We investigate the luminescent spectrum of thin films of dye molecules embedded in a polymer layer and on top of an array of aluminum nanoparticles. The emission couples to quasi-guided modes that are efficiently coupled out to free space by scattering with the particle array. This outcoupling provides a significant enhancement of the emission in defined directions. The mode density changes and the spectrum is modified by varying the thickness of the layer. In consequence, the luminous efficacy of the layer of dye can be controlled by the layer thickness and the characteristics of the particle array. This system can be regarded as a luminescent metamaterial with designed properties that can be exploited in solid state lighting applications.