Intense visible upconversion emission in transparent (Ho3+, Er3+)-α-Sialon ceramics under 980 nm laser excitation

A very intense infrared to visible frequency upconversion and near infrared frequency downconversion photoluminescence has been reported for the first time in Ho3+ and Er3+ co-doped transparent α-Sialon ceramics under 980 nm laser excitation. The α-Sialon ceramics were prepared by hot press sintering technique. Distinct upconversion bands at 553 nm, 656 nm, 671 nm and a downconversion band at 1530 nm were assigned to the transitions from 4S3/2 to 4I15/2 (Er3+), 5F5 to 5I8 (Ho3+), 4F9/2 to 4I15/2 (Er3+), and 4I13/2 to 4I15/2 (Er3+) respectively. The results show that there is very efficient energy transfer between Er3+ and Ho3+ ions. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two photon absorption process. The highest phonon energy was found to be 855 cm−1. Excellent up and down conversion emission properties together with moderately low phonon energy of the α-Sialon ceramics make the material potential candidate for multifunctional applications.