Study of phonon-induced energy transfer processes in crystals using heat pulses

Technical Report · Wed Mar 01 04:00:00 EST 1978

DOI:https://doi.org/10.2172/7032870· OSTI ID:7032870

Burns, A R

The artificial generation of acoustic lattice vibrations by a heat pulse technique is developed in order to probe phonon interactions in molecular crystals. Specifically, the phonon-assisted delocalization of ''trapped'' excited triplet state energy in the aromatic crystal 1,2,4,5-tetrachlorobenzene (TCB) is studied in a quantitative manner by monitoring the time-resolved decrease in trap phosphorescence intensity due to the propagation of a well-defined heat pulse. The excitation distribution in a single trap system, such as the X-trap in neat h/sub 2/-TCB, is discussed in terms of the energy partition function relating the temperature dependence of the trap phosphorescence intensity to the trap depth, exciton bandwidth, and the number of exciton band states. In a multiple trap system, such as the hd and h/sub 2/ isotopic traps in d/sub 2/-TCB, the excitation distribution is distinctly non-Boltzmann; yet it may be discussed in terms of a preferential energy transfer between the two trap states via the exciton band. For both trap systems, a previously developed kinetic model is presented which relates the efficiency of trap-band energy exchange to the density of band states and the trap-phonon coupling matrix elements. A bolometric technique for determining the thermal response time of the heater/crystal system is presented. The phonon mean free path in the crystal is size-limited, and the heater/crystal boundary conductance is reasonably close to previously reported values. The theory of heat pulse phonon spectroscopy is presented and discussed in terms of black-body phonon radiation.

• Research Organization: California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7032870
• Report Number(s): LBL-7631
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
AROMATICS
CHLORINATED AROMATIC HYDROCARBONS
CRYSTALS
ENERGY DEPENDENCE
ENERGY TRANSFER
HALOGENATED AROMATIC HYDROCARBONS
HEAT TRANSFER
LATTICE VIBRATIONS
LUMINESCENCE
MOLECULAR CRYSTALS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PHONONS
PHOSPHORESCENCE
PHYSICAL PROPERTIES
QUASI PARTICLES
SPECIFIC HEAT
THERMODYNAMIC PROPERTIES
TRAPS