NaYF₄ : Ho³⁺, Yb³⁺@PEI Upconversion Luminescence Microparticles as Multichannel Optical Sensors for the Identification of Coffee Varieties

The luminescence of beta - NaYF4 : Ho3+, Yb3+@PEI-coffee microparticles suspended in water was studied using three different types of coffee from Peru: the first from Rioja, the second from Cuzco, and the third one from Chanchamayo. The upconversion (UC) emission of these microparticles was studied for emission wavelengths of 542nm, 645nm and 753nm corresponding to F-5(4),S-5(2) -> I-5(8); F-5(5) -> I-5(8) and F-5(4),S-5(2) -> I-5(7) transitions respectively, varying the intensity of the 980nm diode laser used to excite the microparticles. The average relations Avg I-21, Avg I-31, and Avg I-23 of the UC emission intensities were used to identify the different coffee varieties. Avg I-21 = 0.3 for coffee A, and 0.17 for coffees B and C. Avg I-31 = 0.26 for coffee A and 0.17 for coffees B and C. Avg I-23 was used to identify coffee B from coffee C. For coffee, A, Avg I-23 = 1.2 for coffee A,1 for coffee B and 0.9 for coffee C. The UC emission changes in the samples showed that the beta - NaYF4 : Ho3+, Yb3+@PEI microparticles can be used as microsensors in the identification of coffee varieties.