Dual-ion substituted (MeY)3(AlSi)5O12:Eu garnet phosphors: combinatorial screening, reductive annealing, and luminescence property

Abstract

In recent years, the efficiency of combinatorial methods has been utilized to accelerate the finding or screening of inorganic materials. In this work, based on the double substitution strategy of the cation ions Me²⁺/Si⁴⁺, a series of Me_yY_3−yAl_5−ySi_yO₁₂:Eu_x garnet phosphors (MeYASG:Eu, Me = Mg, Ca, Sr, Ba) were rapidly prepared and screened by a combinatorial method in microreactor arrays. Through parallel experiments of solid-state synthesis, the reliability of the combinatorial screening was verified and an optimal composition of CaY₂Al₄SiO₁₂:Eu_0.03 (CYASG:Eu) with advanced luminous intensity was obtained. Annealing experiments under air and reductive atmospheres were performed and demonstrated the controllability and reversibility of the Eu³⁺ ↔ Eu²⁺ valence transition process, thus realizing the tuning of the dominant emission from divalent Eu²⁺ or trivalent Eu³⁺. The optimal CYASG:Eu sample showed excellent thermal quenching resistance after annealing at 800 °C for 1 h in a reducing atmosphere. The abnormal intensity of PL increased by 10% in the 50–100 °C region, and retained 63% of the initial value at 250 °C. With the assistance of thermoluminescence characterization, the complementary effect of the release of captured electrons or charge carriers in trap levels on the abnormal increase of PL intensity during the high-temperature luminescence process was revealed. By combination of the double substitution strategy of cations and annealing, a new approach is proposed to creating the coexistence of activator Eu ions with a mixed-valence state. Also, the prepared CYASG:Eu phosphors have promising applications in fields such as plant light supplements in greenhouses and plant factories and as luminescent materials for energy-saving light sources.