Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr₃Y(PO₄)₃:Yb³⁺/Ln³⁺ phosphors (Ln=Ho, Er, Tm)

Abstract

Phase-pure eulytite-type Sr3Y0.88(PO4)3:0.10Yb3+,0.02Ln3+ upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er3+), 657 nm red (Ho3+) and 476 nm blue (Tm3+) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 μs, respectively. It was shown that (1) the Er3+ doped phosphor has a better overall performance of temperature sensing with thermally coupled 2H11/2 and 4S3/2 energy levels, whose maximum absolute (SA) and relative (SR) sensitivities are ~5.07 × 10−3 K−1 at 523 K and ~1.16% at 298 K, respectively; (2) the Ho3+ doped phosphor shows maximum SA and SR values of ~0.019 K−1 (298–573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of 5F5/(5F4,5S2) and 5I4/5F5, respectively; (3) the Tm3+ doped phosphor has a maximum SA of ~12.74 × 10−3 K−1 at 573 K for the non-thermally coupled 3F2,3/1G4 energy levels and a maximum SR of ~1.74% K−1 at 298 K for the thermally coupled 3F2,3/3H4 levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors.

Phase evolution, structure, and up‐/down‐conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho, Er, Tm)

“…It is also seen from Figure A that the green band well splits into four sharp peaks centered at ~ 524, 540, 551 and 568 nm, respectively, which indicates that the 2 H 11/2 and 4 S 3/2 energy levels of Er 3+ are subjected to substantial splitting by the dodecahedral coordination environment in Li 6 CaLa 2 Nb 2 O 12 . Such a phenomenon was found for Gd 2 O 3 :Yb/Er, Y 2 O 3 :Yb/Er, LiYF 4 :Yb/Er, and NaLu(WO 4 ) 2 :Yb/Er, but hardly for YbPO 4 :Er, YPO 4 :Yb/Er and Sr 3 Y(PO 4 ) 3 :Yb/Er orthophosphates, La 2 O 2 S:Yb/Er oxysulfide, and La 2 O 2 SO 4 :Yb/Er oxysulfate . In addition, the broad and diffuse red luminescence extending from ~ 640 to 700 nm (Figure A) was similarly observed for Ba 5 Gd 8 Zn 4 O 21 :Yb/Er UC phosphor in the ~ 640‐680 nm spectral region, which was ascribed to widening of the 4 F 9/2 energy level by electronic interactions and spin‐orbit coupling .…”

NIR light guided enhanced photoluminescence and temperature sensing in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor

“… Rare earths and materials Transition Temperature (K) Sensitivity (S) (K −1 ) × 10 −4 at temp. (K) References Ho 3+ –Yb 3+ : Gd 2 O 3 5 F 4 / 5 S 2 → 5 I 8 300–800 18.0 (580) (S R ) 13.0 (798) (S A ) 17 Ho 3+ –Yb 3+ : BaTiO 3 5 F 4 / 5 S 2 → 5 I 8 12–300 2.0 (300) (S R ) 45 Ho 3+ /Yb 3+ (Glass–ceramic) 5 F 2,3 / 3 K 8 , 5 F 1 / 5 G 6 → 5 I 8 303–643 and 1119 10.2 (1119) (S R ) 47 Ho 3+ /Yb 3+ : Sr 3 Y(PO 4 ) 3 5 I 4 / 5 F 5 → 5 I 8 298–573 4.6 (573) (S A ) 48 Tm 3+ /Yb 3+ : Sr 3 Y(PO 4 ) 3 3 F 2,3 / 1 G 4 → 3 H 6 298–573 15.3 (573) (S A ) 48 Nd 3+ (Glass–ceramic) 4 F 5/2 / ...…”

Na(Gd,RE)(WO4)2 double tungstates (RE=Eu/Yb-Er): crystallization from a novel layered hydroxide precursor and favorable luminescence for optical thermometry

“…At the highest measurement temperature of 548 K (275°C), the intensity of 524, 520, 530 nm drops to 67.7%, 87.9%, and 58.6% of the initial value, respectively. While the 4 right after the temperature increased and the intensity loss of the emission is mostly due to enhanced nonradiative relaxation by intensified lattice vibration at a higher temperature [8,39]. At the highest measurement temperature of 548 K (275°C), the intensity of 543, 552, 656, and 670 nm drops to 17.1%, 14.4%, 28.8%, and 26.3% of the initial value, respectively.…”

“…This further indicated that the phosphor can be used for luminescence thermometry. The quality of optical thermometry can be quantified via absolute sensitivity (S A ) and relative sensitivity (S R ) and Figure 10b shows the results of S A /S R derived from the following equations [8,9]:…”

“…Ln 3+ -based phosphors are versatile, stable, and in general with high emission quantum yields. Various systems have been investigated as optical thermometers such as SrY 2 O 4 : Bi 3+ ,Eu 3+ [6], Gd 4 O 3 F 6 : Ho 3+ ,Yb 3+ [7], Sr 3 Y(PO 4 ) 3 :Yb 3 + /Ln 3+ [8], Sr 3 Ce(PO 4 ) 3 :Tb 3+ /Mn 2+ [9], Li 6 CaLa 2 Nb 2 O 12 : Yb/Er [10], Ce 3+ -Eu 2+ in LiSr 4 (BO 3 ) 3 [11], Er:Yb:NaY 2 F 5 O [12], etc. It was found that phosphors have good thermal stability tend to show favorable sensing properties.…”