The purpose of this research program was to create and study novel luminescence particles (phosphors} capable of sensing and retaining the time-temperature information to which they were exposed, therefore acting as nano- and microsized thermosensors. The thermometric property is the latent thermoluminescence (TL) signal associated with electron/hole pairs trapped at defect energy levels, which are differently affected by the environmental temperature.

Conceptual diagram of the primary thrust of the proposed luminescent particle research, including development of luminescent materials, determination of algorithms to extract thermal history, and experimental testing of both materials and algorithms under temperature profiles typical of agent defeat events.

The Defense Threat Reduction Agency (DTRA) mission of combating WMD includes the research and development of Agent Defeat Weapons (ADW) capable of destroying chemical and biological agent facilities and stockpiles with minimum collateral damage, particularly avoiding the dispersion of viable agents to the environment. High-temperature produced by slow-burning incendiary materials is one of the kill mechanisms investigated to neutralize different types of agents, including dry spores, vegetative cells, viruses, toxins and chemical agents. One of the obstacles on advancing the research on new types of energetic materials and mechanisms of biological agent neutralization, however, is the inability of current technology to measure the entire time-temperature profile of very small particles in extreme conditions.

The TL technique investigated in this study has the potential to record the entire temperature history during an agent-defeat test (ADT). Traditional contact (thermocouples, thermistors, etc.) and non- contact temperature measurement methods (spectroscopy, pyrometry) are not capable of determining the temperature experienced by a particle during an ADT. Other techniques under development, such as fluorescence nanoparticle probes, are also not applicable, because they rely on real-time changes in the fluorescence as a function of temperature, and therefore cannot be used in extreme environments (inside blast and fireball, or in dark, smoky blast cloud and dust plume).

The objective of this project was to create and study novel luminescence particles capable of sensing and retaining the time-temperature information to which they were exposed in their thermoluminescence (TL) curves, therefore acting as nano- to microsized thermosensors.

Specific aims of the project were:

To understand the fundamental aspects of the TL mechanism in luminescent particles, learning how to engineer the TL properties during synthesis to develop suitable thermosensors, and create core-shell TL nanostructures capable of distinguishing fast radiative heating from slower convective processes;

To develop and test a multiparametric procedure to extract the critical portions of the temperature profile including heating, maximum temperature, and cooling and to differentiate between fast radiative and slower convection effects based on the TL from single-material and core-shell nanoparticles;

To understand how complicating factors such as pressure and ultraviolet radiation during the explosive process will impact the TL and thermometric properties of the phosphors and, if necessary, how to correct for them.

To achieve these objectives, commercial candidate materials for use as temperature sensors were investigated, and a systematic study was performed to synthesize and develop new materials by looking at various host/dopant combinations. The study also included the development of TL core/shell nanophosphors.

This work was done by Eduardo G. Yukihara, Oklahoma State University; Joseph J. Talghader, University of Minnesota; John Ballato, Clemson University; Luiz G. Jacobsohn, Clemson University, for the Defense Threat Reduction Agency. DTRA-0006


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Luminescence Materials as Nanoparticle Thermal Sensors

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