Orbach Relaxation and Hyperfine Structure in the ExcitedE¯(E2)State ofCr3+inAl2O3

Abstract

Several methods of optical detection of electron paramagnetic resonance (epr) of excited states in crystals are outlined. The application of these methods to observation of epr in the excited metastable $\overline{E}\left({}_{}{}^2{}_{}{}^{}E\right)$ state of ${\mathrm{Cr}}^{3+}$ in ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ is described. The most recent technique made use of a high-resolution optical spectrometer to monitor the change of intensity of one of the Zeeman components of the $R_1$ fluorescent light [$\overline{E}\left({}_{}{}^2{}_{}{}^{}E\right)\to {}_{}{}^4{}_{}{}^{}A_2^{}{}_{}{}^{}$] as $\overline{E}$ was saturated by the microwaves when the magnetic field was swept through resonance. A sample doped with Cr enriched to 92% ${\mathrm{Cr}}^{53}$ was used to study the hfs in the $\overline{E}$ state. An upper limit of 25 kG is set on the hyperfine field per unit spin ($\frac{A}{g_I{\beta }_N}$). This small value compared to that of 200 kG for the ground-state results from a near cancellation of the negative core polarization field by an equally large but positive orbital field. The spin-lattice relaxation time $T_1$ in the $\overline{E}$ level was determined by observing the recovery of the light signal after the microwave saturating pulse was switched off. A continuous averaging technique using a multichannel analyzer was employed to improve the signal-to-noise ratio. $T_1$ is found to very accurately follow an Orbach process with $T_1=3.8\mathrm{}\times {10}^{-9\mathrm{}}{e}^{\frac{\Delta }{\mathrm{kT}}}$ sec where $\Delta =28.8\mathrm{}\pm 1.0$ ${\mathrm{cm}}^{-1\mathrm{}}$, i.e., the separation between $2\overline{A}$ and $\overline{E}$. In the range of temperature where the Orbach process was observed (4.2°K → 2.8°K), $T_1$ was found to be essentially independent of concentration (0.05 and 0.005%) and frequency (24 and 48 kMc/sec), as anticipated. The coefficient 3.8×${10}^{-9\mathrm{}}$ sec is significant in that it measures the maximum transition time from $2\overline{A}$ to

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This publication has 29 references indexed in Scilit:

• Stimulated Optical Emission in Fluorescent Solids. II. Spectroscopy and Stimulated Emission in Ruby
  Physical Review B, 1961
• Paramagnetic Resonance Absorption in Naphthalene in Its Phosphorescent State
  The Journal of Chemical Physics, 1961
• Detection of Double Resonance by Frequency Change: Application toHg201
  Physical Review B, 1961
• Optical and Microwave-Optical Experiments in Ruby
  Physical Review Letters, 1960
• Self-Absorption and Trapping of Sharp-Line Resonance Radiation in Ruby
  Physical Review Letters, 1959
• Absorption Spectra of Cr³⁺ in Al₂O₃ Part B. Experimental Studies of the Zeeman Effect and Other Properties of the Line Spectra
  Journal of the Physics Society Japan, 1958
• Absorption Spectra of Cr³⁺ in Al₂O₃ Part A. Theoretical Studies of the Absorption Bands and Lines
  Journal of the Physics Society Japan, 1958
• Doppelresonanz durch Anregung mit Hyperfeinstrukturkomponenten und Nachweis durch Selbstabsorption
  The European Physical Journal A, 1958
• Eine neue Form der Doppelresonanzmethode
  The Science of Nature, 1956
• A New "Double Resonance" Method for Investigating Atomic Energy Levels. Application toHg P13
  Physical Review B, 1952

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