Multiphonon relaxation rate from pumped level to upper laser level in YAG:Nd

The rise time of the near-infrared fluorescence intensity has been measured in YAG:Nd³⁺ at room temperature under the excitation by 10 ns duration pulses at 514.5 nm using a time-correlated single photon counting method. The result reveals that the relaxation rate from the pumped level (${}^2\text{K}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ + ${}^2\text{G}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ + ${}^4\text{G}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}$ to the upper level laser level $\text{(}{}^4\text{F}{}_{\mathrm{<mtext>sol3</mtext><mtext>2</mtext>}}\text{)}$ is larger than 10⁸s^?1, which is in contrast with the previously reported values of (1.6 ～ 2) × 10⁶s^?1. An experiment to search for the visible emission in YAG:Nd³⁺ gives support to the present value.