ultrashort pulse laser in wet silicas and dry silicas was proposed.
When rare earth-doped oxyfluoride glasses are heat-treated at the first crystallization temperatures, the glasses turn into glass-ceramics in which rare earth-containing nanocrystals uniformly precipitate in the glass matrices. These glass-ceramics are transparent to the naked eye as well no heat-treated glasses. Since rare earth ions exist as solid-solution ions in the precipitated fluoride crystals with low phonon energies, these glass-ceramics exhibit highly efficient up-conversion luminescence by laser light excitation. In the present work, rare earth-doped oxyfluoride glass-ceramics in the SiO2-PbF2-HoF3-YbF3-GdF3, and SiO2-PbF2-TmF3-YbF3-GdF3 systems were developed. Under 980nm LD excitation the respective glass-ceramics gave selectively red-, green-, and blue-upconversion luminescence with high efficiency. Emission wavelengths in the center of gravity are 666, 543, and 479 nm, respectively. Except for these selective emissions, however, other emissions at different wavelengths are also observed, though extremely weak. Removal of these extra emissions was possible by using appropriate filter-glasses, presenting the up-conversion devices of individual emission of red (R), green (G), and blue (B). On the other hand, laminas of the mixtures of resin and the glass-ceramic powders exhibited extremely high enhancement of upconversion emission intensities. The developed upconversion glass-ceramics in which RGD emissions are independently available by 980 nm laser irradiation offer a variety of applications. Some of the expected utilization as optics devices is proposed.
Oxyfluoride glasses of the compositions of 50SiO2•50PbF2•(5 - x)GdF3•xErF3 and 50SiO2•50PbF2•(5 - y)GdF3•0.1NdF3•yYbF3•0.1(Tb, Ho, Er or Tm)F3 in molar ratio (x =0.3 - 5 and y = 0 - 5) were developed. The oxyfluoride glasses were heat-treated at their first crystallization temperatures. Consequently, the crystals of -PbF2:(trivalent rare-earth ions) solid solutions uniformly precipitated in the scales of 15 20 nm in diameter in silicate glass matrices. These glass-ceramics were transparent to the naked eye. The glass-ceramics gave highly efficient upconversion luminescence based on the Tb3+, Ho3+, Er3+ or Tm3+ ion under 800 and/or 980 nm light excitation. These oxyfluoride glasses can be locally changed to glass-ceramics in the forms of dots, lines, letters, planes, etc. by irradiation of various lasers. The forms written by laser irradiation can be easily read from upconversion luminescence generated by the 800 and/or 980 nm laser illumination. Thus, the present oxyfluoride glasses can be applied to an optical memory device for specific information. Plates, fibers, thin films and coating-films in which the glass-powders are embedded in inorganic and/or organic polymers are considered as the shapes of oxyfluoride glasses that can be utilized as the device.