Microstructure and optical properties of Pr3+-doped hafnium silicate films

In this study, we report on the evolution of the microstructure and photoluminescence properties of Pr3+-doped hafnium silicate thin films as a function of annealing temperature (TA). The composition and microstructure of the films were characterized by means of Rutherford backscattering spectrometry, spectroscopic ellipsometry, Fourier transform infrared absorption, and X-ray diffraction, while the emission properties have been studied by means of photoluminescence (PL) and PL excitation (PLE) spectroscopies. It was observed that a post-annealing treatment favors the phase separation in hafnium silicate matrix being more evident at 950°C. The HfO2 phase demonstrates a pronounced crystallization in tetragonal phase upon 950°C annealing. Pr3+ emission appeared at TA = 950°C, and the highest efficiency of Pr3+ ion emission was detected upon a thermal treatment at 1,000°C. Analysis of the PLE spectra reveals an efficient energy transfer from matrix defects towards Pr3+ ions. It is considered that oxygen vacancies act as effective Pr3+ sensitizer. Finally, a PL study of undoped HfO2 and HfSiOx matrices is performed to evidence the energy transfer.