Chromium Cluster Luminescence: Advancing Near‐Infrared Light‐Emitting Diode Design for Next‐Generation Broadband Compact Light Sources

Abstract

In modern technology devices, an energy‐saving miniature near‐infrared (NIR) light source plays a critical role in non‐destructive, non‐invasive sensing applications and further advancement of technology. This paper reports the broadband NIR luminescence of Cr3+ clusters for designing phosphor‐converted NIR light‐emitting diodes as an alternative to typical isolated Cr3+ centers and Cr3+ ion pairs. Here, Cr3+ clusters form in the intermediate spinel structure of MgGa2O4 by utilizing the long‐chain edge‐shared octahedral dimers with the shortest bond distance between Cr3+ cations. Electron paramagnetic and magnetometry measurements confirm the isolated Cr3+ and Cr3+ clusters, resulting in NIR luminescence with three distinct emission centers. The formation of Cr3+ clusters in MgGa2O4 ensures stable internal quantum efficiency (≈94%), full‐width‐half‐maximum (248 nm), thermal stability (87%), and a radiant flux of ≈17.66 mW. This work offers a promising approach to NIR phosphor design and enhances the understanding of luminescence mechanisms in spinel and related structures.

Ultrahigh Quantum Efficiency Near-Infrared-II Emission Achieved by Cr3+ Clusters to Ni2+ Energy Transfer

“…Basic luminescence properties of single-doped Cr 3+ and Ni 2+ in the MgGa 2 O 4 structure were reported previously by Rajendran et al and Suzuki et al, and therefore, we focus on the codoped system. The photoluminescence (PL) spectrum of single-doped Cr 3+ samples is shown in Figure a as a function of the Cr 3+ doping.…”

“…Figure f shows the EPR spectrum for a selected Mg 1– y Ga 2– x O 4 : x Cr 3+ , y Ni 2+ compound at T ≈ 80 K in the range of up to 700 mT. In the EPR signal, it is possible to distinguish EPR lines originating from single Cr 3+ , single Ni 2+ , Cr 3+ clusters, and Cr 3+ –Ni 2+ ion pairs, with the effective spectroscopic splitting ratio g eff = 4.74/2.54, 2.22, 1.98, and 1.83, respectively. − The presence of Cr 3+ clusters has been found and investigated by Rajendran et al The samples are reproduced and measured in Figure S5a and fitted using the Curie–Weiss model for single Cr 3+ and the Bleaney–Bowers (BB) model for Cr 3+ clusters. , The Ni 2+ -doped-only samples are also synthesized and measured at 80 K in Figure S5b. The results indicate that the signal originates from a single Ni 2+ in the octahedral site rather than NiO, where Ni 2+ ions strongly interact with each other and where the intensity of the signal increases with increased Ni 2+ concentration .…”

“…The photoluminescence (PL) spectrum of single-doped Cr 3+ samples is shown in Figure a as a function of the Cr 3+ doping. The emission spectrum consists of three bands, the R-band (708 nm), the N-band (750 nm), and the C-band (850 nm), arising from the emission of single Cr 3+ , Cr 3+ –Cr 3+ pairs, and Cr 3+ clusters, respectively . The IQE of the samples is listed in Table S5, where an IQE > 97% up to x = 0.06 is found.…”

“…Miao et al reported the intermediate spinel-type structured phosphor MgGa 2 O 4 :Cr 3+ ,Ni 2+ with an ultrahigh IQE of 96.5%; however, the structural properties and luminescent mechanism were not investigated. Focusing on the MgGa 2 O 4 system, Yao et al reported the likely existence of Cr 3+ –Cr 3+ ion pairs in the MgGa 2 O 4 intermediate spinel-type structure, and Rajendran et al reported the presence of Cr 3+ clusters in an intermediate spinel-type structured material. Therefore, our work leverages insights into the high-efficiency energy transfer from Cr 3+ clusters to Ni 2+ in the intermediate spinel MgGa 2 O 4 structure to achieve ultrahigh IQE in the NIR-II region.…”