Enhanced 1.5 μm emission of Er3+-doped multifunctional Bi2ZnOB2O6 microcrystals
The efficiency of the 1.5 μm emission associated with the 4I13/2 → 4I15/2 transition of Er3+ ions of a series of Er3+ and Yb3+/Er3+-doped Bi2ZnOB2O6 microcrystalline powders was investigated. Bi2ZnOB2O6 is an excellent nonlinear optical material as well as a good host matrix for luminescent rare-earth ions. The investigated powders were synthesized by means of the modified Pechini method and their orthorhombic structure with Pba2 space group were confirmed by XRD measurements. The vibrational properties of Bi2ZnOB2O6:Yb3+/Er3+ were studied using μ-Raman spectroscopy. The low phonon energy of the Bi2ZnOB2O6 matrix allows effective phonon assisted energy transfer between rare-earth ions and/or multiphonon relaxation processes of rare-earth ions. It was revealed that the intensity of the 1.5 μm emission under 980 nm excitation increased with increasing Er3+ concentration (from 0.5 to 3.0 at%) for Bi2ZnOB2O6:Er3+, while for co-doped Bi2ZnOB2O6:Yb3+/Er3+ systems a significant increase in this emission was observed for the optimal Yb3+/Er3+ concentration (1.5/0.5 at%). Moreover, the intensity of the 1.5 μm emission decreases with increasing temperature for all investigated samples. Additionally, Bi2ZnOB2O6:Yb3+/Er3+ powders exhibit effective up-conversion luminescence in the visible range under 980 nm excitation. In the up-conversion spectra of Bi2ZnOB2O6:Yb3+/Er3+ powders, the bands corresponding to green and red emission of Er3+ ions (2H11/2 → 4I15/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively), as well as the bands at about 487 nm (blue emission) associated with second harmonic generation produced by the Bi2ZnOB2O6 matrix were detected. The results indicate a potential for application of Bi2ZnOB2O6:Yb3+/Er3+ powders as effective multifunctional new-generation photonic materials.