Yuwaraj K. Kshetri

Visible and near-infrared upconversion in α-sialon ceramics

α-Sialon ceramics are well known for highly stressed structural engineering applications owing to their inherently outstanding mechanical and thermo-chemical stability. However, the possibilities of the functional applications such as frequency upconversion in α-sialon ceramics have been scarcely investigated. Here, very intense visible and near-infrared frequency upconversion as well as frequency downconversion emissions are reported for the first time in Er3+, Ho3+, and Tm3+ triply doped α-sialon ceramics under 980 nm excitation. α-Sialon ceramics are prepared using a hot press sintering technique. Efficient energy transfer processes between the dopant ions are found to be responsible for the observed emissions. The upconversion process is governed by a two-photon absorption process. The energy transfer efficiency in the triply doped system is 95.8% while that in Er3+/Ho3+ and Er3+/Tm3+ systems is 71.6% and 66.3%, respectively. Triple doping results in the combination of the emission properties found in the co-doped Er3+/Ho3+ and Er3+/Tm3+ systems and it also reveals a cooperative emission behavior which is not possible with only two dopants. These findings open up the possibility of potential application of the Er3+/Ho3+/Tm3+ doped α-sialon ceramic as an optical material in which efficient luminescent properties can co-exist along with the excellent mechanical and thermo-chemical stability.

Microwave hydrothermal synthesis and upconversion properties of Yb3+/Er3+ doped YVO4 nanoparticles

Yb3+ and Er3+ doped YVO4 (Yb3+/Er3+:YVO4) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb3+/Er3+:YVO4 nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to 2H11/2, 4S3/2 to 4I15/2 and 4F9/2 to 4I15/2 transitions of Er3+ respectively. The emission intensity is found to depend strongly on the concentration of Yb3+. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.