S. Komuro

Thermally Stimulated and Photostimulated Luminescence from Long Duration Phosphorescent SrAl2 O 4 : Eu , Dy Crystals

The traps in long duration phosphorescent SrAl 2 O 4 :Eu 2+ , Dy 3+ crystals have been evaluated using thermally stimulated luminescence and photostimulated luminescence (PSL) techniques. Afterglow phosphorescence is not observed at temperatures lower than 150 K. Traps with depths of E t,TSL = 0.0024, 0.46, and 0.49 eV are detected by thermally stimulated luminescence techniques. Photostimulated luminescence evaluations reveal that trapped carriers can be released optically using an infrared laser with E t,PSL = 0.55 eV. The trap at E t,PSL = 0.55 eV detected by the PSL may be correlated with the shallow trap levels at E t,TSL = 0.0024 eV.

Characteristics of sapphire fiber connected with ruby sensor head for the fiber-optic thermometer applications

The influences of fiber materials on the performance of the fiber-optic thermometers are evaluated using the thermal probes, in which the sapphire fiber and/or the silica fiber was connected mechanically with the ruby sensor head. The value of photoluminescence (PL) lifetime and its temperature coefficients for the ruby sensor head with sapphire fiber (/spl tau/ = 3.9 ms and -9.9 /spl mu/s/K) were slightly different from those using the silica fiber (/spl tau/ = 4.2 ms and -10.9 /spl mu/s/K), due to the background PL from the sapphire fibers. The influence of the PL from the sapphire fiber on the temperature measurements can be reduced successfully using a modified lifetime calculation based on the curve fitting of the PL decay with double exponential equation.

Characteristics of chromium doped spinel crystals for a fiber-optic thermometer application

Thermometer probe using the chromium doped spinel crystals, MgAl/sub 2/O/sub 4/:Cr/sup 3+/, has been fabricated and the wavelength dependences of PL lifetime are evaluated as compared with those using ruby crystals. Lifetimes and temperature coefficients of the spinel crystals (/spl tau/=10 ms, 37 /spl mu/s/K), which were typically 3 times larger than that of the ruby crystals (/spl tau/=4 ms, 10 /spl mu/s/K), varied from 4.74 ms to 1.65 ms with wavelength from 667.5 nm to 780 nm.

Fabrication of ruby phosphor sheet for the fluorescence thermometer application

A fluorescence thermometer using the temperature dependence of the phase shift of fluorescence response was developed using a ruby phosphor sheet. The ruby phosphor sheet was compounded of ruby powder and silicone resin. The fluorescence lifetime from the ruby phosphor sheet was measured with a phase shift measurement technique. The phase shift of the fluorescence response from the ruby phosphor sheet decreased linearly with temperature from 270to350K. The ruby phosphor sheet is found to be powerful tool for temperature measurement, and can be used for noncontact temperature measurement.

Fluorescence thermometer based on phase angle measurement

Fluorescence thermometer based on the temperature dependence of phase angle of fluorescence pulse was developed using long afterglow SrAl2O4:Eu,Dy and SrAl2O4:Eu,Nd phophors as the sensor materials. Phase angle sensitively varies with temperature. The phase angle measurement technique is potentially useful for the temperature sensing using long afterglow phosphors with extremely high sensitivity.

Development of Sensor Materials in Fluorescence Thermometer

Various sensor materials are developed and evaluated for fluorescence thermometer applications. Sensor materials such as ruby (Al₂O₃), YALO (YAlO₃), YAG (Y₃AI₅O₁₂), rare-earth ultra-phosphates, long afterglow phosphors, starch and organic pigments are evaluated based on temperature dependences of photoluminescence (PL) lifetime and/or PL intensity. Characteristics of these sensor materials are reported for fluorescence thermometer application.

Low temperature fluorescence thermometer application of long afterglow phosphorescent SrAl12O19:Eu2+,Dy3+ crystals

Photoluminescence from long afterglow phosphorescent SrAl12O19:Eu2+,Dy3+ phosphor crystals have been studied for a fluorescence thermometer at a temperature lower than 200K. Broadband emissions peaking at λ=404 and 519nm are observed from the crystals at room temperature. The λ=519nm emission is strongly coupled with hole traps generated by the auxiliary activator, which dominates long afterglow phosphorescence from the crystals. The lifetime of the λ=519nm emission was, therefore, much longer than that at λ=404nm. The intensity of the λ=404nm emission decreases with decreasing temperature and it also decreases with increasing in the intensity of λ=371nm emissions due to P7∕26-S7∕28 transition. The intensity of λ=371nm emissions is found to be extremely sensitive to the temperature below 200K. The peak intensity ratio between λ=371nm emissions and the λ=404nm emission is effective for the highly sensitive measurement of a temperature lower than 200K.

Temperature measurement using fluorescence image

Fluorescence thermometer using photoluminescence (PL) images from sensor is studied for two-dimensional and non-contact temperature measurement. Visible light PL images can be observed clearly from fluorescence thermo-sensors using CCD camera with green, blue and/or UV excitation. Temperature can be measured based on temperature dependence of brightness of the PL images. Video images processing technique is found to be effective for fluorescence temperature measurement based on PL images from the crystal and composite sensors.

Fluorescence Thermometer Based on 2-Dimensional Photoluminescence Imaging

Two-dimensional photoluminescence (PL) image from sensor material is evaluated for fluorescence thermometer application. Two dimensional PL image is observed using CCD video camera under blue and/or UV LED illuminations. Red colored PL image can be observed from ruby sensor under illumination of blue LED. Brightness of red signal of PL image from ruby sensor varies linearly with temperature from 20 to 100degC Temperature can be measured based on brightness of PL images from fluorescence thermo-sensors. Video images processing technique (line scanning of intensity, histogram and integration of signal intensity) is found to be effective for fluorescence temperature measurement using phosphor sensors.

Fluorescence sensor using two-dimensional phosphor array

Two-dimensional sensor array composed of various phosphors has been evaluated for fluorescence thermometer application. In a matrix sensor, 3times3 composite phosphors are separately located on 10times10 mm2 polymer substrate. Long afterglow phosphors, starch and ruby composites are used as phosphor of sensor array. Photoluminescence (PL) from phosphor composites on matrix sensor are evaluated using a fiber spectrometer. Two dimensional observation of PL from matrix sensor is also observed using CCD camera and UV illumination. Images processing technique is found to be effective for two dimensional evaluation of PL from the sensor array.