Fiber optic thermometer using Cr-doped GdAlO₃broadband emission decay

Abstract

Luminescence decay temperature measurements are performed from 800 to 1200 °C using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor tip on a YAG single crystal fiber. As a thermographic phosphor, Cr:GdAlO3 combines the intense luminescence of transition metal dopants with the high temperature long decay times usually exhibited only by rare earth dopants. The proposed mechanism is emission by the Cr3+ dopant via the spin-allowed 4T2 → 4A2 transition supported by a reservoir state in 2E which populates (2E → ) through thermal equilibration. The relative energy levels and transition probabilities associated with the strong crystal field at the Al3+ site in the perovskite structure of GdAlO3 are favorable for suppressing thermal quenching of luminescence. Results from a single-fiber configuration sensor, based on a YAG fiber for its low background luminescence, are presented. Using a decay curve fitting procedure that accounts for background fluorescence, accuracies of better than ±5 °C are demonstrated.

Multimodal Non-Contact Luminescence Thermometry with Cr-Doped Oxides

“…To compare the relative sensitivity of different crystals and in different regimes of temperature measurements, we use a value of = 1 K as a separator between high and low resolution of a temperature sensor. The temperature resolution typically reported for non-contact luminescence sensors using decay time and intensity ratio techniques can vary over a broad range from 5 × 10 −3 to 5 K [ 2 , 6 , 8 , 9 , 23 , 27 , 38 , 56 , 74 , 87 , 88 , 89 , 90 ].…”

“…Research into ruby-based luminescence lifetime thermometry resulted in good precision and reliability [ 47 ] and, thus, the method is used for temperature monitoring over a relatively wide range [ 48 , 49 , 50 , 51 , 52 ]. The feasibility of other Cr-doped luminescence sensors for luminescence thermometry has been shown in many other materials, including garnets Y 3 Al 5 O 12 [ 53 ], Gd 3 Al 5 O 12 [ 54 ], perovskites YAlO 3 [ 55 ], GdAlO 3 [ 56 ], alexandrite BeAl 2 O 4 , [ 57 ], spinel MgAl 2 O 4 [ 58 ], borates YAl 3 (BO 3 ) 4 [ 59 ], gallates Bi 2 Ga 4 O 9 [ 60 ], aluminates LiAl 5 O 8 [ 61 ], etc.…”

Surface temperature measurements from a stator vane doublet in a turbine afterburner flame using a YAG:Tm thermographic phosphor

“…Uniform decay rates were expected because the largest energy difference between adjacent 1 D 2 sublevels of 146 cm −1 is sufficiently small for thermal equilibrium to be maintained between Stark sublevel populations at room temperature. For temperature calibration purposes, a decay time was determined for each decay curve based on a previously developed conditional exponential fitting procedure [24] in which a consistent, unbiased fitting range was based on intensity threshold criteria [25]. In this procedure, the combination of a fast initial decay followed by a uniform slower decay was addressed by fitting a double exponential to the decay curves:…”

“…The intensity threshold approach used previously [24] was adapted where the intensity threshold crossings at 60% and 10% of the initial intensity were selected as the start and end of the fitting range, respectively. Early decay artifacts and lower signal to noise in the afterburner probe measurements, as observed in figure 16, restricted the fitting range further than what would be necessary for the furnace calibration 12.…”

Single fiber temperature probe configuration using anti-Stokes luminescence from Cr:GdAlO3

“…Luminescence decay-based fiber optic thermometers have attracted considerable interest for their ability to probe temper atures in harsh environments where their immunity to chemical attack and electromagnetic interference as well as minimal intrusiveness are significant advantages over either thermocouples or electrical-resistance based thermometers [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. While single fiber probe configurations for luminescence-based fiber optic thermometers as well as for fluorescence and Raman probes have been recognized to offer advantages of simple design, compactness, perfect excitation/ collection zone alignment, and high light collection efficiency, their effective use has been greatly limited by background interference by emission or scattering generated in the fiber probe itself as well as the excitation and collection fibers coupled to the probe [15][16][17][18][19][20].…”