Mn5+-activated Ca6Ba(PO4)4O near-infrared phosphor and its application in luminescence thermometry

Abstract

The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited into the broad and strong absorption band that spans the 500–1000 nm spectral range, this phosphor provides an ultranarrow (FWHM = 5 nm) emission centered at 1140 nm that originates from a spin-forbidden 1E → 3A2 transition with a 37.5% internal quantum efficiency and an excited-state lifetime of about 350 μs. We derived the crystal field and Racah parameters and calculated the appropriate Tanabe–Sugano diagram for this phosphor. We found that 1E emission quenches due to the thermally-assisted cross-over with the 3T2 state and that the relatively high Debye temperature of 783 K of Ca6Ba(PO4)4O facilitates efficient emission. Since Ca6Ba(PO4)4O also provides efficient yellow emission of the Eu2+ dopant, we calculated and explained its electronic band structure, the partial and total density of states, effective Mulliken charges of all ions, elastic constants, Debye temperature, and vibrational spectra. Finally, we demonstrated the application of phosphor in a luminescence intensity ratio thermometry and obtained a relative sensitivity of 1.92%K−1 and a temperature resolution of 0.2 K in the range of physiological temperatures.

Mn5+ Lifetime‐Based Thermal Imaging in the Optical Transparency Windows Through Skin‐Mimicking Tissue Phantom

“…[ 33,34 ] Moreover, its narrow (full width at half maximum, FWHM < 5 nm) and intense emission associated with the 1 E→ 3 A 2 transition from the host materials studied so far is located in the 1100 – 1200 nm range, which ideally falls within NIR‐II [ 32 ] . [ 33 ] The main limitation of Mn 5+ is the need to select a host material that allows the stabilization of the manganese ions at the 5+ oxidation state. According to Shannon, [ 35 ] Mn 5+ exists only in a tetrahedral configuration, and its effective ionic radius is relatively small (33 pm).…”

“…[29] Among TM ions, as recently shown by Ristic et al, Mn 5+ ions meet all the criteria for a robust temperature probe. [32,33] Despite the expected influence of the crystal field on its spectroscopic properties, some of its absorption bands are located within NIR-I, which allows Mn 5+ ions to be efficiently excited through tissues. [33,34] Moreover, its narrow (full width at half maximum, FWHM < 5 nm) and intense emission associated with the 1 E→ 3 A 2 transition from the host materials studied so far is located in the 1100 -1200 nm range, which ideally falls within NIR-II [32] .…”

“…[32,33] Despite the expected influence of the crystal field on its spectroscopic properties, some of its absorption bands are located within NIR-I, which allows Mn 5+ ions to be efficiently excited through tissues. [33,34] Moreover, its narrow (full width at half maximum, FWHM < 5 nm) and intense emission associated with the 1 E→ 3 A 2 transition from the host materials studied so far is located in the 1100 -1200 nm range, which ideally falls within NIR-II [32] . [33] The main limitation of Mn 5+ is the need to select a host material that allows the stabilization of the manganese ions at the 5+ oxidation state.…”

Shell Engineering on Thermal Sensitivity of Lifetime-Based NIR Nanothermometers for Accurate Temperature Measurement in Murine Internal Liver Organ

“…With noncontact infrared thermography, it is hard to measure the temperature inside the object, which is inherently limited by any medium or obstacle between the detector and the target, so it cannot be combined with the optical microscopy. The developed luminescent thermometry based on nanoprobes can address these concerns and detect temperature at nanoscale in a noninvasive way, which is becoming increasingly eye-catching. − …”

Excited-State Dopant–Host Energy-Level Alignment: Toward a Better Understanding of the Photoluminescence Behaviors of Doped Phosphors

“…The host lattice can also be excited and transfer its excitation energy to the activator, acting as a sensitizer. − The nature of both the activator ion and the host lattice determines the absorption and emission behaviors. The most commonly used activator ions, present in relatively low concentrations, are intentionally doped rare-earth ions, − transition metal ions, − d 10 ions, − and s 2 ions. − The common lattice matrices generally are insulators, meaning they have large bandgaps. Thus, a dopant–host phosphor generally exhibit type I energy-level alignment, which favors energy transfer from the host to the activator. − In contrast, if the energy level is type II, exciton dissociation and thus photoluminescence (PL) quenching may occur, which is not desiable when designing luminescent materials.…”