Change of the luminescence decay time for Lu$_2$O$_3$ : Eu nanocrystals embedded in synthetic opal

The opal-Lu$_{1.86}$Eu$_{0.14}$O$_3$ composites have been prepared using the developed technique for synthesizing luminophor nanocrystals in pores of synthetic opal through coprecipitation from a solution. It has been demonstrated that the position of the photonic stop band in the reflection spectrum of the infiltrated opal depends on the diameter of its spheres, the volume fraction of the embedded luminophor, and the angle of detection of the signal. The excitation and photoluminescence spectra of the composites have been analyzed, and the lifetime of the $^5D_0$ excited state of Eu$^{3+}$ ions has been examined. It has been revealed that the luminescence decay time for the luminophor increases by almost one order of magnitude with an increase in its content in opal pores. This effect has been attributed to the change in the nanocrystal size and to the decrease in the contribution from the surface nonradiative recombination in luminophor nanolayers of the composites.