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The luminescent lifetime of La 2 Zr 2 O 7 and La 2 Hf 2 O 7 has been determined as a function of temperature. We have shown that the luminescence of both materials can be used to determine the temperature of a surface up to 1073 K. The results are qualitatively explained via multiphonon emission. Phonon energies and the number of phonons needed to cross the energy gap are estimated. The results are useful in the design of phosphors for noncontact thermometry in high-temperature applications.

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The luminescent lifetime of cerium-doped yttrium aluminum garnet has been determined as a function of temperature and as a function of gallium content. We have shown that increasing gallium content decreases the decay lifetime and results in luminescence quenching at lower temperatures. The results are quantitatively explained using a configurational coordinate diagram.

Purpose: Current KCl:Eu 2+ prototype dosimeters require a wait time of 12 h between irradiation and dosimetric readout. Although irradiating the dosimeters in the evening and reading on the following day works well in the clinical schedule, reducing the wait time to few hours is desirable. The purposes of this work are to determine the origin of the unstable charge-storage centers and to determine if these centers respond to optical or thermal excitation prior to dosimetric readout. Methods: Pellet-style KCl:Eu 2+ dosimeters were fabricated in-house for this study. A 6 MV photon beam was used to irradiate the dosimeters. After x ray irradiation, dosimeters were subjected to external excitation with near-infrared (NIR) light, ultraviolet (UV) light, or thermal treatment. Photostimulated luminescence (PSL) signal's temporal stability was subsequently measured at room temperature over a few hours using a laboratory PSL readout system. The dosimeters were also placed in a cryostat to measure the temperature dependence of the temporal stability down to 10 K. Results: Strong F-band was present in the PSL stimulation spectrum, indicating that F-centers were the electron-storage centers in KCl:Eu 2+ where an electron was stored at a chlorine anion vacancy. Due to deep energy-depth (2.2 eV), F-centers were probably not responsible for the fast fading in the first a few hours post x ray irradiation. In addition, weak NIR bands were present. However, there was no change in PSL stabilization rate with intense NIR excitation, suggesting that the NIR bands played no role in the PSL fading. At temperatures lower than 77 K there was almost no signal fading with time. Noticeable PSL was observed for undoped KCl samples at room temperature, suggesting that Cl 2 − V k centers served as hole-storage centers for both undoped and doped KCl where a hole was trapped by a chlorine molecular ion. V k centers were stable at low temperature and became mobile at room temperature, probably causing the observed PSL fading with time. On the other hand, V k center could be stabilized by Eu 2+ activator or oxygen in the lattice, leading to the stable component in the PSL. A thermal process at elevated temperatures (60• C or higher) was able to significantly accelerate the migration process resulting in a fast stabilization of PSL. However, this could not be accomplished using intense UV excitation. Conclusions: Thermal treatment enables KCl:Eu 2+ prototypes to be ready for readout in 1 h without the need of applying a large time-dependent correction factor. However, this cannot be achieved using optical preexcitation.

The decay time of the phosphor YAG:Ce is temperature dependent. Selective incorporation of gallium into the YAG:Ce matrix permits tuning the temperature at which quenching begins. Also, the size of the phosphor particle and processing method affect this characteristic. We describe one such situation in which quenching of the combustion synthesized nanophosphor Y 3 (Al 0.5 Ga 0.5) 5 O 12 :Ce 1% was observed from ambient to 125 C. By signal averaging of laser excited fluorescence, temperature uncertainties ranged from 0.05 to 0.15 C. The single shot temperature uncertainty at 115 C was ± 3 C, indicating the feasibility for transient thermometry with response rate exceeding 1 MHz.

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Recent research has demonstrated that europium doped potassium chloride (KCl:Eu2+) storage phosphor material has the potential to become the physical foundation of a novel and reusable dosimetry system using either film-like devices or devices similar to thermoluminescent dosimeter (TLD) chips. The purposes of this work are to quantify the performance of KCl:Eu2+ prototype dosimeters for low dose measurements and to demonstrate how it can be incorporated into clinical application for in vivo peripheral dose measurements. Pellet-style KCl:Eu2+ dosimeters, 6 mm in diameter, and 1 mm thick, were fabricated in-house for this study. The dosimeters were read using a laboratory photostimulated luminescence detection system. KCl:Eu2+ prototype storage phosphor dosimeter was capable of measuring a dose-to-water as low as 0.01 cGy from a 6 MV photon beam with a signal-to-noise ratio greater than 6. A pre-readout thermal annealing procedure enabled the dosimeter to be read within an hour post irradiation. After receiving large accumulated doses (~10 kGy), the dosimeters retained linear response in the low dose region with only a 20 percent loss of sensitivity comparing to a fresh sample (zero Gy history). The energy-dependence encountered during low dose peripheral measurements could be accounted for via a single point outside-field calibration per each beam quality. With further development the KCl:Eu2+− based dosimeter could become a versatile and durable dosimetry tool with large dynamic range (sub-cGy to 100 Gy).