A crystal of Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{+2}$ masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable $^{5}D_{0}$ level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the $^{5}D_{0}$ level while in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr ${\mathrm{Cl}}_{2}$ : ${\mathrm{Sm}}^{2+}$ were also studied in this regard and display an expected close similarity in spectral characteristics to Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ . The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ and Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ , indicating weaker coupling to the lattice in the excited $5d$ state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of ${\mathrm{Sm}}^{2+}$ ions is given.A crystal of Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{+2}$ masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable $^{5}D_{0}$ level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the $^{5}D_{0}$ level while in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr${\mathrm{Cl}}_{2}$: ${\mathrm{Sm}}^{2+}$ were also studied in this regard and display an expected close similarity in spectral characteristics to Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$. The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ and Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$, indicating weaker coupling to the lattice in the excited $5d$ state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of ${\mathrm{Sm}}^{2+}$ ions is given.

Physical ReviewJul 15, 196266 citations

Two-photon excitation of Ho3+ in the Ca F2 , Sr F2 , and Cd F2 lattices

D. Narayana Rao, Jagdish Prasad, Paras N. Prasad

The observation of two-photon absorption by a very efficient up-converted emission is reported for ${\mathrm{Ho}}^{3+}$ in Ca ${\mathrm{F}}_{2}$ , Sr ${\mathrm{F}}_{2}$ , and Cd ${\mathrm{F}}_{2}$ with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band $A$ is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band $B$ is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for ${\mathrm{Ho}}^{3+}$ in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands $A$ and $B$ arise from two different modes of two-photon excitation. The band $A$ is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band $B$ is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.The observation of two-photon absorption by a very efficient up-converted emission is reported for ${\mathrm{Ho}}^{3+}$ in Ca${\mathrm{F}}_{2}$, Sr${\mathrm{F}}_{2}$, and Cd${\mathrm{F}}_{2}$ with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band $A$ is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band $B$ is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for ${\mathrm{Ho}}^{3+}$ in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands $A$ and $B$ arise from two different modes of two-photon excitation. The band $A$ is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band $B$ is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.

Physical review. B, Condensed matterJul 1, 198322 citations

A crystal of Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{+2}

masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable

^{5}D_{0}

level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the

^{5}D_{0}

level while in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr

{\mathrm{Cl}}_{2}

{\mathrm{Sm}}^{2+}

were also studied in this regard and display an expected close similarity in spectral characteristics to Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

. The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

and Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

, indicating weaker coupling to the lattice in the excited

5d

state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of

{\mathrm{Sm}}^{2+}

ions is given.

The observation of two-photon absorption by a very efficient up-converted emission is reported for

{\mathrm{Ho}}^{3+}

in Ca

{\mathrm{F}}_{2}

, Sr

{\mathrm{F}}_{2}

, and Cd

{\mathrm{F}}_{2}

with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band

A

is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band

B

is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for

{\mathrm{Ho}}^{3+}

in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands

A

and

B

arise from two different modes of two-photon excitation. The band

A

is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band

B

is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.