A subsurface logging tool deployable in a wellbore that traverses a formation, the logging tool comprising: a tool housing configured for movement within and along the wellbore; and a scintillation detector housed in the tool housing, wherein the scintillation detector includes an activated thallium-based scintillator material, wherein the scintillation detector is a gamma-ray scintillation detector, the tool further comprising:a gamma-ray source configured to emit gamma radiation, wherein the gamma-ray scintillation detector is configured to measure gamma-gamma density of the formation; a voltage source coupled to the gamma-ray scintillation detector; and a stabilization circuit configured to receive output of the gamma-ray scintillation detector, wherein the subsurface logging tool is characterized in that the activated thallium-based scintillator material is represented by the formula Tl 2 MA 1-x Dp x Ha 6; where "Tl" is thallium; where "M" is an alkali metal comprising one of Lithium (Li), Sodium (Na), Potassium, Rubidium (Rb), or Cesium (Cs) or Indium (In) and "x" is a number between 0 and 1; where "A" is a rare earth element comprising one of Yttrium, Lanthanum (La), Praseodymium (Pr), Neodymium (Nd), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), or Lutetium (Lu); where "Dp" is at least one of Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Europium (Eu), Gadolinium (Gd), Terbium (Tb), and Dysprosium (Dy) and "x" is a number between 0 and 1; and where "Ha" is a halide comprising one of chlorine (Cl) (e.g., Fluorine, Bromine (Br), or Iodine; wherein the activated thallium-based scintillator material has a minimum light output of 4,000 ph/MeV when operating at a temperature of 125°C and a minimum light output of 2,500 ph/MeV when operating at a temperature of 200°C; wherein the subsurface logging tool is further characterized in that the gamma-ray source is also configured to measure a reference spectrum emitted by the gamma-ray source and the stabilization circuit is configured to output a feedback signal to the voltage source to control a voltage supplied by the voltage source to the gamma-ray scintillation detector to stabilize a gain of the gamma-ray scintillation detector (240, wherein the feedback signal is based on analysis of characteristics of an escape peak and photo peak in both the reference spectrum and a measured spectrum, from the formation, output by the scintillation detector. a tool housing configured for movement within and along the wellbore; and a scintillation detector housed in the tool housing, wherein the scintillation detector includes an activated thallium-based scintillator material, wherein the scintillation detector is a gamma-ray scintillation detector, the tool further comprising:a gamma-ray source configured to emit gamma radiation, wherein the gamma-ray scintillation detector is configured to measure gamma-gamma density of the formation; a voltage source coupled to the gamma-ray scintillation detector; and a stabilization circuit configured to receive output of the gamma-ray scintillation detector, wherein the subsurface logging tool is characterized in that the activated thallium-based scintillator material is represented by the formula Tl 2 MA 1-x Dp x Ha 6; where "Tl" is thallium; where "M" is an alkali metal comprising one of Lithium (Li), Sodium (Na), Potassium, Rubidium (Rb), or Cesium (Cs) or Indium (In) and "x" is a number between 0 and 1; where "A" is a rare earth element comprising one of Yttrium, Lanthanum (La), Praseodymium (Pr), Neodymium (Nd), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), or Lutetium (Lu); where "Dp" is at least one of Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Europium (Eu), Gadolinium (Gd), Terbium (Tb), and Dysprosium (Dy) and "x" is a number between 0 and 1; and where "Ha" is a halide comprising one of chlorine (Cl) (e.g., Fluorine, Bromine (Br), or Iodine; wherein the activated thallium-based scintillator material has a minimum light output of 4,000 ph/MeV when operating at a temperature of 125°C and a minimum light output of 2,500 ph/MeV when operating at a temperature of 200°C; wherein the subsurface logging tool is further characterized in that the gamma-ray source is also configured to measure a reference spectrum emitted by the gamma-ray source and the stabilization circuit is configured to output a feedback signal to the voltage source to control a voltage supplied by the voltage source to the gamma-ray scintillation detector to stabilize a gain of the gamma-ray scintillation detector (240, wherein the feedback signal is based on analysis of characteristics of an escape peak and photo peak in both the reference spectrum and a measured spectrum, from the formation, output by the scintillation detector.