Thermal and size effect on the R lines luminescence in YAG:Cr³⁺

We have studied the line positions and widths of R lines luminescence of nanopowder samples of Y₃Al₅O₁₂: Cr ³⁺ particles with diameters ranging from about 28 to 250 nm. For each sample we have measured accurately the emission spectrum from 30 K to 300 K. The spectra generally consisted of the R-lines narrow spectral emission and of the accompanying vibronic side-bands. From larger to shorter diameters of powders at each temperature we noticed an increase of the width at half-maxima of the R lines luminescence. The emissions were shifted towards lower energies when increasing the temperature from 30 K to 300 K. The temperature dependent broadening and shift of the R lines in the different samples can be accounted for by adjusting the electron-phonon parameters in the formulas describing these processes and using the same Debye temperature of the bulk material.