Site occupancy and photoluminescence properties of a novel deep-red-emitting phosphor NaMgGdTeO6:Mn4+ with perovskite structure for w-LEDs

Abstract

A novel kind of deep red-emitting phosphor NaMgGdTeO6:Mn4+ prepared by a high-temperature solid-state reaction method is reported in this article. Rietveld refinement for the representative NaMgGdTeO6 host showed that its crystal structure is isostructural with that of the NaMgLaTeO6 compound. XRD measurements for the representative samples indicated a pure phase for the as-prepared phosphors and the successful introduction of Mn4+ into this matrix. Under UV or blue excitation, the NaMgGdTeO6:0.01Mn4+ shows a narrow emission band ranging from 12,500 cm−1 (800 nm) to 16,667 cm−1 (606 nm) centered at 14,347 cm−1 (697 nm), which has been attributed to the Mn4+ spin and parity-forbidden transition 2Eg→4A2g. Monitored at 697 nm, the phosphor exhibits a wide excitation band from 40,000 cm−1 (250 nm) to 16,667 cm−1 (600 nm) with four Gaussian peaks at 31,546 cm−1 (317 nm), 28,329 cm−1 (353 nm), 24,630 cm-1 (406 nm), and 20,833 cm-1 (480 nm), corresponding to the O2-→Mn4+ charge-transfer transition and the Mn4+ spin-allowed transitions 4A2g→4T1g, 4A2g→2T2g and 4A2g→4T2g, respectively, which can match well with commercial UV and blue chips. The optimal Mn4+-doping percentage for this phosphor was determined to be NaMgGdTeO6:0.01Mn4+ with a quantum yield of 41.19% upon 365 nm excitation. Concentration quenching took place with further Mn4+-concentration increase in NaMgGdTeO6:Mn4+, where the energy transfer mechanism was analyzed to be an electronic dipole-dipole interaction. Moreover, the luminescent decay times monitored at 697 nm showed a reasonable decrease with increasing Mn4+ concentration. The time-resolved emission spectra and decay times monitored at 680 and 720 nm of NaMgGdTeO6:0.01Mn4+ led to the distinguishing of two kinds of Mn4+ sites in the crystal structure. In addition, the temperature-dependent luminescence properties illustrated a good luminescence thermal stability. These results suggest that this kind of phosphor can be considered as a supplement of the red component for w-LEDs.