Photoluminescence Properties of Green-Emitting YBO₃:Ce³⁺,Tb³⁺Phosphor for near UV Excitation

Abstract

YBO3:Ce3+,Tb3+ phosphor was prepared from rare earth oxides and boric acid by a solid state reaction. The phosphor absorbs near UV light through 4f–5d transitions of Ce3+, followed by broad emissions through 5d–4f transitions of Ce3+ and sharp emissions through 4f–4f transitions of Tb3+. Spectroscopic investigations for samples with various Ce3+ and Tb3+ concentrations reveal nonradiative energy transfer from Ce3+ to Tb3+. Emission color of the YBO3:Ce3+,Tb3+ varies from blue (0.163, 0.019) to green (0.321, 0.585) depending on the Ce3+ and Tb3+ concentrations. The optimized green-emitting Y0.82Ce0.03Tb0.15BO3 phosphor has an emission color of (0.309, 0.547) with an external quantum efficiency of 76.7%. The photoluminescence intensity of this phosphor at 150°C keeps 87% of its intensity at room temperature, showing sufficient thermal stability for white light emitting diode applications.

Chemical behavior and spectroscopic properties of rare earth borates in glazes

“…Correspondingly, at 15% Ce 3þ (average distance Ce-Ce¼884 pm), energy migration is yet enhanced and leads to stronger concentration quenching, causing the strongly reduced depreciation in quantum yield to 24%; from the luminescence spectra of purely Ce 3þ -doped phosphor (Y 0.85 Ce 0.05 Tb 0.1 BO 3 , not shown, but compared to Ref. [13]) it is obvious that even at 5% there is a substantial overlap between absorption and emission, which will additionally give rise to selfabsorption, at higher Ce 3 þ content in particular. However, due to the smaller Ce-Tb distance in the 15% sample (here now estimated to be 746 pm), the 417 nm emission of Ce 3 þ is also reduced by more than 50% (see the further discussion in the next paragraph in comparison to corresponding glazes, and Fig.…”

“…The energy transfer boundaries are suboptimal as the excited Ce 3þ would yield electric dipole allowed, broad band d-f emissions, whereas the transitions on the receiving Tb 3þ are dipole forbidden, altogether requiring intimate contacts of only a few hundreds of pm between the couple, i.e. to enable exchange driven energy transfer [12,13,33]. A composition of Y 0.82 Ce 0.03 Tb 0.15 BO 3 , yielding color coordinates of x¼ 0.309, y¼0.547 in the CIE chromaticity diagram, was considered to be optimal with regard to color point and efficiency for application in an UV-LED [13].…”

“…to enable exchange driven energy transfer [12,13,33]. A composition of Y 0.82 Ce 0.03 Tb 0.15 BO 3 , yielding color coordinates of x¼ 0.309, y¼0.547 in the CIE chromaticity diagram, was considered to be optimal with regard to color point and efficiency for application in an UV-LED [13]. For our envisaged use as a powder reference material, higher absorptions, i.e.…”

“…4). In consequence, due to the ease of preparation and reproducibility, the phosphor material can serve as a suitable reference material for Near UV excited green line emitters (see Tables 1 and 2), but has severe bottlenecks in applications for NUV-LEDs, as has been laid out before [13].…”

“…Scanning the available green emitting phosphors for NUV excitation, borates doped with Ce 3 þ and Tb 3 þ drew our attention, as quantum efficiencies for the green emission have been found to range from 40% for pure CeBO 3 :Tb under 345 nm excitation, reported already decades ago [12], to 66% for YBO 3 :Ce, Tb under NUV excitation, as found in a very recent diligent treatise [13]. We should also mention here recent investigations on alkali and alkaline earth borate phases (e.g.…”