Dual mode luminescence and abnormal thermal quenching of Ho3+ activated Ca2SnO4 phosphors

In this work, Ho³⁺ and Ho³⁺/Yb³⁺ co-doped Ca₂SnO₄ (CSO) phosphors are synthesized using high-temperature solid-state method. Under 980 nm excitation, CSO: Ho³⁺/Yb³⁺ exhibits 550 nm green emission (⁵F₄, ⁵S₂ → ⁵I₈) and 650 nm red emission (⁵F₅ → ⁵I₈) via a two-photon UC process, and the luminescence chromaticity is independent of the dopant concentration. Intense pure 550 nm green emission with abnormal thermal quenching effect in CSO: Ho³⁺ and CSO: Ho³⁺/Yb³⁺ phosphors are obtained under 461 nm blue excitation. The green emission intensities of CSO: Ho³⁺ and CSO: Ho³⁺/Yb³⁺ reach 106 % at 373 K and 112 % at 348 K, respectively, in comparison to that at ambient temperature (298 K), which is attributed to matrix based intrinsic defects. The incorporation of Yb³⁺ in CSO: Ho³⁺ further enhances the fluorescence intensity from 87.7 % to 103.8 % at 423 K. These phosphors with UC and DC dual-mode luminescence and abnormal thermal quenching behavior have application prospect for green emitting LEDs.