Optical Characterization of the Ho$^{3+}$ Complex in HEMA

The spectroscopic properties of the Ho$^{3+}$ complex embedded in 2-hydroxyethyl methacrylate (HEMA) are investigated. The intensities of the room temperature absorption spectra of the Ho$^{3+}$(4$f^{10})$ transitions in Ho(NO$_{3})_{3}$.5H$_{2}$O:HEMA have been analyzed using the Judd-Ofelt (J-O) model to obtain the phenomenological intensity parameters, $\Omega_{2}$, $\Omega_{4}$, and $\Omega_{6.}$ These parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Ho$^{3+}$ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds of $^{2S+1}L_{J}$ Ho$^{3+}$(4$f^{10})$, which include $^{5}$G$_{4}+^{3}$K$_{7}^{(2)}$, $^{5}$G$_{5}$, $^{5}$G$_{6}+^{5}$F$_{1}$, $^{5}$F$_{2}+^{3}$K$_{8}^{(2)}$, $^{5}$F$_{3}$, $^{5}$F$_{4}+^{5}$S$_{2}$, and $^{5}$F$_{5.}$ The predicted room temperature fluorescence lifetime of $^{5}$I$_{7}$ to $^{5}$I$_{8}$ is about 0.5 ms, suggesting a reasonably strong interaction between the complex and the polymer. A comparative study of Ho$^{3+}$(4$f^{10})$ ions in different host materials suggests that Ho(NO$_{3})_{3}$.5H$_{2}$O:HEMA could be an excellent candidate for certain applications such as narrow band pass filters, especially in the visible-to-near infrared region of the spectrum.