Rare earth-doped oxyfluoride glass of the 50SiO2 -50PbF2 -5ErF3 composition in molar ratio was developed. When the oxyfluoride glass is heat-treated at the first cystallization temperature, the glass gives the glass-ceramic in which rare earth-containing fluorite-type nanocrystals of about 20 nm in diameter uniformly precipitate in the glass matrices. The glass-ceramic is trasnparent to the naked eye like no heat-treated oxyfluoride glass. The glass-ceramic exhibits highly efficient upconversion luminescence under 800 and/or 980 nm laser light excitation.
On the other hand, the oxyfluoride glass can be locally changed to glass-ceramic in the forms of dot, line, plane, letter, etc. by thermal energies generated from light absorption of various lasers. In the case of CO2 laser irradiation the formation of such glass-ceramic occurs near the surface of glass. In the case of 800 or 980 nm irradiation by Ti:sapphire laser or laser diodes, on the other hand, the formation of such glass-ceramic occurs near the surface and/or inside of glass. The glass-ceramic parts can be easily read by upconversion luminescence under laser excitation. Therefore, the presently developed rare earth-doped oxyfluoride glass can be utilized as optical devices of the writing and reading memory, which can be utilized as specific devices for security information.
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.
Compositions which vitrify by means of a conventional glass melting method, containing a large amount of erbium ion were investigated in aluminosilicate, phosphate, borate, borosilicate, telluride and fluoride systems. As a result of melting test, we obtain some glasses which contain higher than 20 mol% erbium. In transparent materials containing erbium an anomalous optical absorption phenomena have been reported by Maeda et al. With increasing in an incident laser light intensity, the transmitted one through the transparency such as the glass decreases, that is called negative nonlinear absorption (NNA) effect. With a particular modulation degree of an incident laser light, the transmitted waveform were reversed in phase to an incident one. The NNA effect in these glasses was observed over a wide band of the wavelength, while in erbium doped yttrium aluminum garnet and erbium doped lutetium aluminum garnet crystals were observed at a narrow band. The discrepancy of the NNA effect between the glasses and the crystals might be explained in the term of absorption spectrum associated with erbium. Namely, the absorption spectra of erbium doped yttrium aluminum garnet crystal have a narrow absorption band of 788 nm, while that of the glasses have broad absorption band of about 800 nm.
An all-optical inverter, which operates over a temperature range of -200 to 750 degree(s)C, was demonstrated in erbium- doped borate glass. The dependence of negative nonlinear absorption effect on sample temperature and modulation degree was investigated, using an 810.0 nm laser diode. Reversed-phase waveforms were observed in the transmitted waveform in the temperature range. The glass transition temperature was measured to be 708 degree(s)C by differential thermal analysis. With a decreasing modulation degree, the reversed-phase waveform was obtained. The effect has a characteristic which is almost independent of the sample temperature because it is formed by optical transitions of the inner shell of the erbium ion.
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