Chemical Tuning, Pressure, and Temperature Behavior of Mn⁴⁺ Photoluminescence in Ga₂O₃–Al₂O₃ Alloys

Abstract

In this study, we carried out a detailed investigation of the photoluminescence of Mn4+ in Ga2O3–Al2O3 solid solutions as a function of the chemical composition, temperature, and hydrostatic pressure. For this purpose, a series of (Al1–x Ga x )2O3:Mn4+,Mg phosphors (x = 0, ..., 0.1.0) were synthesized and characterized for the first time. A detailed crystal structure analysis of the obtained materials was done by the powder X-ray diffraction technique. The results of the crystal structure and luminescence studies evidence the transformation of the ambient-pressure-synthesized material from the rhombohedral (α-type) to monoclinic (β-type) phase as the Ga content exceeds 15%. Spectroscopic features of the Mn4+ deep-red emission, including the temperature-dependent emission efficiency and decay time, as well as the possibility of their tuning through chemical pressure in each of these two phases were examined. Additionally, it has been shown that the application of hydrostatic pressure of ≥19 GPa allows one to obtain a corundum-like α-Ga2O3:Mn4+ phase. The luminescence properties of this material were compared with β-Ga2O3:Mn4+, which is normally synthesized at ambient pressure. Finally, we evaluated the possibility of application of the studied phosphor materials for low-temperature luminescence thermometry.

Millimeter-Sized K2MnF6:Si4+, NH4+ Red-Luminescent Crystals with High Absorption Efficiency (AEmax of 93.5%) and External Quantum Efficiency (EQEmax of 68.9%) Grown by Cooling-Induced Crystallization

“…In addition, the position of the PL peaks slightly blue-shifts (for example, the ZPL shifts from 623.1 nm for the x = 0.97 sample to 621.7 nm for the x = 0.50 sample) with the decreasing Si 4+ concentration, which could be due to the enhancement of the crystal field around the Mn 4+ ion. 18 Similar to h-K 2 MnF 6 reported by Adachi, 19 the K 2 MnF 6 :Si 4+ , NH 4…”

Evolution of the full energy structure of Mn4+in fluoride phosphors under high pressure conditions

“…Unlike Cr 3+ , Mn 4+ in inorganic hosts was observed only under high crystal field conditions, thus always exhibiting the 2 E -4 A 2 emission. The pressure shift of the 2 E emission of Mn 4+ was observed for Al 2 O 3 , 35 39 and a collection of tungstate 40 and fluoride hosts. 22,23,[41][42][43] Most of these reports, however, lack a detailed discussion of pressure influence on parameters (Dq, B, and C) determining the energy structure of Mn 4+ , except for ref.…”

“…Adachi 44 performed an analysis of Racah parameters of Mn 4+ in KNaSiF 6 :Mn 4+ according to his modified approach, based on the energies of 2 E and 4 T 2 subterms. Zhydachevskyy et al 39 showed an appealing similarity between the effects of the mechanical pressure of Ga 2 O 3 :Mn 4+ and the chemical pressure obtained by creating (Al,Ga) 2 O 3 :Mn 4+ solid solutions. Zheng et al 45 reported Mn 4+ in Gd 2 ZnTiO 6 double perovskite as a bifunctional luminescent pressure and temperature sensor.…”

Polarization and orientation dependent optical properties in Czochralski-grown transition metal doped β-Ga2O3

“…Mn 3+ typically does not luminesce, as heavily Jahn-Teller distorted species tend to have sufficient non-radiative pathways for relaxation [12]. Mn 4+ is also unlikely to be responsible, since Zhydachevskyy et al demonstrated an emission around 710 nm for Mn 4+ doped β-Ga2O3 [18]. This assignment is supported by changes in the intensity of the luminescence following an anneal at 1000 ⁰C for 15 hours in flowing O2.…”

“…It has been thoroughly shown that Cr 3+ in β-Ga2O3 occupies the octahedral site and displays a similar absorption spectrum to ruby, albeit shifted in energy so that a deep green coloration is exhibited [13]. This is due to the weaker crystal field compared to ruby, as is the case with Cr 3+ in emerald [1,18]. While ruby is uniaxial, thus showing two distinct colors in polarized light, β-Ga2O3 is biaxial, displaying three distinct absorptions as shown in Figure 3.…”