EN
Luminescence decay curves for the ^{4}G_{5/2} → ^{6}H_{7/2} emission of Sm^{3+} in the cubic hexachloroelpasolite crystals Cs_{2}NaSm_{x}Y_{1-x}Cl_{6} (x=0.005 to x=1) and Cs_{2}NaSm_{x}Eu_{y}Y_{1-x-y}Cl_{6} (x=0.01 to x=0.95, y=0.05 to y =0.99) have been measured over the temperature range 10 K to 300 K using pulsed laser excitation into the ^{4}G_{5/2} state of Sm^{3+}. The luminescence from this state is strongly quenched by cross relaxation to Sm^{3+} acceptors and energy transfer to the ^{5}D_{0} state of Eu^{3+}. The temperature dependence of cross relaxation and of energy transfer is discussed in terms of the involved mechanisms.