In this work, after the synthesis of chlorophosphate- based host glasses doped with Yb ion as active ion, their optical properties such as absorption and emission spectra and thermal properties including transition and crystallization temperature were investigated. By using the DSC analysis indicating the temperatures 500 C as Tg and 800 C as Tc, the suitable annealing temperature was determined at 650 C and then the annealing of the obtained glasses was done to convert them to glass– ceramics. During this heat treatment, NaCl and CaCl2 nanocrystals were grown in the glass matrix and active ions are trapped into this medium. Also, the structural features were analyzed using XRD and SEM and then the size of nanocrystals was obtained from Scherrer’s formula and was evaluated in average 37 nm for 1 %Yb:G–C and 54 nm for 0.5 %Yb:G–C samples. Finally, the absorption and emission spectra of the samples were recorded and analyzed, indicating that the conversion of glasses to glass– ceramics by heat treatment resulted in enhancement of emission intensity about 17 times; so, these glass–ceramics are applicable in frequency converters, solid state lasers and optical devices
