Comment on a zero-thermal-quenching phosphor

TL;DR

This paper critically examines a claimed zero-thermal-quenching phosphor, revealing that its supposed non-quenching behavior is likely due to experimental artifacts rather than intrinsic material properties.

Contribution

The study challenges previous claims of zero thermal quenching in a specific phosphor by providing a detailed optical analysis and identifying potential measurement pitfalls.

Findings

Observed increase in emission intensity with temperature is likely an experimental artifact.

Optical characterization points to thermal expansion and phase transitions affecting measurements.

Claims of zero thermal quenching are not supported by comprehensive optical data.

Abstract

Kim and co-authors in a recent article reported a phosphor Na3-2xSc2(PO4)3:xEu2+ (NSPO:xEu2+) that did not exhibit thermal quenching (TQ) even up to 200 degree Celsius. The authors suggested that zero-TQ originates from the compensation of emission losses due to the polymorphic nature of the host and the energy transfer from traps consisting of electron-hole pairs to the 5d-band of Eu2+, leading to radiative recombination. The temperature-dependent excitation and emission spectra seemingly supported the authors' assertion. However, a close inspection of the CIE chromaticity coordinates and correlated color temperature (CCT) the WLED prototype fabricated using NSPO:0.03Eu2+ , La3Si6N11:Ce3+ and (SrCa)AlSiN3:Eu2+ as a blue, yellow and red-emitting component respectively (abbreviated as WLED device hereafter) under operating currents of 100-1000 mA alongside a series of optical characterization results of NSPO:xEu2+ indicates that the so-called zero-TQ should not be the case. There were some questionable points in optical characterization of the phosphors. The observed increase in intensity upon elevating temperature in the temperature-dependent excitation and emission spectra was likely a pitfall caused by optical path length variation of the spectrofluorimeter induced by lattice thermal expansion and phase transitions.