Carboxymethyl cellulose (CMC) are very important derivatives of cellulose, because they have good solubility, high chemical stability, and are toxicologically innocuous. CMC is also one of the important “antenna” ligands. Europium (Eu(Ⅲ)) complexes are unique and attractive because among other benefits, they possess the advantages of a large Stokes shift, narrow red light emissions and long fluorescence lifetimes pH value has big impact on the size and distribution, surface area, microstructure of carboxylate material particles, and then influence their electrochemical and photoelectric properties. So, pH value is an important factor in the synthetic of CMC and Eu3+ ion. In this paper, Eu/CMC was synthesized and the relationships between particle size and distribution and photoluminescence properties were investigated. The result showed that as light conversion materials, CMC firstly absorbs ultraviolet light, and then the absorbed energy is transferred from the lowest triplet state energy level of the CMC to the resonance level of europium ions (Förster resonance energy transfer (FRET)) and makes them send out their characteristic light (see Fig. 1a). FT-IR results confirmed that, on CMC chains, carboxyl groups and the oxygen atom of unsubstituted hydroxyl groups and ether bonds were all involved in the reaction with Eu3+. TG analysis (see Fig.2) showed that CMC/Eu complexes were thermally stable in a wide temperature range from 30 to 300℃. The emission intensity decreased when the pH value increased from 7.0 to 12.0. However, at pH=12, because that the extent of reaction of Eu3+ and CMC decreased and CMC degraded, the complexes had a weak fluorescence intensity. Acknowledgment: We gratefully acknowledge the financial support provided by the National Natural Foundation of China (project 31270617) and State Key