Structural and spectroscopic investigation of Pr3+-doped alumina-silicate oxyfluoride glasses

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Abstract
Pr3+-doped oxyfluoride glasses with composition 45(1-x) SiO2-25 Al2O3-20 Na2CO3-10 CaF2-x Pr2O3 were synthesized by the conventional melt-quenching technique and systematically investigated in terms of their structural, spectroscopic and upconversion properties. The prepared glasses exhibited high optical quality and excellent transparency, reaching approximately 90% transmittance in the visible spectral range. The optical band gap of the undoped glass was determined to be 4.78 eV. Photoluminescence studies revealed characteristic Pr3+ emissions originating from the 3P0 and 1D2 excited states. The strongest luminescence was observed for the sample containing 0.1 mol% Pr3+, whereas increasing dopant concentration resulted in progressive concentration quenching. Excitation spectra demonstrated efficient absorption in the blue spectral region, indicating the suitability of these materials for excitation by commercially available blue laser diodes and LEDs. Time-resolved measurements revealed significantly stronger concentration- and temperature-induced quenching of the 1D2 level compared with the 3P0 state, whose decay dynamics remained nearly temperature independent. A remarkable feature of the developed glasses is their ability to convert blue light into ultraviolet radiation. Upon 444 nm excitation, ultraviolet upconversion emission in the 250–310 nm range, assigned to 5d1→4f2 transitions of Pr3+ ions, was observed. Analysis of the pump-power dependence yielded a slope of 1.7, indicating a two-photon upconversion process involving the 1D2 level as an intermediate state. The coexistence of intense visible downconversion and efficient UV upconversion within a single amorphous host demonstrates the unique multifunctionality of the investigated materials. These findings identify Pr3+-doped oxyfluoride glasses as promising candidates for spectral conversion systems, remote phosphors and advanced photonic devices operating across a broad spectral range.

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