Sm3+ doped novel Sr3In2Ge3O12 orange-red emitting phosphor for WLEDs with high color purity and color rendering index

To address the limitations of conventional white light emitting diodes (WLEDs), such as insufficient red light components and low color rendering index (R_a), a series of Sm³⁺ doped germanate orange red phosphors Sr_3-xIn₂Ge₃O₁₂:xSm³⁺ (0 ≤ x ≤ 0.14) were synthesized via high-temperature solid-state reaction in this study. The systematic characterizations of their structure and optical properties were performed. The results indicate that all samples belong to the cubic crystal system with space group Ia-3d, where Sm³⁺ successfully occupies the [SrO₈] polyhedral sites. XRD refinement and EDS analysis indicate the formation of the target phase Sr₃In₂Ge₃O₁₂:Sm³⁺, with the presence of a small amount of impurity phase. Upon excitation with 404 nm near-ultraviolet light, the germanate phosphors exhibited a characteristic orange red emission at 563 nm, attributing to the ⁴G_5/2→⁶H_5/2 transition of Sm³⁺. The optimal doping concentration was determined to be x = 0.1, yielding CIE 1931 coordinates of (0.506, 0.491) in the orange-red region with 94.2% color purity. The concentration quenching mechanism is electric dipole-dipole interaction with the critical distance R_c = 17.2 Å. The Sr_2.9In₂Ge₃O₁₂:0.1Sm³⁺ exhibits millisecond-level photoluminescence (PL) lifetime and excellent thermal stability, retaining 69% of its room-temperature PL intensity at 250 ℃. WLEDs assembled with this as the orange-red component demonstrate stable electroluminescence (EL), retaining 82% of initial EL intensity after 12 hours of continuous operation, with the R_a as high as 90. This study leverages the rigid framework and high ionic compatibility of the germanate host to achieve both high color purity and excellent thermal stability, providing a novel orange red candidate material for high-color-rendering WLEDs.