Site occupancy and enhanced luminescence of broadband NIR gallogermanate phosphors by energy transfer

Abstract

Super broadband near‐infrared (NIR) La3Ga5GeO14(LGGO): Cr3+ phosphor is in urgent needs for food testing. Unfortunately, it suffers from poor luminescence intensity in applications. Herein, the enhanced NIR luminescence performance can be realized in LGGO: Pr3+, Cr3+. The preferential crystallographic site of Cr3+ is validated on the basis of EPR spectrum, Rietveld refinement, and the first‐principles DFT calculations. It is of great importance that the as‐prepared phosphors can be excited by blue light (460 nm), which is beneficial to the application of blue‐pumped LEDs. The critical distance of Pr3+ in LGGO host has been calculated by concentration‐quenching method. For co‐doped sample, it is observed that Cr3+ luminescence intensity enhancement by a factor of 3 can be achieved by doping Pr3+ owing to the energy transfer from Pr3+ to Cr3+. In addition, the introduction of Pr3+ can also improve the Cr3+ luminescence intensity at elevated temperature. Furthermore, using the optimized phosphor, a blue‐based NIR phosphor‐converted LEDs (NIR pc‐ LEDs) is fabricated, the forward voltage and the intensity of LED hardly change after thermal aging for 500 hours under high temperature/ high humidity condition, indicating its great reliability for NIR pc‐LEDs. Therefore, LGGO:Pr3+, Cr3+ has great potential to serve as an attractive candidate in the application of blue light‐excited NIR pc‐LEDs in view of its capability for blue to enhanced broadband NIR conversion.

A High Efficiency Trivalent Chromium-Doped Near-Infrared-Emitting Phosphor and Its NIR Spectroscopy Application

“…With further discussion, such a peak indicates the occupation of the Cr 3+ ions on the crystal lattice within Sc 3+ ions. The peak at approximately g = 2.00 corresponds to the tetrahedral condition of chromium ions . This implies an oxidation process of transferring a small amount of Cr 3+ in the sample into Cr 4+ with the occupation in the lattice position of Si 4+ within the crystal.…”

Crystal‐Field Engineering Control of an Ultraviolet–Visible‐Responsive Near‐Infrared‐Emitting Phosphor and Its Applications in Plant Growth, Night Vision, and NIR Spectroscopy Detection

“…The resonance signal near g = 4.9 was generated by the Cr 3+ ion at the center of the six‐coordinate octahedron (Al1, Al4), whereas the resonance signal near g = 1.86 was produced by the exchange‐coupled Cr 3+ –Cr 3+ ion pairs at the four‐coordinate tetrahedral site (Al2, Al3). [ 21 ] These results show that Cr 3+ occupied the six‐coordinate octahedral sites and four‐coordinate tetrahedral sites in this system. According to previous reports, Cr 3+ is more likely to occupy the six‐coordinate octahedral site of Al 3+ : additionally, the peak at 700 nm (I 1 ) is a luminescence peak that represents Cr 3+ in a six‐coordinate octahedral crystal field environment, and is typically indicative of a strong crystal field.…”

Thermally Stable Phosphor KBa2(PO3)5:Eu2+ with Broad-Band Cyan Emission Caused by Multisite Occupancy of Eu2+

“…It is well-known that exchange interaction is the dominant role only if R c is shorter than 5 Å, and thus the concentration quenching in KBP: x Eu is more likely through the electric–multipolar interaction. Moreover, the multipolar interaction type can be determined by the following equation: − where I is the emission intensity at the current concentration, x means the Eu 2+ concentration, and the values of k and β are constant. The constant θ determines the type of electric–multipolar interaction, for which θ = 6, 8, and 10 refers to dipole–dipole (d–d), dipole–quadrupole (d–q), and quadrupole–quadrupole (q–q) interactions, respectively, whereas θ = 3 represents the energy migration between nearest or next-nearest Eu 2+ cations.…”