Switching Red to Green Upconversion Emission in Y2O3:Yb,Er Phosphor With La3+ Doping and Exploring Optical Thermometric Applications
Harsha S. Deshmukh, G.G. Muley
Abstract
Abstract The upconversion (UC) phosphors in the series (100- x - y - z )Y 2 O 3 + x La 2 O 3 + y Yb 2 O 3 + z Er 2 O 3 with x =0, 2, 4, 6, 8, and 10; y =3; z =0.1 were prepared by a combustion method to know the effect of La 3+ doping on UC emission wavelengths and their intensities. The UC emission has been studied under the 980 nm (power 166 mW) and 932 nm (variable power) diode laser excitation. The phosphors show the green and red band emission pertaining to Er 3+ ions. It has been observed that with a lower concentration of La 3+ ions (up to 6 mol%), the emission intensity of both bands decreased, with the red band emission remaining dominant. However, as the doping concentration exceeded 6 mol%, the emission intensity of the green band increased significantly, leading to a switch from the red to green band emission at 10 mol% La 3+ doping. The variation in the UC emission intensity with the pump power and temperature has been measured. The Er 3+ and Yb 3+ co-doped UC phosphor with 10 mol% La 3+ doping can be used in optical thermometry with the maximum absolute sensitivity of 0.054 3 K −1 at 303.15 K. The cubic crystal structure of prepared samples has been confirmed by a powder X-ray diffraction study. Doping of La 3+ did not change the crystal structure, but the variation in lattice parameters was witnessed due to the modification of the crystal field by the La 3+ ion. The absorbance of samples over the spectral range of 200 nm–1 100 nm has been measured by the diffuse reflectance spectroscopy. All samples exhibited large band gaps. The morphology of particles has been studied by the scanning electron microscopy. Commission International de I’Eclairage (CIE) color coordinates have been determined.