Can changing a semiconductor’s composition help it keep glowing as it warms up?

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The trivalent terbium ion (Tb3+) emits ultra-stable visible light in blue, green, yellow, and red. Terbium-doped semiconductors are candidates for new full-color light sources in next-generation displays, and Tb-doped AlxGa1−xN (AlxGa1−xN:Tb) has attracted particular attention for device applications.

In this experimental materials study, researchers examined the luminescence properties of AlxGa1−xN:Tb grown by organometallic vapor phase epitaxy. At 15 K, they observed emission associated with the 5D4–7FJ transitions (J = 3, 4, 5, 6) in samples with x ≥ 0.03.

Higher aluminum compositions suppressed thermal quenching—the weakening of emission as temperature rises—of the 5D4–7FJ emission. This luminescence was clearly observed at room temperature in AlxGa1−xN:Tb with x ≥ 0.06. The researchers attributed the small thermal quenching to enhanced excitation of Tb3+ ions to the 5D4 level through the 4f–5d transition, not to suppression of energy back-transfer paths in excited Tb3+ ions.

Additional emission from the 5D3–7FJ transitions was observed at 15 K in samples with x ≥ 0.15, but it was not observed at room temperature. The researchers explained this absence by the lower efficiency of excitation to the 5D3 level through the 4f–5d transition at high temperature.

For Al0.15Ga0.85N:Tb, the researchers also demonstrated monochromatic green light using a SiO2/ZrO2 distributed Bragg reflector.