Emission cross section and fluorescence efficiency of Nd-pentaphosphate

The room-temperature cross sections for the Nd
^3+
4
F_{3/2}
levels to the
⁴
I_{11/2}
and
⁴
I_{9/2}
manifolds (lower laser state and ground state, respectively) in NdP
5
O
14
are measured by two spectroscopic methods. A value for the largest cross section of
\sigma(R_{1} - Y_{2}) = 1.7 \times 10^{-19}
cm
²
is found. The highest effective cross section, resulting from superposition of two lines at 1.051 μm, gives a laser gain per Nd ion which is about 2/3 of the maximum gain in YAG:Nd. The relative branching ratio into the
⁴
I_{11/2}
and
⁴
I_{9/2}
manifolds is 0.65:0.35. Comparison of the integrated cross sections with the measured lifetime for 1-percent Nd in LaP
5
O
14
indicates a combined efficiency <0.1 for the remaining transitions, namely radiative decay into the
⁴
I_{13/2}
and
⁴
I_{15/2}
manifolds and multiphonon quenching. A measurement of temperature dependence of fluorescence lifetime supports this last result.