Super luminescence enhancement, luminescence color-changing and emission mechanism of Sr1.5Ca0.5Al2SiO7:aCe4+,bTb3+

Abstract

In this work, we successfully synthesized Ce⁴⁺-doped, Tb³⁺-doped, and Ce⁴⁺/Tb³⁺ co-doped Sr_1.5Ca_0.5Al₂SiO₇ (SCASO) using the high-temperature solid-state method under atmospheric conditions. Our experimental results reveal that SCASO:aCe⁴⁺ exhibits strong violet-blue luminescence at 392 nm when excited at 338 nm. For SCASO:bTb³⁺, the optimal excitation and emission wavelengths are 371 nm and 538 nm, respectively, with a lower emission intensity and a yellow-green visual color. Both SCASO:aCe⁴⁺ and SCASO:bTb³⁺ achieve optimal sintering at 1400 °C, with doping concentrations of a = 0.01 and b = 0.08. Different from the common internal transition luminescence of Ce³⁺, there is an efficient energy transfer between Ce⁴⁺ and Tb³⁺ in the Ce⁴⁺/Tb³⁺ co-doped SCASO system (SCASO:aCe⁴⁺,bTb³⁺) due to the existence of the Ce⁴⁺–O²⁻ charge transfer band. At 338 nm excitation, the Tb³⁺ emission showed a super enhancement effect with a maximum enhancement of 1813.6%, breaking the limit of no more than 10-fold enhancement of FRET. Moreover, by adjusting the a and b values in SCASO:aCe⁴⁺,bTb³⁺, the emission color of the samples can be continuously tuned from violet-blue to yellow-green. Additionally, SCASO:aCe⁴⁺ and SCASO:aCe⁴⁺,bTb³⁺ demonstrate long afterglow emission lasting over one hour, attributed to the trapping levels in the SCASO host's defect energy levels, a property absent in SCASO:bTb³⁺. Based on these experimental results, we provide a comprehensive and reasonable theoretical interpretation of the luminescence mechanisms for SCASO:aCe⁴⁺ and SCASO:bTb³⁺, the super-enhanced Tb³⁺ emission in SCASO:aCe⁴⁺,bTb³⁺, and the long-afterglow emission process.