Influence of Ce³⁺ Concentration on the Thermal Stability and Charge-Trapping Dynamics in the Green Emitting Phosphor CaSc₂O₄:Ce³⁺

Abstract

The influence of the Ce3+ concentration on the excitation and emission characteristics, thermal stability, and charge-trapping–detrapping dynamics, of the green-emitting phosphor Ce3+ doped calcium scandium oxide (CaSc2O4) with very dilute Ce3+ substitutions (0.5, 1.0, and 1.5%), has been investigated using optical spectroscopy techniques. The diffuse reflectance and excitation spectra are found to exhibit a nonsystematic behavior with varying Ce3+ concentration, mainly linked to spectral band-overlap, whereas the emission spectra display only minor changes with varying Ce3+ concentration, suggesting that the local structural coordination of the Ce3+ dopants remains the same for different Ce3+ dopant levels. The major impact of Ce3+ concentration is seen on the thermal quenching temperature, which is found to be as high as T 50% ≈ 600 K for the most dilute Ce3+ doping (0.5%), followed by T 50% ≈ 530 K for 1.0% doping and T 50% ≈ 500 K for 1.5% doping, respectively. The materials are found to display a red-shift of the emitted light from 518 to 535 nm with increasing temperature from T = 80 K to T = 800 K, for all Ce3+ dopant levels. Thermoluminescence glow curves provide evidence for five charge-trapping defects, which are found to exhibit different charge-trapping dynamics for excitation into different 5d levels. It is argued that the three deeper traps can be filled by athermal tunneling of charges from the Ce3+ 5d 1 level, while the two shallower traps can only be filled when the charges move through the conduction band of the material.

Effects of the deep traps on the thermal‐stability property of CaAl2O4: Eu2+ phosphor

“…White light emitting diodes (wLEDs) have been widely used in daily life due to their eco‐friendly properties, easy fabrication, high efficiency, low cost, and long luminescent lifetime . The traditional wLEDs are prepared by combining a blue LED chip with yellow‐emitting Y 3 Al 5 O 12 : Ce 3+ (YAG: Ce 3+ ) phosphors . Another approach for producing wLEDs is via combining red‐, green‐, and blue‐emitting phosphors with a near ultraviolet (NUV) LED chip .…”

The crucial impact of cerium reduction on photoluminescence

“…In addition to an absorption band below 400 nm, the reduced samples present a new absorption band, compared to CSO-0, centered at 445 nm. This band, corresponding to the material maximum of excitation, [15,19] presents a continuous increase with the reduction duration and a stabilization of its intensity between CSO-48 and CSO-96. This band is correlated to the presence of Ce 3+ [19] and confirms the increase of the Ce 3+ ratio with reduction.…”

“…This band, corresponding to the material maximum of excitation, [15,19] presents a continuous increase with the reduction duration and a stabilization of its intensity between CSO-48 and CSO-96. This band is correlated to the presence of Ce 3+ [19] and confirms the increase of the Ce 3+ ratio with reduction. Moreover, the absence of band at 445 nm for the non-reduced sample (CSO-0) suggests that Ce 3+ cations are not present in this sample (at least at the detection threshold of the technique), implying a sample mainly doped with Ce 4+ .…”

“…Diffuse reflection has been proved to be an appropriate tool to probe the presence of Ce 3+ in CaSc 2 O 4 . [19] In this context, the spectra of samples CSO-0 to CSO-96 were collected (Fig. 1(b)).…”

Partial cation substitution of tunable blue‐cyan‐emitting Ba2B2O5:Ce3+ for near‐UV white LEDs

“…Ce 3+ ion with 4f-5d allow transition usually exhibits blue light with strong emission intensity and broad emission band in many hosts. 14,15 The emission and excitation bands of Ce 3+ ion can be tuned by changing the coordination environment, so that the luminescence properties can be controlled. There are two methods to change the coordination environment.…”