  Lead halide perovskite nanocrystals (NCs) in a glass matrix combine excellent
optical properties and stability against environment. The spectral and temporal
characteristics of photoluminescence from CsPbBr$_3$ and CsPb(Cl,Br)$_3$
nanocrystals (NCs) in a fluorophosphate glass matrix are measured in a
temperature range from 6 to 270 K in order to reveal factors that determine
their quantum yield and recombination dynamics. At low temperatures, the
recombination dynamics is characterized by three decay components with time
scales on the order of 1 ns, 10 ns, and 1 $\mu$s. The relative contributions of
the corresponding processes and their characteristic times are strongly
temperature dependent. The emission intensity decreases with growing
temperature. This effect is stronger in smaller NCs, which highlights the role
of surface states. These experimental results are discussed on the basis of a
model taking into account the NC energy structure and the presence of electron
and hole surface trap states. The photoluminescence dynamics at low
temperatures is dominated by charge-carrier radiative recombination and
relaxation to shallow traps. At temperatures exceeding 100 K, the dynamics is
affected by carrier activation to the excited states.
