Two-pulse and stimulated nuclear-quadrupole-resonance echoes in YAlO3:Pr3+

Abstract

The dephasing of trivalent praseodymium dilute in yttrium aluminum oxide (${\mathrm{YAlO}}_{3}$) in the ground electronic state $^{3}$${\mathit{H}}_{4}$ state is evaluated using an optically detected method, to measure two-rf-pulse- and three-rf-pulse-stimulated nuclear quadrupole echoes. The magnitude of the echo is obtained by detecting the weak Raman optical field generated by the interaction of the magnetic moment of the echo and a light beam resonant with the $^{3}$${\mathit{H}}_{4}$(0 ${\mathrm{cm}}^{1}$) to $^{1}$${\mathit{D}}_{2}$(16 374 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) optical transition. This same light beam is used as an optical pump (37-ms duration) prior the rf-pulse sequence to increase the population difference of the hyperfine energy levels, thereby improving the echo signal. The light is turned off 9 ms before the rf-pulse sequence and remains off until the echo to avoid optical-pumping effects on the measured nuclear-quadrupole-resonance (NQR) echo lifetime. The dephasing time ${\mathit{T}}_{2}$ from two-pulse nuclear-quadrupole-echo measurement is found to be 366\ifmmode\pm\else\textpm\fi{}29 \ensuremath{\mu}s.Three-pulse-stimulated echoes show a fast decay at short times, followed by a slower (240 ms) decay. The Hu-Hartmann uncorrelated-sudden-jump model was fitted to the data. For the two-pulse echo, the best approximation to the data is obtained using a fluctuating field amplitude \ensuremath{\Delta}${\mathrm{\ensuremath{\omega}}}_{1/2}$=7000 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, and the fluctuation rate W=2100 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. In contrast to this, the three-pulse echo data, measured with a much smaller separation of the first two pulses \ensuremath{\tau}, shows an approximate fit using \ensuremath{\Delta}${\mathrm{\ensuremath{\omega}}}_{1/2}$\ensuremath{\approxeq}60 000 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ (\ensuremath{\tau}40 \ensuremath{\mu}s) and W=12 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for data plotted versus the separation between the second and third rf pulses T for several values of the separation of the first two pulses \ensuremath{\tau}, and \ensuremath{\Delta}${\mathrm{\ensuremath{\omega}}}_{1/2}$=125 000 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and W=20 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for data at three fixed values of T, plotted versus \ensuremath{\tau}. The apparent discrepancy between the two-pulse and the three-pulse fits is attributed to two different dephasing host Al nuclei. The fluctuating fields due to bulk Al are effective in dephasing the Pr moment for \ensuremath{\tau}\ensuremath{\ge}${\mathit{T}}_{2}$, and the frozen-core Al, which surround the ${\mathrm{Pr}}^{3+}$ ion, produce a much larger effective field that fluctuates much more slowly, are the dephasing agent for \ensuremath{\tau}\ensuremath{\ll}${\mathit{T}}_{2}$.