EN
The luminescence decay curves from the ^{4}F_{9/2} and ^{4}I_{9/2} states of the cubic hexachloroelpasolite crystals Cs_{2}NaEr_{x}Y_{1-x}Cl_{6} (x = 0.001÷1) have been measured over the temperature range 10-300 K. The ^{4}I_{9/2} state undergoes an electric dipole vibronic-electric dipole vibronic cross-relaxation process at 300 K, but this mechanism is inefficient below 165 K. Excitation into the ^{4}F_{9/2} state, results in emission in the green, blue and ultra violet regions. The up-conversion processes which could account for the ultraviolet emission are discussed.