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In this paper, the optical fiber ammonia sensor based on porous Yb 3+ /Er 3+  co-doped NaYF 4  up-conversion material/phenol red composites and optical fiber with end plane fusion sphere was proposed. Phenol red and Yb 3+ /Er 3+  co-doped NaYF 4  were mixed thoroughly and fixed stably in the polyvinylidene fluoride (PVDF) matrix. The optical fiber with end plane fusion sphere was inserted into the sensitive composite material to form ammonia sensitive probe. The ammonia concentration will affect the intensity of absorption of up-conversion luminescence located at 545 nm by phenol red because of the reaction between ammonia and phenol red. The detected intensity of up-conversion luminescence near 545 nm decreases with the increasing ammonia concentration. The signal wavelength will not be affected by the background visible light due to the 980 nm wavelength of excitation is far from the signal wavelength. The response time and recover time also were measured and discussed.

Optical fiber ammonia sensor based on porous Yb 3+ /Er 3+ co-doped NaYF 4 /phenol red composites