Spectroscopy and upconversion mechanisms ofCsCdBr3:Dy3+

The upconversion luminescence of a ${\mathrm{Dy}}^{3+}$-doped system is presented and analyzed. ${\mathrm{CsCdBr}}_3:x\%$ ${\mathrm{Dy}}^{3+}$ ($x=0.2,$1,5) was synthesized and grown as crystals using the Bridgman technique. ${\mathrm{Dy}}^{3+}$ ions preferentially enter this host as charge-compensated dimers. Due to the low-phonon energy the efficiency of multiphonon-relaxation processes is significantly reduced in this host compared to oxides and fluorides. Yellow-green upconversion luminescence originating from ${}^4{F}_{9/2}$ can be induced upon excitation into ${}^6{F}_{5/2}$ or ${}^6{F}_{3/2}$ in the near infrared (NIR). Depending on the excitation wavelength, upconversion occurs by an energy-transfer or excited-state absorption mechanism. The two are distinguished by their temporal behavior after an excitation pulse. Analysis of the upconversion-luminescence transient of ${\mathrm{CsCdBr}}_3:0.2\%$ ${\mathrm{Dy}}^{3+}$ at 10 K leads to a rate constant $W_t=165\mathrm{}{\mathrm{s}}^{\mathrm{-}1}$ for the energy-transfer step. This is very small, and thus upconversion based on one excitation wavelength is inefficient. In addition, the intermediate NIR level ${}^6{F}_{5/2}$ is significantly depopulated by multiphonon relaxation at room temperature.