Producing Tunable Broadband Near-Infrared Emission through Co-Substitution in (Ga_1–<i>x</i>Mg_<i>x</i>)(Ga_1–<i>x</i>Ge_<i>x</i>)O₃:Cr³⁺

Broadband near-infrared (NIR) phosphors are in high demand for creating “smart” NIR phosphor-converted light-emitting diode (pc-LED) sources. In this work, a series of Cr3+-substituted NIR-emitting materials with highly efficient, broad, tunable emission spectra are achieved by modifying the simple oxide Ga2O3 using [Mg2+-Ge4+] and [Ga3+-Ga3+] co-unit substitution. The results show that the emission peak can be shifted from 726 to 830 nm while maintaining a constant excitation peak in the blue light region, enabling extensive application. The optical properties stem from changes in the Cr3+ crystal field environment upon substitution. Intriguingly, the temperature-dependent photoluminescence emission peak position shows virtually no change in the [Mg2+-Ge4+] co-substituted materials. This abnormal phenomenon is found to be a comprehensive embodiment of a weakening crystal field environment (red-shift) as the temperature increases and reduced local structure distortion (blue-shift) with increasing temperature. The high quantum yield, NIR emission, and net-zero emission shift as a function of temperature make this phosphor class optimal for device incorporation. As a result, their performance was studied by coating the phosphor on a 450 nm emitting LED chip. The fabricated device demonstrates an excellent NIR output power and NIR photoelectric conversion efficiency. This study provides a series of efficient, tunable, broadband NIR materials for spectroscopy applications and contributes to the basic foundation of Cr3+-activated NIR phosphors

Origin of Spectral Blue Shift of Lu³⁺-Codoped YAG:Ce³⁺ Phosphor: First-Principles Study

Lu³⁺, with the smallest ionic radii in lanthanide ions, is an important and beneficial cation for tuning spectrum shifting toward a longer wavelength by ion substitution in many phosphors for solid-state lighting. However, in the Lu³⁺-substituted garnet system, the phosphor always has smaller lattice parameters and exhibits a shorter emission wavelength than other garnet phosphors. The mechanism of such a spectral blue shift induced by the Lu³⁺-codoped garnet phosphor is still unclear. In this study, the local and electronic structures of Lu³⁺-codoped and Lu³⁺-undoped YAG:Ce³⁺ phosphor have been studied by first-principles calculation to reveal the origin of the spectral blue shift. Our results provide a full explanation of the experimental data and the methodology, which is useful to understand and design garnet phosphors with tunable emission characteristics

Identifying the Emission Centers and Probing the Mechanism for Highly Efficient and Thermally Stable Luminescence in the La₃Si₆N₁₁:Ce³⁺ Phosphor

Nitride La₃Si₆N₁₁:Ce³⁺ is an important commercial phosphor for high-power white light-emitting diodes due to its strong resistance toward thermal quenching and sufficient emission efficiency. However, the underlying mechanisms of this high performance is still a mystery. Also, the emission properties of Ce³⁺ in two kinds of crystallographic sites are currently in dispute. Here, we confirmed the yellow emission ascribed to Ce_La(2) luminescence center and proposed a blue emission owning to Ce_La(1) luminescence center through both theoretical and experimental methods. Particularly, we find an unusual efficient and fast energy transfer from Ce_La(1) to Ce_La(2) due to a large spectral overlap between the emission of Ce_La(1) and the absorption of Ce_La(2), and efficient electron transfer from defects to 5d orbital at high temperature, which shows high relevance to the highly efficient yellow emission and thermal stability of this material. This study presents a full and new understanding toward this special phosphor and provides useful insights into designing highly efficient and thermally stable luminescent materials for future lighting

Highly Efficient and Stable Narrow-Band Red Phosphor Cs₂SiF₆:Mn⁴⁺ for High-Power Warm White LED Applications

Due to the unique narrow-band red emission and broadband blue light excitation, as well as milder synthesis conditions, Mn⁴⁺ ion activated fluoride red phosphors show great promise for white light emitting diode (W-LED) applications. However, as the Mn⁴⁺ emission belongs to a spin-forbidden transition (²E_g → ⁴A₂), it is a fundamental challenge to synthesize these phosphors with a high external quantum efficiency (EQE) above 60%. Herein, a highly efficient and thermally stable red fluoride phosphor, Cs₂SiF₆:Mn⁴⁺, with a high internal quantum efficiency (IQE) of 89% and ultrahigh EQE of 71% is demonstrated. Furthermore, nearly 95% of the room-temperature IQE and EQE are maintained at 150 °C. The static and dynamic spectral measurements, as well as density functional theory (DFT) calculations, show that the excellent performance of Cs₂SiF₆:Mn⁴⁺ is due to the Mn⁴⁺ ions being evenly distributed in the host lattice Cs₂SiF₆. By employing Cs₂SiF₆:Mn⁴⁺ as a red light component, stable 10 W high-power warm W-LEDs with a luminous efficiency of ∼110 lm/W could be obtained. These findings indicate that red phosphor Cs₂SiF₆:Mn⁴⁺ may be a highly suitable candidate for fabricating high-performance high-power warm white LEDs