Thermometry based on trivalent dysprosium luminescence: theoretical modeling of thermometrical performances

[A. Martinović]

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Fizika - Primenjena fizika / Physics - Applied physics

Luminescentna termometrija koristi temperaturno zavisnu emisiju svetlosti za merenje temperature na daljinu. Dy3+ jon je utvrđen kao perspektivan jon za visokotemperaturne sonde, ali s obzirom na to da postoji beskonačan broj potencijalnih matrica nemoguće je konvencionalnim putem naći onu sa najboljim performansama. Razlog tome je što tradicionalna termometrija podrazumeva merenje spektara na više temperatura i kompleksnu obradu podataka, što iziskuje mnogo vremena, energije i sredstava. Džad-Ofeltov termometrijski model može predvideti osetljivosti, ali do sada nije bio eksperimentalno potvrđen za Dy3+ jon. Po prvi put smo se bavili određivanjem najbolje matrice za Dy jon za termometriju pomoću LIR metode i predviđanjem termometrijskih veličina pomoću Džad-Ofeltove teorije. Dodatno, u analizu smo uključili i 3. termalizovani nivo Dy čija primena na visokim temperaturama dovodi do značajnog povećanja osetljivosti. Pozicije energijskih nivoa, vrednosti indeksa prelamanja, Džad-Ofeltovi parametri intenziteta, Slaterovi integrali, kao i parametri spin-orbitalne sprege, su uzeti iz literature za 27 Dy3+ dopiranih materijala (5 kristala i 22 stakla). Istraživani su samo prelazi koji se koriste za termometre koji se zasnivaju na odnosu intenziteta luminescencije (LIR) Bolcmanovog tipa (prelazi sa tri termalizovana nivoa 4F9/2, 4I15/2 i 4G11/2 na osnovni nivo). Redukovani matrični elementi ova tri prelaza su izračunati pomoću Slaterovih integrala i parametara spin-orbitalne sprege i upoređeni su sa najčešće korišćenim vrednostima iz Karnalovih tabela. Poređenje Džad-Ofeltovih parametara pokazalo je manju varijaciju Ω6 parametra, vezanog za rigidnost, u kristalnim matricama nego u staklima, a suprotno je primećeno za Ω2,4 parametre. Performanse LIR-a su simulirane Džad-Ofeltovim termometrijskim modelom za svaki materijal konvencionalnim LIR-om i LIR-om koji koristi treći termalizovani nivo. Poređenjem predviđenih veličina u luminescentnoj termometriji otkriveni su Dy3+ dopirani kristali i stakla čija termometrijska primena najviše obećava. Radi testiranja poklapanja rezultata predviđenih Džad-Ofeltovim termometrijskim modelom i eksperimentalno dobijenih rezultata konvencionalne termometrije, korišćena je dobro poznata Dy dopirana matrica CaYAlO4:Dy3+. Čista faza CaYAlO4:Dy3+ praha je sintetizovana putem modifikovane Pechini metode. Fotoluminescentni spektri su snimani od 300 do 600 K. Odnos intenziteta luminescencije je procenjen koristeći 4I15/2 i 4F9/2 nivoe. Eksperimentalno dobijene vrednosti termometrijskih parametara i osetljivosti su pokazale odlično slaganje sa onim dobijenim Džad-Ofeltovim modelom, ukazujući na potencijalnu primenu Džad-Ofeltovog modela za brzu procenu termometrijske perspektive Dy3+ dopiranih luminescentnih senzora. Maksimalne apsolutne i relativne osetljivosti su ~0.001 K-1 na 600 K i ~1.4% K-1 na 300 K, redom. Optimalni temperaturni opseg za CaYAlO4:Dy3+ sondu je od 370 do 616 K.

Luminescence thermometry uses temperature-dependent emission of light for remote sensing. Dy3+ is established as a perspective ion for high temperature probes, but given that there is an infinite number of potential hosts it is impossible to find conventionally the one with the best performance. The reason behind this is that traditional thermometry involves measuring spectra at multiple temperatures and complex data processing, which requires a lot of time, energy, and resources. Judd-Ofelt thermometric model can predict sensitivities, but it has not been experimentally validated on Dy3+ ion so far. For the first time, we dealt with the determination of the best Dy ion matrix for thermometry using the LIR method and the prediction of thermometric quantities using the Judd-Ofelt theory. In addition, we included in the analysis the 3rd thermalized level of Dy, the application of which at high temperatures leads to a significant increase in sensitivity. Energy level positions, refractive index values, Judd-Ofelt intensity parameters, Slater integrals, and spin-orbit coupling parameters were taken from the literature for 27 Dy3+ doped materials (5 crystals and 22 glasses). Investigated were only the transitions that are used for the Boltzmann-type luminescence intensity ratio (LIR) thermometers (transitions from the three thermalized levels 4F9/2, 4I15/2 and 4G11/2 to the ground level). Reduced matrix elements of these three transitions were calculated from the Slater integrals and spin-orbit coupling parameters and they are compared to the most frequently used values from Carnall’s tables. The comparison of Judd-Ofelt parameters showed the smaller variation of the Ω6, related to rigidity, in crystal hosts than in glasses, and the opposite was observed for the Ω2,4 parameters. LIR performances were simulated by the Judd-Ofelt thermometric model for each material by the conventional LIR and the LIR that exploits the third thermalized level. The comparison of the predicted figures of merit in luminescence thermometry revealed the most promising thermometric Dy3+ doped crystals and glasses. To test the agreement between the results predicted by the Judd-Ofelt thermometric model and the experimentally obtained results of conventional thermometry, the well-known Dy doped matrix CaYAlO4:Dy3+ was used. Pure phase CaYAlO4:Dy3+ powder was synthesized via the modified Pechini method. Photoluminescence spectra were taken from 300-600 K. Luminescence intensity ratio was estimated using 4I15/2 and 4F9/2 levels. Experimentally obtained thermometric parameters and sensitivities showed an excellent matching with those obtained from the Judd-Ofelt, indicating the potential application of the Judd-Ofelt model for fast assessment of Dy3+-doped luminescent sensor thermometric perspective. The maximum absolute and relative sensitivities are ~0.001 K-1 at 600 K and ~1.4% K-1 at 300 K, respectively. The optimum temperature range for the CaYAlO4:Dy3+ probe is from 370-616 K.

Džad-Ofelt, fotoluminescencija, termometrija, disprozijum

Judd-Ofelt, photoluminescence, thermometry, dysprosium

536.51:535.37(043.3)

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